A Phase 2/3, Randomized, Observer-Blind, Placebo-Controlled Study to Evaluate the Safety, Reactogenicity, and Effectiveness of mRNA-1273 SARS-CoV-2 Vaccine in Healthy Adolescents 12 to <18 Years of Age
Phase: PHASE2
Conditions: SARS-CoV-2
Sponsor: ModernaTX, Inc.

ModernaTX, Inc. 
mRNA-1273-P203 Protocol Amendment 7 
mRNA-1273 
Confidential 
Page 1 
CLINICAL STUDY PROTOCOL 
Protocol Title: 
A Phase 2/3, Randomized, Observer-Blind, Placebo-Controlled 
Study to Evaluate the Safety, Reactogenicity, and Effectiveness 
of mRNA-1273 SARS-CoV-2 Vaccine in Healthy Adolescents 
12 to <18 Years of Age 
Protocol Number: 
mRNA-1273-P203 
Sponsor Name: 
ModernaTX, Inc.  
Legal Registered 
Address: 
200 Technology Square 
Cambridge, MA 02139 
Sponsor Contact and 
Medical Monitor: 
 
ModernaTX, Inc. 
200 Technology Square 
Cambridge, MA 02139 
Telephone: 
 
e-mail: 
Regulatory Agency 
Identifier Number(s): 
IND: 019745 
Amendment Number: 
7 
Date of Amendment 7: 
19 Oct 2023 
Date of Amendment 6: 
22 Jun 2023 
Date of Amendment 5: 
11 Oct 2022 
Date of Amendment 4: 
25 Jan 2022 
Date of Amendment 3: 
04 Nov 2021 
Date of Amendment 2: 
27 Jul 2021 
Date of Amendment 1: 
23 Mar 2021 
Date of Original 
Protocol: 
04 Nov 2020 
CONFIDENTIAL  
All financial and nonfinancial support for this study will be provided by ModernaTX, Inc. The 
concepts and information contained in this document or generated during the study are 
considered proprietary and may not be disclosed in whole or in part without the expressed 
written consent of ModernaTX, Inc. The study will be conducted according to the 
International Council for Harmonisation (ICH) of Technical Requirements for Registration of 
Pharmaceuticals for Human Use, E6(R2) Good Clinical Practice (GCP) Guidance. 
NCT #: NCT04649151
PPD
PPD
PPD

ModernaTX, Inc. 
mRNA-1273-P203 Protocol Amendment 7 
mRNA-1273 
Confidential 
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PROTOCOL APPROVAL – SPONSOR SIGNATORIES  
Study Title: 
A Phase 2/3, Randomized, Observer-Blind, Placebo-Controlled 
Study to Evaluate the Safety, Reactogenicity, and Effectiveness of 
mRNA-1273 SARS-CoV-2 Vaccine in Healthy Adolescents 12 to 
<18 Years of Age 
Protocol Number: 
mRNA-1273-P203 
Amendment Number: 
7 
Amendment 7 Date: 
19 Oct 2023 
 
Protocol accepted and approved by: 
See e-Signature and date signed on 
the last page of the document. 
 
 
  
 
 
ModernaTX, Inc. 
200 Technology Square 
Cambridge, MA 02139 
Telephone: 
 
 
Date 
 
 
 
PPD
PPD

ModernaTX, Inc. 
mRNA-1273-P203 Protocol Amendment 7 
mRNA-1273 
Confidential 
Page 3 
DECLARATION OF INVESTIGATOR  
I have read and understood all sections of the protocol entitled “A Phase 2/3, Randomized, 
Observer-Blind, Placebo-Controlled Study to Evaluate the Safety, Reactogenicity, and 
Effectiveness of mRNA-1273 SARS-CoV-2 Vaccine in Healthy Adolescents 12 to <18 Years of 
Age” and the most recent version of the investigator’s brochure. 
I agree to supervise all aspects of the protocol and to conduct the clinical investigation in 
accordance with the current protocol, the International Council for Harmonisation (ICH) of 
Technical Requirements for Registration of Pharmaceuticals for Human Use, E6(R2) Good 
Clinical Practice (GCP) Guidance, and all applicable government regulations. I will not make 
changes to the protocol before consulting with ModernaTX, Inc. or implement protocol changes 
without IRB approval except to eliminate an immediate risk to participants. 
I agree to administer study treatment only to participants under my personal supervision or the 
supervision of a sub-investigator. I will not supply study treatment to any person not authorized 
to receive it. I also agree that persons debarred from conducting or working on clinical studies by 
any court or regulatory agency will not be allowed to conduct or work on studies for the Sponsor 
or a partnership in which the Sponsor is involved. I will immediately disclose it in writing to the 
Sponsor if any person who is involved in the study is debarred, or if any proceeding for 
debarment is pending, or, to the best of my knowledge, threatened. 
I will not disclose confidential information contained in this document including participant 
information, to anyone other than the recipient study staffs and members of the IRB. I agree to 
ensure that this information will not be used for any purpose other than the evaluation or conduct 
of the clinical investigation without the prior written consent from ModernaTX, Inc. I will not 
disclose information regarding this clinical investigation or publish results of the investigation 
without authorization from ModernaTX, Inc. 
The signature below provides the necessary assurance that this study will be conducted 
according to all stipulations of the protocol, including statements regarding confidentiality, and 
according to local legal and regulatory requirements, US federal regulations, and ICH E6(R2) 
GCP guidelines. 
 
Signature of principal investigator 
 
 
Date 
 
 
 
 
Printed name of principal investigator 
 
 
 

ModernaTX, Inc. 
mRNA-1273-P203 Protocol Amendment 7 
mRNA-1273 
Confidential 
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PROTOCOL AMENDMENT SUMMARY OF CHANGES  
DOCUMENT HISTORY 
Document 
Date 
Amendment 7 
19 Oct 2023 
Amendment 6 
22 Jun 2023 
Amendment 5 
11 Oct 2022 
Amendment 4 
25 Jan 2022 
Amendment 3 
04 Nov 2021 
Amendment 2 
27 Jul 2021 
Amendment 1 
23 Mar 2021 
Original Protocol 
04 Nov 2020 
Amendment 7, 19 Oct 2023: Current Amendment 
This amendment is considered to be substantial based on the criteria set forth in Article 10(a) of 
Directive 2001/20/EC of the European Parliament and the Council of the European Union. 
Main Rationale for the Amendment: 
Results of Part 3 IA demonstrate robust immunogenicity of a single 50 µg mRNA-1273.222 
dose. The pre-specified co-primary endpoints were also achieved, allowing inference of vaccine 
effectiveness of a single dose from the pivotal Study P301. Based on these results, Protocol 
Amendment 7 was initiated to remove Dose 2 administration of mRNA-1273.222 from Part 3. In 
addition, the safety of mRNA-1273 was demonstrated for both the 100 µg primary series given 
28 days apart as well as the 50 µg booster dose in Part 1 of this study, with a duration of at least 
6 months of follow-up. Further, extensive post-marketing experience with both mRNA-1273 and 
mRNA-1273.222 in adolescents has not identified any new safety concerns. Therefore, the safety 
follow-up duration for participants in Part 3 was reduced from 1 year to 6 months for those 
receiving a single dose and for those participants receiving Dose 2, from 6 months to 1 month 
following Dose 2. 
Summary of Major Changes in Protocol Amendment 7: 
The Summary of Changes table provided below describes the major changes made in Protocol 
Amendment 7 relative to Protocol Amendment 6, including the sections modified and the 
corresponding rationales. The synopsis of Protocol Amendment 7 has been modified to 
correspond to changes in the body of the protocol. Literature references were updated with the 
citation date. Minor copy edits and administrative updates were made throughout the protocol to 
align with new content as well as for clarity, readability, and/or accuracy. 
Section Number and Name 
Description of Change 
Brief Rationale 
Section 1.1 Study Rationale 
Addition of results for mRNA-1273.222. 
Updated section with the 
latest information. 
Section 1.2 Background and 
Overview 
Update in licensure/filing for the Moderna 
COVID-19 Vaccine. 
Updated section with the 
latest information. 

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mRNA-1273-P203 Protocol Amendment 7 
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Section Number and Name 
Description of Change 
Brief Rationale 
Section 1.2.2.5 Study 
mRNA-1273-P301 – Interim 
Results 
Addition of interim results from Part 3. 
Formatted as new subsection. 
Updated section with the 
latest data. 
Section 1.3.3 Overall 
Benefit/Rik Conclusion 
Addition of single dosing in Part 3. 
To stay consistent with 
updated Part 3 objectives. 
Section 2 Objectives and 
Endpoints, Table 3 
Objectives and Endpoints 
Removal of the Part 3 Dose 2 (6 months 
after Dose 1) including Day 209 endpoints 
associated with the Dose 2 administration. 
Updated study design 
after Part 3 IA. 
Section 3.1 General Design, 
Figure 1 Overall Design 
Schema 
Removal of the Part 3 Dose 2 (6 months 
after Dose 1). 
To stay consistent with 
updated Part 3 objectives. 
Reduced safety follow-up duration for 
Part 3 participants who receive Dose 2. 
Safety of mRNA-1273 
with a duration of at least 
6 months of follow-up 
has been demonstrated. 
Section 3.1.2 Part 2 Study 
Design 
Addition of booster vaccination in Part 2 
per Protocol Amendment 4.  
Addition of Figure 6. 
To stay consistent with 
updated Protocol 
Sections. 
Section 3.1.3 Part 3 Study 
Design 
Removal of the Part 3 Dose 2 (6 months 
after Dose 1), addition of interim results 
from Part 3 as rationale for removal of 
Dose 2, reduced safety follow-up duration 
for participants in Part 3 who receive 
Dose 2, updated Figure 7, and addition of 
Figure 8. 
To stay consistent with 
updated Part 3 objectives 
and updated Protocol 
Sections. 
Statement added that Part 3 participants 
who receive the updated COVID-19 
vaccine may remain in the P203 study after 
receipt of the nonstudy vaccine. 
For clarification. 
Section 3.2 Scientific 
rationale for Study Design 
Update in timepoints for collection of 
blood samples and NP or nasal swab 
samples. 
To stay consistent with 
updated Protocol 
Sections. 
Addition of IA results from Part 3 and 
reduced safety follow-up duration for 
participants in Part 3. 
To support updated 
Part 3 objectives and to 
stay consistent with 
updated Protocol 
Sections. 
Section 3.3 Justification for 
Dose, Control Product, and 
Choice of Study Population 
Addition of IA results from Part 3. 
Justification for updated 
Part 3 objectives. 
Section 3.4 End-of Study 
Definition 
Clarification of the end-of-study definition 
is the date when the last data are available. 
Clarifying the definition 
of the end-of-study 

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mRNA-1273-P203 Protocol Amendment 7 
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Section Number and Name 
Description of Change 
Brief Rationale 
Section 5.3.2 Administration 
of Study Vaccine 
Removal of the Part 3 Dose 2 (6 months 
after Dose 1). 
To stay consistent with 
updated Part 3 objectives. 
Addition of reference to new Tables with 
SoA. 
To stay consistent with 
updated Protocol 
Sections. 
Section 5.4 Study Treatment 
Compliance 
Addition of reference to new Tables with 
SoA. 
To stay consistent with 
updated Protocol 
Sections. 
Section 5.5.2 Concomitant 
Medications and Therapies, 
Section 5.5.3 Recording of 
Concomitant Medications 
and Concomitant 
Vaccinations 
Clarification added on the time period for 
recording all concomitant medications and 
nonstudy vaccinations in the eCRF. 
To stay consistent with 
the SoAs. 
Section 6.1.1 individual 
Participant Criteria for 
Delay of Study Vaccination, 
Section 7 Study 
Assessments and 
Procedures, Section 7.1.2 
Safety Telephone Calls, 
Section 7.1.4 Vital Sign 
Measurements, Section 7.1.5 
Physical Examinations, 
Section 7.1.6 Assessment for 
SARS CoV 2 Infection 
Addition of reference to new Tables related 
to single dosing in Part 3. 
To stay consistent with 
updated Protocol 
Sections. 
Section 7.1 Safety 
Assessments and Procedures 
Updated safety assessments related to 
single dosing in Part 3. 
To stay consistent with 
updated Part 3 objectives. 
Study-specific time points for safety 
assessments were removed and replaced 
with a reference to the SoAs. 
Study-specific time 
points are included in the 
SoAs. 
Section 7.1.1 Use of 
Electronic Diaries 
Adjustment of timepoints for Part 2 and 
Part 3. 
To stay consistent with 
updated Protocol 
Sections. 
Section 7.2 Immunogenicity 
Assessments 
Addition of reference to new Tables related 
to single dosing in Part 3. 
To stay consistent with 
updated Protocol 
Sections. 
Section 7.5.7 Eliciting and 
Documenting Adverse 
Events 
Removal of study-specific time points for 
collecting MAAEs and SAEs. 
To stay consistent with 
updated Protocol 
Sections. 
Section 8.4 Analysis Sets 
Day 209 removed from the PP 
Immunogenicity Subset for Part 3. 
To stay consistent with 
updated Part 3 objectives. 

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Section Number and Name 
Description of Change 
Brief Rationale 
Section 8.5.8 Part 3 Analysis Removal of the Part 3 Dose 2 related 
analysis. 
To stay consistent with 
updated Part 3 objectives. 
Section 8.7.1 Interim 
Analysis 
Adjusted the trigger for the IA due to the 
removal of the Part 3 Dose 2. 
To stay consistent with 
updated Part 3 objectives. 
Section 10.1 Appendix 1: 
Schedule of Assessments for 
Part 1B participants; 
Table 12, Footnote #5 
The time period for recording of 
concomitant medications and nonstudy 
vaccinations has been corrected. 
To stay consistent with 
the SoA and updated 
Protocol Sections. 
Section 10.1 Appendix 1: 
Schedule of Assessments, 
Table 15 
Addition of SoA for Part 2 participants 
who receive the booster dose. 
Added as per previous 
protocol clarification 
letter. 
Section 10.1 Appendix 1: 
Schedule of Assessments for 
Part 2 participants who do 
not receive the booster dose, 
Table 16 
Correction in the table footnote related to 
the time period for recording of 
concomitant medications and nonstudy 
vaccinations. 
Rearrangement of table footnotes. 
To stay consistent with 
the SoA. 
Section 10.1 Appendix 1: 
Schedule of Assessments for 
participants in Part 3 who 
receive Dose 2, Table 17 
Reduced safety follow-up duration. 
To stay consistent with 
updated Protocol 
Sections. 
Correction in the table footnote related to 
the time period for recording of 
concomitant medications and nonstudy 
vaccinations. 
Rearrangement of table footnotes. 
Section 10.1 Appendix 1: 
Schedule of Assessments, 
Table 18 
Addition of SoA for Part 3 participants 
who receive only 1 dose. 
To stay consistent with 
updated Part 3 objectives 
Abbreviations: COVID-19 = coronavirus disease 2019; eCRF = electronic case report form; IA = interim analysis; 
MAAE = medically attended adverse event; PP = per-protocol; SAE = serious adverse event; 
SARS- CoV2 = Severe Acute Respiratory Syndrome coronavirus 2; SoA = Schedule of Assessments. 
IRB and Regulatory Authority Approval 
A copy of this amended protocol will be sent to the IRB and regulatory authority. 
The changes described in this amended protocol require IRB approval prior to implementation. 
In addition, if the changes herein affect the informed consent, sites are required to update and 
submit a revised informed consent for approval that incorporates the changes described in this 
amended protocol. 

ModernaTX, Inc. 
mRNA-1273-P203 Protocol Amendment 7 
mRNA-1273 
Confidential 
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PROTOCOL SYNOPSIS  
Name of Sponsor/Company: ModernaTX, Inc. 
Name of Investigational Product: mRNA-1273 for injection  
Name of Active Ingredient: mRNA-1273 
Protocol Title: A Phase 2/3, Randomized, Observer-Blind, Placebo-Controlled Study to Evaluate the 
Safety, Reactogenicity, and Effectiveness of mRNA-1273 SARS-CoV-2 Vaccine in Healthy 
Adolescents 12 to <18 Years of Age 
Protocol Number: mRNA-1273-P203 
Study Period (months): Up to 25 months 
Phase of Development: Phase 2/3 
Estimated date first participant enrolled: 30 Nov 2020 
Estimated date last participant completed: 01 Aug 2024  
Total Number of Sites: Approximately 35 to 64 study sites in the USA or out of USA countries 
Part 1 Objectives and Endpoints 
Objectives 
Endpoints 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety and reactogenicity 
of 100 µg mRNA-1273 vaccine 
administered in 2 doses 28 days apart 
• 
Solicited local and systemic ARs through 
7 days after each injection 
• 
Unsolicited AEs through 28 days after each 
injection 
• 
MAAEs through the entire study period 
• 
SAEs through the entire study period 
• 
AESIs through the entire study period 
• 
Vital sign measurements 
• 
Physical examination findings 
• 
To infer efficacy of mRNA-1273 (100 µg, 
2 doses 28 days apart), serum Ab 
responses obtained 28 days after the 
second injection of mRNA-1273 (Day 57) 
will be either: 
− 
Evaluated against an accepted Ab 
threshold of protection against 
• 
The proportion of participants with a serum Ab 
level at Day 57 ≥ an Ab threshold of 
protection1 
• 
The primary vaccine response as measured by 
GM value of serum Ab level and SRR from 
Study P203 vaccine recipients at Day 57 
compared with those obtained from young 
adult recipients (18 to 25 years of age) at 

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COVID-19 (if established in 
Study P301) 
− 
Compared in primary vaccine 
response as measured by GM values 
of serum Ab and SRR in Study P203 
with those obtained from young adult 
recipients (18 to 25 years of age) of 
mRNA-1273 in the clinical endpoint 
efficacy trial (Study P301) 
Day 57 in the clinical endpoint efficacy trial 
(Study P301)2 
1. 
If an accepted serum Ab threshold of 
vaccine protection against COVID-19 is 
available, this analysis will form the basis 
to infer efficacy. 
2. 
If a threshold is not available, efficacy 
will be inferred based on establishing 
noninferiority of adolescent (12 to 
< 18 years; this clinical study) to adult 
GM values of serum Ab and SRR 
obtained in Study P301 (GM value 12 to 
< 18 years / GM value 18 to 25 years). 
Secondary Objectives 
Secondary Endpoints 
• 
To evaluate the persistence of the immune 
response of mRNA-1273 vaccine (100 µg) 
administered in 2 doses 28 days apart, as 
assessed by the level of SARS-CoV-2 
S2P-specific bAb through 1 year after 
Dose 2 
• 
The GM value of SARS-CoV-2 S2P-specific 
bAb on Day 1, Day 57 (1 month after Dose 2), 
Day 209 (6 months after Dose 2), and Day 394 
(1 year after Dose 2) 
• 
To evaluate the persistence of the immune 
response of mRNA-1273 vaccine (100 µg) 
administered in 2 doses 28 days apart, as 
assessed by the level of nAb through 
1 year after Dose 2 
• 
The GM values of SARS-CoV-2-specific nAb 
on Day 1, Day 57 (1 month after Dose 2), 
Day 209 (6 months after Dose 2), and Day 394 
(1 year after Dose 2)  
• 
To evaluate the effect of mRNA-1273 on 
the incidence of SARS-CoV-2 infection 
compared with the incidence among 
placebo recipients 
• 
The incidence of SARS-CoV-2 infection 
(symptomatic or asymptomatic infection) 
counted starting 14 days after the second dose 
of IP 
• 
SARS-CoV-2 infection will be defined in 
participants with negative SARS-CoV-2 at 
baseline: 
− 
bAb level against SARS-CoV-2 
nucleocapsid protein negative at Day 1 that 
becomes positive (as measured by Roche 
Elecsys) at Day 57 or later, OR 
− 
Positive RT-PCR counted starting 14 days 
after the second dose of IP 
• 
To evaluate the incidence of asymptomatic 
SARS-CoV-2 infection after vaccination 
with mRNA-1273 or placebo 
• 
The incidence of asymptomatic SARS-CoV-2 
infection measured by RT-PCR and/or bAb 
levels against SARS-CoV-2 nucleocapsid 
protein (by Roche Elecsys) counted starting 14 
days after the second dose of IP in participants 
with negative SARS-CoV-2 at baseline  
• 
To evaluate the incidence of COVID-19 
after vaccination with mRNA-1273 or 
• 
The incidence of the first occurrence of 
COVID-19 starting 14 days after the second 

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placebo. COVID-19 is defined as clinical 
symptoms consistent with SARS-CoV-2 
infection AND positive RT-PCR for 
SARS-CoV-2 
dose of IP, where COVID-19 is defined as 
symptomatic disease based on the following 
criteria: 
− 
The participant must have experienced at 
least TWO of the following systemic 
symptoms: Fever (≥ 38ºC/≥ 100.4ºF), 
chills, myalgia, headache, sore throat, new 
olfactory and taste disorder(s), OR 
− 
The participant must have experienced at 
least ONE of the following respiratory 
signs/symptoms: cough, shortness of 
breath or difficulty breathing, OR clinical 
or radiographical evidence of pneumonia; 
AND 
− 
The participant must have at least 1 NP 
swab, nasal swab, or saliva sample (or 
respiratory sample, if hospitalized) positive 
for SARS-CoV-2 by RT-PCR 
Exploratory Objectives 
Exploratory Endpoints 
• 
To evaluate the genetic and/or phenotypic 
relationships of isolated SARS-CoV-2 
strains to the vaccine sequence 
• 
Alignment of genetic sequence of viral isolates 
with that of the vaccine sequence and 
comparison of bAb and nAb titers against 
isolated strain relative to prototype vaccine 
strain 
• 
To describe the ratio or profile of specific 
bAb relative to nAb in serum 
• 
Relative amounts or profiles of 
S protein-specific bAb and specific nAb 
levels/titers in serum 
• 
To characterize the clinical profile and 
immune responses of participants with 
COVID-19 or with SARS-CoV-2 
infection 
• 
Description of clinical severity and immune 
responses of participants who are identified as 
infected by SARS-CoV-2 (COVID-19) 
• 
To evaluate the incidence of asymptomatic 
SARS-CoV-2 infection after vaccination 
with mRNA-1273 or placebo in 
participants with serologic evidence of 
infection at baseline 
• 
GM value and GMFR of bAb levels against 
SARS-CoV-2 nucleocapsid protein 
(quantitative IgG) and % of participants with 
2x, 3x, and 4x rise of bAb relative to baseline 
Exploratory Objectives for Part 1B: 
Exploratory Endpoints for Part 1B: 
• 
To evaluate the safety of 2 doses of 
mRNA-1273 
• 
MAAEs through the entire study period 
• 
SAEs through the entire study period 
• 
AESIs through the entire study period 
• 
AEs leading to discontinuation from study 
participation through the last day of study 
participation 

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• 
To evaluate the incidence of SARS-CoV-2 
infection or COVID-19 after vaccination 
with mRNA-1273 
• 
The incidence of SARS-CoV-2 infection 
(symptomatic or asymptomatic infection) 
counted starting 14 days after the second dose 
of mRNA-1273 
• 
To evaluate the incidence of asymptomatic 
SARS-CoV-2 infection after vaccination with 
mRNA-1273 measured by RT-PCR and/or 
bAb levels against SARS-CoV-2 nucleocapsid 
protein (by Roche Elecsys) counted starting 
14 days after the second dose in participants 
with negative SARS-CoV-2 at baseline 
• 
The incidence of the first occurrence of 
symptomatic COVID-19 starting 14 days after 
the second dose of mRNA-1273 
Objectives for Part 1C-1 – Homologous 
Booster Dose 
Endpoints for Part 1C-1 – Homologous Booster 
Dose 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety of the 50 μg BD of 
mRNA-1273 
• 
Solicited local and systemic ARs through 
7 days after BD 
• 
Unsolicited AEs through 28 days after BD 
injection 
• 
MAAEs through the entire study period 
• 
SAEs through the entire study period 
• 
AESIs through the entire study period 
• 
AEs leading to discontinuation from study 
participation post BD through the last day of 
study participation 
• 
To infer effectiveness of 50 μg of mRNA-
1273 booster by establishing 
noninferiority of Ab response after the BD 
compared to the primary series of 
mRNA-1273. GM values of serum Ab and 
SRR of postbooster in Study P203 
compared with primary series from young 
adult (18 to 25 years of age) recipients of 
mRNA-1273 in the clinical endpoint 
efficacy trial (Study P301) 
Coprimary endpoint(s): 
• 
GM value of postbooster (post Dose 3) Ab 
against ancestral strain in Study P203 as 
compared to post primary series (post Dose 2) 
against ancestral strain in the young adults in 
Study P301 
• 
SRR of postbooster/Dose 3 from baseline 
(pre Dose 1) as compared to post Dose 2 from 
baseline (pre Dose1) against ancestral strain in 
the young adults in Study P301, using 4-fold 
rise definition 
− 
Seroresponse is defined as Ab value 
change from baseline (pre Dose 1) below 
the LLOQ to ≥4 × LLOQ, or at least a 4-
fold rise if baseline is ≥LLOQ 

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Key Secondary Objective 
Key Secondary Endpoint 
• 
To evaluate immune response elicited by 
the 50 μg prototype booster of 
mRNA-1273 against variant(s) of interest 
• 
GM value of postbooster (post Dose 3) Ab 
against circulating strain as compared to post 
primary series (post Dose 2) against circulating 
strain 
• 
SRR of postbooster/Dose 3 from baseline 
(pre Dose 1) as compared to post Dose 2 from 
baseline (pre Dose 1) against circulating strain 
using 4-fold rise definition 
Exploratory Objectives 
Exploratory Endpoints 
• 
To evaluate the persistence of the immune 
response of the BD of mRNA-1273 
vaccine (50 µg) as assessed by the level of 
SARS-CoV-2 S2P specific bAb through 1 
year after BD 
• 
The GM values of SARS-CoV-2 S2P specific 
bAb on BD-Day 1, BD-Day 29 (1 month after 
BD), BD-Day 181 (6 months after BD), and 
BD-Day 361 (1 year after BD) 
• 
To evaluate the persistence of the immune 
response of the BD of mRNA-1273 
vaccine (50 µg) as assessed by the level of 
nAb through 1 year after BD 
• 
The GM values of SARS-CoV-2-specific nAb 
on BD-Day 1, BD-Day 29 (1 month after BD), 
BD-Day 181 (6 months after BD), and BD-
Day 361 (1 year after BD) 
• 
To evaluate the incidence of SARS-CoV-2 
infection or COVID-19 after vaccination 
with mRNA-1273 
• 
The incidence of SARS-CoV-2 infection 
(symptomatic or asymptomatic infection) 
counted starting 14 days after BD of 
mRNA-1273 
• 
To evaluate the incidence of asymptomatic 
SARS-CoV-2 infection after vaccination with 
mRNA-1273 measured by RT-PCR and/or 
bAb levels against SARS-CoV-2 nucleocapsid 
protein (by Roche Elecsys) counted starting 14 
days after BD in participants with negative 
SARS-CoV-2 at baseline or prebooster 
• 
The incidence of the first occurrence of 
symptomatic COVID-19 starting 14 days after 
BD of mRNA-1273 
Objectives for Part 1C-2 – Heterologous 
Booster Dose 
Endpoints for Part 1C-2 – Heterologous Booster 
Dose 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety of the 50 μg BD of 
mRNA-1273 in participants who received 
non-Moderna COVID-19 primary series 
vaccination 
• 
Solicited local and systemic ARs through 
7 days after BD 
• 
Unsolicited AEs through 28 days after BD 
injection 
• 
MAAEs through the entire study period 
• 
SAEs through the entire study period 
• 
AESIs through the entire study period 

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• 
AEs leading to discontinuation from study 
participation post BD through the last day of 
study participation 
• 
To evaluate immune response elicited by 
the 50 μg booster of mRNA-1273 in 
participants who received non-Moderna 
COVID-19 primary series vaccination 
• 
GM value of postbooster Ab (at BD-Day 29) 
against ancestral strain  
Key Secondary Objective 
Key Secondary Endpoint 
• 
To evaluate immune response elicited by 
the 50 μg prototype booster of 
mRNA-1273 against variant(s) of interest 
in participants who received non-Moderna 
COVID-19 primary series vaccination 
• 
GM value of postbooster Ab (at BD-Day 29) 
against circulating strain  
Exploratory Objectives 
Exploratory Endpoints 
• 
To evaluate the persistence of the immune 
response of the BD of mRNA-1273 
vaccine (50 µg) as assessed by the level of 
SARS-CoV-2 S2P specific bAb through 1 
year after BD in participants who received 
non-Moderna COVID-19 primary series 
vaccination 
• 
The GM values of SARS-CoV-2 S2P specific 
bAb on BD-Day 1, BD-Day 29 (1 month after 
BD), BD-Day 181 (6 months after BD), and 
BD-Day 361 (1 year after BD) 
• 
To evaluate the persistence of the immune 
response of the BD of mRNA-1273 
vaccine (50 µg) as assessed by the level of 
nAb through 1 year after BD in 
participants who received non-Moderna 
COVID-19 primary series vaccination 
• 
The GM values of SARS-CoV-2-specific nAb 
on BD-Day 1, BD-Day 29 (1 month after BD), 
BD-Day 181 (6 months after BD), and BD-
Day 361 (1 year after BD) 
• 
To evaluate the incidence of SARS-CoV-2 
infection or COVID-19 after booster 
vaccination with mRNA-1273 in 
participants who received non-Moderna 
COVID-19 primary series vaccination 
• 
The incidence of SARS-CoV-2 infection 
(symptomatic or asymptomatic infection) 
counted starting 14 days after BD of 
mRNA-1273 
• 
To evaluate the incidence of asymptomatic 
SARS-CoV-2 infection after vaccination with 
mRNA-1273 measured by RT-PCR and/or 
bAb levels against SARS-CoV-2 nucleocapsid 
protein (by Roche Elecsys) counted starting 14 
days after BD in participants with negative 
SARS-CoV-2 at baseline or prebooster 
• 
The incidence of the first occurrence of 
symptomatic COVID-19 starting 14 days after 
BD of mRNA-1273 
Abbreviations: Ab = antibody; AE = adverse event; AESI = adverse event of special interest; 
AR = adverse reaction; bAb = binding antibody; BD = booster dose; COVID-19 = coronavirus 
disease 2019; GM = geometric mean; GMFR = geometric mean fold rise; IgG = immunoglobulin G; 
IP = investigational product; LLOQ = lower limit of quantification; MAAE = medically attended 
adverse event; nAb = neutralizing antibody; NP = nasopharyngeal; RT-PCR = reverse transcriptase 

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polymerase chain reaction; S = spike; S2P = S protein; SAE = serious adverse event; 
SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2; SRR = seroresponse rate. 
Part 2 Objectives and Endpoints 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety and 
reactogenicity of the 50 μg 
mRNA-1273 vaccine administered in 2 
doses 28 days apart  
• 
Solicited local and systemic ARs through 7 days 
after each injection 
• 
Unsolicited AEs through 28 days after each 
injection 
• 
MAAEs through the entire study period 
• 
SAEs through the entire study period 
• 
AESIs through the entire study period 
• 
AEs leading to discontinuation from study 
participation from Dose 1 through the last day of 
study participation 
• 
To evaluate immune response elicited 
by the 50 μg mRNA-1273 vaccine 
administered in 2 doses 28 days apart 
• 
GM value of post Dose 2 (Day 57) Ab against 
ancestral strain in Part 2 of Study P203 
• 
SRR of post Dose 2 from baseline (pre Dose 1) in 
Part 2 of Study P203 against ancestral strain, 
using 4-fold rise definition 
− 
Seroresponse is defined as Ab value change 
from baseline (pre Dose 1) below the LLOQ 
to ≥4 × LLOQ, or at least a 4-fold rise if 
baseline is ≥LLOQ 
Exploratory Objectives 
Exploratory Endpoints 
• 
To evaluate the persistence of the 
immune response of 50 μg 
mRNA-1273 vaccine administered in 2 
doses 28 days apart as assessed by the 
level of SARS-CoV-2 S2P specific bAb 
through 1 year after Dose 2 
• 
The GM values of SARS-CoV-2 S2P specific 
bAb on Day 1, Day 57 (1 month after Dose 2), 
Day 209 (6 months from Dose 2), Day 394 
(1 year from Dose 2) 
• 
To evaluate the persistence of the 
immune response of the 50 μg 
mRNA-1273 vaccine as assessed by the 
level of nAb through 1 year after Dose 
2 
• 
The GM values of SARS-CoV-2-specific nAb on 
Day 1, Day 57 (1 month after Dose 2), Day 209 
(6 months from Dose 2), Day 394 (1 year from 
Dose 2) 
• 
To evaluate the incidence of 
SARS-CoV-2 infection or COVID-19 
after vaccination with mRNA-1273 
• 
The incidence of SARS-CoV-2 infection 
(symptomatic or asymptomatic infection) counted 
starting 14 days after Dose 2 of mRNA-1273 
• 
To evaluate the incidence of asymptomatic 
SARS-CoV-2 infection after vaccination with 
mRNA-1273 measured by RT-PCR and/or bAb 
levels against SARS-CoV-2 nucleocapsid protein 
(by Roche Elecsys) counted starting 14 days after 

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Dose 2 in participants with negative 
SARS-CoV-2 at baseline 
• 
The incidence of the first occurrence of 
symptomatic COVID-19 starting 14 days after 
Dose 2 of mRNA-1273 
Abbreviations: Ab = antibody; AE = adverse event; AESI = adverse event of special interest; AR = adverse 
reaction; bAb = binding antibody; COVID-19 = coronavirus disease 2019; GM = geometric mean; 
LLOQ = lower limit of quantification; MAAE = medically attended adverse event; nAb = neutralizing 
antibody; RT-PCR = reverse transcriptase polymerase chain reaction; S2P = S protein; SAE = serious adverse 
event; SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2; SRR = seroresponse rate. 
Part 3 Objectives and Endpoints 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety and 
reactogenicity of the 50 μg 
mRNA-1273.222 vaccine 
administered as 1 dose. 
• 
Solicited local and systemic ARs through 7 days 
after injection. 
• 
Unsolicited AEs through 28 days after injection. 
• 
MAAEs through the entire study period. 
• 
SAEs through the entire study period. 
• 
AESIs through the entire study period. 
• 
AEs leading to withdrawal from study participation 
from Dose 1 through the last day of study 
participation. 
• 
To infer effectiveness of the 50 µg 
mRNA-1273.222 vaccine based on 
immune response against 
SARS-CoV-2 VOC (Omicron 
BA.4/BA.5) and ancestral strain 
obtained 28 days post Dose 1 in the 
baseline SARS-CoV-2 positive 
population. 
• 
GM value of post Dose 1 (Day 29) of 
mRNA-1273.222 Ab against SARS-CoV-2 VOC 
(Omicron BA.4/BA.5) in adolescents who are 
baseline SARS-CoV-2 positive in Part 3 of 
Study P203 compared to that of post primary series 
of mRNA-1273 (post Dose 2 [Day 57] of 100 µg) 
in young adults 18 to 25 years of age who are 
baseline SARS-CoV-2 negative in Study P301 
(superiority testing). 
• 
GM value of post Dose 1 (Day 29) of 
mRNA-1273.222 Ab against ancestral strain in 
adolescents who are baseline SARS-CoV-2 positive 
in Part 3 of Study P203 compared to that of post 
primary series of mRNA-1273 (post Dose 2 
[Day 57] of 100 µg) in young adults 18 to 25 years 
of age who are baseline SARS-CoV-2 negative in 
Study P301 (noninferiority testing). 
Secondary Objectives 
Secondary Endpoints 

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• 
To evaluate immune response elicited 
by 50 µg mRNA-1273.222 vaccine 
administered as 1 dose based on 
immune responses against Omicron 
BA.4/BA.5 and ancestral strain 
obtained 28 days post Dose 1. 
• 
SRR of post Dose 1 (Day 29) from baseline 
(pre Dose 1) against Omicron BA.4/BA.5 in 
adolescents who are baseline SARS-CoV-2 positive 
in Part 3 of Study P203 compared to that of post 
primary series of mRNA-1273 (post Dose 2 
[Day 57] of 100 µg) in adults 18 to 25 years of age 
in Study P301.  
• 
SRR of post Dose 1 (Day 29) from baseline 
(pre Dose 1) against ancestral strain in adolescents 
who are baseline SARS-CoV-2 positive in Part 3 of 
Study P203 compared to that of post primary series 
of mRNA-1273 (post Dose 2 [Day 57] of 100 µg) 
in adults 18 to 25 years of age in Study P301. 
Note: Seroresponse is defined as an Ab value change 
from baseline (pre Dose 1) below the LLOQ to 
≥4 × LLOQ, or at least a 4-fold rise if baseline is 
≥LLOQ 
• 
To evaluate immune response elicited 
by 50 μg mRNA-1273.222 vaccine 
administered as 1 dose against other 
variant(s) of interest obtained 28 days 
post Dose 1. 
• 
GM value of post Dose 1 (Day 29) of 
mRNA-1273.222 Ab against other variant(s) of 
interest in Part 3 of Study P203 as compared to that 
of post primary series of mRNA-1273 (post Dose 2 
[Day 57] of 100 µg) in adults 18 to 25 years of age 
in Study P301. 
Exploratory Objectives 
Exploratory Endpoints 
• 
To evaluate the persistence of the 
immune response of 50 μg 
mRNA-1273.222 vaccine, as assessed 
by the level of SARS-CoV-2 S2P 
specific bAb through 6 months after 
Dose 1. 
• 
The GM values of SARS-CoV-2 S2P specific bAb 
on Day 1, Day 29 (1 month after Dose 1), Day 85 
(3 months after Dose 1), and Day 181 (6 months 
after Dose 1). 
• 
To evaluate the persistence of the 
immune response of the 50 μg 
mRNA-1273.222 vaccine as assessed 
by the level of nAb through 6 months 
after Dose 1. 
• 
The GM values of SARS-CoV-2-specific nAb on 
Day 1, Day 29 (1 month after Dose 1), Day 85 
(3 months after Dose 1), and Day 181 (6 months 
after Dose 1). 
• 
To evaluate the incidence COVID-19 
after vaccination with 
mRNA-1273.222. 
• 
The incidence of the first occurrence of 
symptomatic COVID-19 starting 14 days after 
Dose 1 of mRNA-1273.222. 
Abbreviations: Ab = antibody; AE = adverse event; AESI = adverse event of special interest; 
AR = adverse reaction; bAb = binding antibody; COVID-19 = coronavirus disease 2019; 
GM = geometric mean; LLOQ = lower limit of quantification; MAAE = medically attended adverse 
event; nAb = neutralizing antibody; RT-PCR = reverse transcriptase polymerase chain reaction; 
S2P = S protein; SAE = serious adverse event; SARS-CoV-2 = Severe Acute Respiratory Syndrome 
coronavirus 2; SRR = seroresponse rate; VOC = variant of concern. 
 

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Part 1 Overall Study Design 
This is a three-part, Phase 2/3, study: Part 1A, Part 1B, and Part 1C. The study will evaluate the safety, 
reactogenicity, and effectiveness of mRNA-1273 SARS-CoV-2 vaccine in healthy adolescents 12 to 
<18 years of age. 
Participants in Part 1A, the Blinded Phase, will be randomly assigned to receive injections of either 
100 µg mRNA-1273 vaccine or a placebo control in a 2:1 randomization ratio. Part 1B, the Open-label 
Observational Phase of this study, is designed to offer participants who received placebo in Part 1A of 
this study, and who meet Emergency Use Authorization (EUA) eligibility criteria, an option to receive 
mRNA-1273 in an open-label fashion. Part 1C-1, the Homologous Booster Dose Phase, is designed to 
offer participants in Part 1A and Part 1B who are at least 5 months from the last dose, the option to 
request a booster dose (BD) (50 µg) of mRNA-1273. Part 1C-2, the Heterologous Booster Phase, is 
designed to provide a BD (50 µg) of mRNA-1273 to eligible participants who completed primary 
coronavirus disease 2019 [COVID-19] vaccination series with a non-Moderna vaccine under EUA and 
are at least 3 months from the last dose. 
The goal of the study is to seek an indication for use of mRNA-1273 (100 µg intramuscular [IM], given 
as 2 injections, 28 days apart) in the 12 to < 18 years age group. The basis for demonstrating vaccine 
effectiveness is proposed to be met by serum antibody (Ab) response measured in this adolescent age 
group. The approach to inferring vaccine effectiveness will depend on whether an accepted serum Ab 
threshold conferring protection against COVID-19 has been established. If an Ab threshold of 
protection has been established, effectiveness will be inferred based on the proportion of adolescent 
study participants with serum Ab levels (on Day 57) that meet or exceed the Ab threshold. If an Ab 
threshold of protection has not been established, effectiveness will be inferred by demonstrating 
noninferiority of both the (i) geometric mean (GM) value of serum neutralizing antibody (nAb) and (ii) 
the seroresponse rate (SRR) from adolescent participants compared with those from young adults (18 
to 25 years of age) enrolled in the ongoing clinical endpoint efficacy trial (Study P301). 
Part 1A, the Blinded Phase - Randomized, Observer-Blind, Placebo-Controlled 
This study in adolescents will monitor all participants for a total of 12 months following the second 
dose of vaccine or placebo. Safety assessments will include solicited ARs; 7 days after each injection), 
unsolicited AEs; 28 days after each injection, medically attended adverse events (MAAEs), serious 
adverse events (SAEs), and adverse events of special interest (AESIs) including multisystem 
inflammatory syndrome in children [MIS-C]) throughout the study period. 
Blood samples will be collected from all participants at baseline (Day 1), Day 57 (28 days after 
Dose 2), Day 209 (6 months after Dose 2), and Day 394 for measurement of Severe Acute Respiratory 
Syndrome coronavirus 2 (SARS-CoV-2) specific binding antibody (bAb) and nAb responses. Blood 
samples will also be tested for the development of Ab directed against nonvaccine antigen (eg, Ab 
against the nucleocapsid protein), which will signify infection with SARS-CoV-2. 
The incidence of SARS-CoV-2 infection among vaccine recipients and placebo recipients will be 
compared to assess the potential for mRNA-1273 to reduce the rate of infection in vaccine recipients. 
Part 1A comprises 8 scheduled visits including a Screening Visit and 7 scheduled visits, of which Visit 
2 and Visit 4 will be virtual/telephone visits and the other visits will be in-clinic visits. This study will 
be conducted in compliance with the protocol, Good Clinical Practice (GCP), and all applicable 
regulatory requirements. 

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Part 1B, the Open-label Observational Phase 
Part 1B, the Open-label Observational Phase of the study, will be prompted by the authorization of a 
COVID-19 vaccine under an EUA for any persons under the age of 18 years. Participants will be 
transitioned to Part 1B of the study as their age group becomes EUA-eligible. This transition permits 
all ongoing study participants to eventually be informed of the availability and eligibility criteria of any 
COVID-19 vaccine made available under an EUA and the option to offer all ongoing study participants 
an opportunity to schedule a Participant Decision Visit to know their original treatment assignment 
(placebo vs. mRNA-1273 100 µg vaccine). 
Part 1B provides the opportunity for study participants to be informed regarding the EUA, be 
unblinded to their original assignment (mRNA-1273 or placebo), and for those who previously 
received placebo to actively request to receive 2 doses of mRNA-1273 (100 µg) vaccine. EUA-eligible 
study participants will receive a notification letter summarizing the basis for EUA of a COVID-19 
vaccine to receive an EUA and will be asked to schedule a Participant Decision Clinic Visit. 
At the Participant Decision Clinic Visit, EUA-eligible participants will: 
• 
Be given the option to be unblinded as to their original group assignment (placebo vs. 
mRNA-1273 vaccine [100 µg]), 
• 
Be counseled about the importance of continuing other public health measures to limit the 
spread of disease including social distancing, wearing a mask, and hand-washing, 
• 
Sign a revised informed consent form (ICF) and assent, and 
• 
Provide a nasopharyngeal (NP) or nasal swab for RT-PCR for SARS-CoV-2 and a blood 
sample for serology and immunogenicity. 
Participants that decline unblinding will remain in Part 1A and follow the Part 1A schedule of 
assessment (SoA). 
After the Participant Decision Clinic Visit, participants that consent to unblinding will follow the 
Part 1A SoA or Part 1B SoA as follows: 
• 
Participants received placebo in Part 1A and consent to receiving 2 doses of mRNA-1273 in 
Part 1B: These participants will proceed to Part 1B and follow the Part 1B SoA until BD is 
offered. 
• 
Participants received 2 doses of mRNA-1273 in Part 1A: Due to statistical considerations, 
these participants will be considered in the Open-label Observational Phase but will continue 
to follow the Part 1A SoA until BD is offered. 
Part 1C-1, Homologous Booster Dose Phase 
Part 1C-1 – Homologous Booster Dose Phase is designed to offer participants in Part 1A and Part 1B 
who are at least 5 months from the last dose, the option to request a BD (50 µg) of mRNA-1273. 
If eligible, each study participant will receive a notification letter and will be asked to schedule a BD-1 
Visit at their study site. Principal investigators should consider current local public health guidance for 
administration of COVID-19 vaccines under EUA and marketing authorization (if any) when 
determining the scheduling priority of participants. 
At the BD-1 Visit, each participant will: 

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• 
Be encouraged to remain in the ongoing study, 
• 
Sign a revised ICF that includes both updated safety information relevant to the ongoing study 
and a BD, and the option to receive a BD, 
• 
Be given the option to receive a BD consisting of a 50 μg dose of mRNA-1273, 
• 
Be counseled about the importance of continuing other public health measures to limit the 
spread of disease including social distancing, wearing a mask, and hand-washing. 
At the BD-1 Visit, participants who request a BD and are eligible will have the following study site 
visits and complete scheduled activities (subject to investigational vaccine availability) according to the 
Part 1C-1 Supplemental SoA: 
• 
BD-1 Visit: Participants will receive a single 50 μg dose of mRNA-1273, 
• 
BD-1a Visit: All participants who chose to receive BD, Day 4, 3 days after BD on Day 1, 
• 
BD-2 Visit: Day 29, 28 days after the BD on Day 1, 
• 
BD-3 Visit: Day 181, 180 days after the BD on Day 1, 
• 
BD-4 Visit: Day 361, 360 days after the BD on Day 1. 
Participants that crossed over from placebo to mRNA-1273 and decline BD will continue with Part 1B 
SoA. 
Participants that received mRNA-1273 in Part 1A and decline BD will continue with Part 1A SoA. 
The investigator is responsible for conducting all assessments as specified in the Part 1C-1 
Supplemental SoA, according to the schedule. As this Supplemental SoA is intended to occur in 
addition to the original SoAs being followed by all participants in Part 1A or Part 1B, there is a 
possibility for study visits to overlap (ie, Part 1C-1 BD-Day 1 and study visit in Part 1A or Part 1B that 
coincides with Part 1C-1 BD-Day 1). If visits overlap according to respective visit windows, a single 
visit may be done with the combined study procedures completed once. Any subject who consented to 
receive a BD will follow Part 1C-1 SoA. In case a study visit in Part 1A or Part 1B coincides with 
Part 1C-1 BD-Day 1, participant should follow Part 1C-1 SoA. 
Part 1C-2, - Heterologous Booster Phase 
Part 1C-2- Heterologous Booster Phase is designed to provide a BD (50 µg) of mRNA-1273 to eligible 
participants who completed primary COVID-19 vaccination series with a non-Moderna vaccine under 
EUA (ie, Pfizer) and are at least 3 months from the last dose. 
Non-Moderna COVID-19 Vaccine Available Under Emergency Use Authorization 
COVID-19 Vaccine – Primary Series 
Primary Series Number of Doses 
Pfizer-BioNTech 
2 doses 
Abbreviations: COVID-19 = coronavirus disease 2019. 

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Principal investigators should consider current local public health guidance for administration of 
COVID-19 vaccines under EUA and marketing authorization (if any) when determining the scheduling 
priority of participants. 
At the BD-0/BD-1 Visit, each participant will: 
• 
Sign an ICF, 
• 
Be counseled about the importance of continuing other public health measures to limit the 
spread of disease including social distancing, wearing a mask, and hand-washing. 
At the BD-1 Visit, participants will have the following study site visits and complete scheduled 
activities (subject to investigational vaccine availability) according to the Part 1C-2 Supplemental SoA: 
• 
BD-1 Visit: Participants will receive a single 50 μg dose of mRNA-1273, 
• 
BD-1a Visit: Day 4, 3 days after BD on Day 1, 
• 
BD-2 Visit: Day 29, 28 days after the BD on Day 1, 
• 
BD-3 Visit: Day 181, 180 days after the BD on Day 1, 
• 
BD-4 Visit: Day 361, 360 days after the BD on Day 1. 
The investigator is responsible for conducting all assessments as specified in the Part 1C-2 
Supplemental SoA, according to the schedule. 
Note: Due to the emergence of a more divergent variant of concern (ie. Omicron), Study Part 3 was 
initiated to replace the investigative product mRNA 1273 with a bivalent vaccine mRNA-1273.222. As 
a result of this amendment, Part 1C-2 enrollment was discontinued effective 16 August 2022. Booster 
dosing in the study was also discontinued and was reflected in Protocol Amendment 5. However, 
participants were permitted to receive the updated COVID-19 vaccine outside of the study and to 
continue study participation for safety follow-up. 
Part 2 Study Design 
Part 2 is an open-label design. The study will evaluate the safety, reactogenicity, and effectiveness of a 
50 μg primary series of mRNA-1273 SARS-CoV-2 vaccine in healthy adolescents 12 to < 18 years of 
age. 
This study in adolescents will monitor all participants for a total of 12 months following Dose 2 or 
booster dose (third dose) of vaccine. Safety assessments will include solicited ARs (7 days after each 
injection), unsolicited AEs (28 days after each injection), MAAEs, SAEs, and AESIs (including 
MIS-C) throughout the study period, and AEs leading to discontinuation from dosing and/or 
withdrawal from study. 
Blood samples will be collected from all participants at baseline (Day 1), Day 29, and at specified 
visits presented in Part 2 SoA for measurement of SARS-CoV-2 specific bAb and nAb responses. 
Blood samples will also be tested for the development of Ab directed against nonvaccine antigen (eg, 
Ab against the nucleocapsid protein), which will signify infection with SARS-CoV-2. Blood sample 
will be collected 3 days after Dose 2 or booster dose for future biomarker analysis (ie, inflammatory 
and/or cardiac biomarkers). 
The incidence of SARS-CoV-2 infection after mRNA-1273 vaccination will be evaluated. 

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Part 2 for participants who receive the booster dose comprises 13 scheduled visits including a 
Screening Visit and 12 scheduled visits, of which Visit 2, Visit 5, and Visit 9 will be virtual/telephone 
visits and the other visits will be in clinic visits. 
Part 2 for participants who do not receive the booster dose comprises 11 scheduled visits including a 
Screening Visit and 10 scheduled visits, of which Visit 2, Visit 5, and Visit 7 will be virtual/telephone 
visits and the other visits will be in-clinic visits. 
This study will be conducted in compliance with the protocol, GCP, and all applicable regulatory 
requirements. 
Note: Due to the emergence of a more divergent variant of concern (ie. Omicron), Study Part 3 was 
initiated to replace the investigative product mRNA 1273 with a bivalent vaccine mRNA-1273.222. As 
a result of this amendment, Part 2 enrollment was discontinued effective 16 August 2022. The booster 
administration (Protocol Amendment 4) was also removed and was reflected in the Protocol 
Amendment 5 SoA. Participants were permitted to receive the updated COVID-19 vaccine outside of 
the study and to continue study participation for safety follow-up. 
Part 3 Study Design 
Part 3 was initially designed as an open-label study to evaluate safety, reactogenicity, and effectiveness 
of a 2-dose 50 µg primary series of mRNA-1273.222 SARS-CoV-2 vaccine administered 6 months 
apart. An interim analysis was conducted which demonstrated robust immunogenicity of a single 50 µg 
mRNA-1273.222 dose. The pre-specified co-primary endpoints were also achieved allowing inference 
of vaccine effectiveness of a single dose of mRNA-1273.222 from the pivotal P301 study. Based on 
these results, the study design was amended to primarily evaluate the safety, reactogenicity, and 
effectiveness of a single dose 50 μg primary series of mRNA-1273.222 SARS-CoV-2 vaccine in at 
least 300 healthy adolescents 12 to <18 years of age. 
Safety follow-up in Part 3 participants who receive 1 dose of vaccine will be 6 months after dosing and 
participants who receive 2 doses will be followed for 1 month following Dose 2. Safety assessments 
will include solicited ARs (7 days after each injection), unsolicited AEs (28 days after each injection), 
MAAEs, SAEs, and AESIs (including MIS-C) throughout the study period and AEs leading to 
discontinuation from dosing and/or withdrawal from study. 
Blood samples for measurement of SARS-CoV-2 specific bAb and nAb responses will be collected 
from all participants at baseline (Day 1), Day 29 (28 days after Dose 1), Day 85 (3 months after 
Dose 1), and Day 181 (Dose 2 or 6 months after Dose 1 for participants who receive a single dose). An 
additional blood sample will be collected at Day 209 (1 month after Dose 2) for participants who 
receive Dose 2. Blood samples will also be tested for the development of Ab directed against 
nonvaccine antigen (eg, Ab against the nucleocapsid protein), which will signify infection with SARS-
CoV-2. Blood samples will be collected 3 days after Dose 1 and 3 days after Dose 2 (Day 184), for 
future biomarker analysis (ie, inflammatory and/or cardiac biomarkers). 
The incidence of SARS-CoV-2 infection after mRNA-1273.222 vaccination will be evaluated. 

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Safety Oversight: 
Safety oversight will be under the direction of a Data Safety Monitoring Board (DSMB) composed of 
external independent consultants with relevant expertise. 
An independent cardiac event adjudication committee (CEAC) of medically qualified personnel, 
including cardiologists, will review all suspected cases of myocarditis and pericarditis to determine if 
they meet CDC criteria of “probable” or “confirmed” events which are reported in ongoing 
interventional clinical trials per the CEAC charter. Any case that the CEAC assesses as representing 
probable or confirmed cases of myocarditis or pericarditis will be referred to the Sponsor, who will 
then determine if additional action is needed. 
The CEAC will operate under the rules of an approved charter that will be written and reviewed at the 
organizational meeting of the CEAC. Details regarding the CEAC composition, responsibilities, 
procedures, and frequency of data review will be defined in its charter. 
The contract research organization (CRO’s) medical monitor, the Sponsor’s medical monitor, and the 
individual study site investigators will monitor safety throughout the study. 
Study Duration: 
Part 1 
Participants who received mRNA-1273 in Part 1A will be in the study approximately 25 months total if 
a BD is received in Part 1C-1, which includes 1 month for Screening (Day ˗28 to Day 1), up to 
12 months for dosing (on Day 1, Day 29, and Day 209 for BD), and 12 months for follow-up. 
Participants who received placebo in Part 1A will be in the study for approximately 25 months total if 
BD is received in Part 1C-1, which includes approximately 9 months in Part 1A, approximately 
4 months of follow-up following their second dose of mRNA-1273 in Part 1B before entering Part 
1C-1 or before BD is received; or approximately 12 months of follow-up. 
Participants that decline unblinding or decline to receive a BD will be in the study approximately 
14 months total, which includes 1 month for Screening (Day -28 to Day 1), 1 month for dosing (on 
Day 1 and Day 29), and 12 months for follow-up. 
Participants in Part 1C-2 will be in the study for approximately 12 months total, which includes 7 days 
for Screening (Day -7 to Day 1), 1 day of dosing (BD-Day 1), and 12 months of follow-up. 
Part 2 
Participants who receive the booster dose of mRNA-1273 in Part 2 will be in the study approximately 
17 months, which includes 1 week for screening (Day ˗7 to Day 1), 4 months for dosing (on Day 1, 
Day 29, and Day 149), and 12 months of follow-up after the booster dose. 
Participants who do not receive the booster dose of mRNA-1273 in Part 2 will be in the study 
approximately 12 months, which includes 1 week for Screening (Day ˗7 to Day 1), 1 month for dosing 
(on Day 1 and Day 29), and 12 months of follow-up after Dose 2. 
Part 3 
Participants who receive 2 doses of mRNA-1273.222 in Part 3 will be in the study for approximately 
7 months including 1 week for Screening (Day -7 to Day -1), 6 months for dosing (Day 1 to Day 181), 

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and 1 month of follow-up after Dose 2. Participants who receive a single dose of mRNA-1273.222 in 
Part 3 will be in the study for approximately 6 months including 1 week for Screening (Day -7 to 
Day -1), dosing (Day 1), and 6 months of follow-up after dosing. 
Number of Participants: 
Part 1A (Blinded Phase) – Approximately 3,000 participants will be enrolled. 
Part 1C-2 (Heterologous Booster Phase) – Approximately 362 participants will be enrolled. 
Part 2 – Approximately 362 participants will be enrolled. 
Part 3 – Approximately at least 300 participants will be enrolled. 
Study Eligibility Criteria (Part 1A, Part 2, and Part 3): 
Inclusion Criteria: 
Each participant must meet all of the following criteria at the Screening Visit (Day 0) or at Day 1, 
unless noted otherwise, to be enrolled in this study: 
1. Male or female, 12 to < 18 years of age at the time of consent (Screening Visit, Day 0) who, in 
the opinion of the investigator, is in good general health based on review of medical history 
and Screening physical examination. 
2. Investigator assessment that the participant, in the case of an emancipated minor, or 
parent(s)/legally accepted representative (LAR) understand and are willing and physically able 
to comply with protocol-mandated follow-up, including all procedures and provides written 
informed consent/assent. 
3. Body mass index (BMI) at or above the third percentile according to WHO Child Growth 
Standards at the Screening Visit (Day 0). 
4. Female participants of nonchildbearing potential may be enrolled in the study. 
Nonchildbearing potential is defined as premenarche or surgically sterile (history of bilateral 
tubal ligation, bilateral oophorectomy, hysterectomy). 
5. Female participants of childbearing potential may be enrolled in the study if the participant 
fulfills all the following criteria: 
• 
Has a negative pregnancy test at Screening (Day 0), on the day of the first injection 
(Day 1), and on the day of the second injection (Day 29 in Part 1 A and Part 2, and 
Day 181 in Part 3). 
• 
Has practiced adequate contraception or has abstained from all activities that could result 
in pregnancy for at least 28 days prior to the first injection (Day 1). 

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6. Has agreed to continue adequate contraception or abstinence through 3 months following the 
second injection (Day 29 in Part 1 A and Part 2, and Day 181 in Part 3). 
Adequate female contraception is defined as consistent and correct use of approved contraceptive 
method in accordance with the product label. 
Exclusion Criteria: 
Participants who meet any of the following criteria at the Screening Visit (Day 0) or at Day 1, unless 
noted otherwise, will be excluded from the study: 
1. Has a known history of SARS-CoV-2 infection within 2 weeks prior to administration of 
investigational product (IP) or known close contact with anyone with laboratory-confirmed 
SARS-CoV-2 infection of COVID-19 within 2 weeks prior to administration of IP (Part 2 
participants only). For Part 3 participants, known history of SARS-CoV-2 infection within 
90 days prior to administration of IP or known close contact with anyone with 
laboratory-confirmed SARS-CoV-2 infection or COVID-19 within 90 days prior to 
administration of IP. 
2. Travel outside of the USA or home country (Part 2 and Part 3 only) in the 28 days prior to the 
Screening Visit (Day 0). 
3. Pregnant or breastfeeding. 
4. Is acutely ill or febrile 24 hours prior to or at the Screening Visit (Day 0). Fever is defined as a 
body temperature ≥ 38.0°C/≥ 100.4°F. Participants who meet this criterion may have visits 
rescheduled within the relevant study visit windows. Afebrile participants with minor illnesses 
can be enrolled at the discretion of the investigator. 
5. Prior administration of an investigational CoV (eg, SARS-CoV-2, Middle East Respiratory 
Syndrome [MERS]-CoV) vaccine. 
6. Current treatment with investigational agents for prophylaxis against COVID-19. 
7. Has a medical, psychiatric, or occupational condition that may pose additional risk as a result 
of participation, or that could interfere with safety assessments or interpretation of results 
according to the investigator’s judgment. 
8. Current use of any inhaled substance (eg, tobacco or cannabis smoke, nicotine vapors). 
9. History of chronic smoking (≥ 1 cigarette a day) within 1 year of the Screening Visit (Day 0). 
10. History of illegal substance use or alcohol abuse within the past 2 years. This exclusion does 
not apply to historical cannabis use that was formerly illegal in the participant’s state but is 
legal at the time of Screening. 
11. History of a diagnosis or condition that, in the judgment of the investigator, may affect study 
endpoint assessment or compromise participant safety, specifically: 
• 
Congenital or acquired immunodeficiency, including human immunodeficiency virus 
(HIV) infection. 
• 
Suspected active hepatitis. 

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• 
Has a bleeding disorder that is considered a contraindication to IM injection or 
phlebotomy. 
• 
Dermatologic conditions that could affect local solicited AR assessments. 
• 
History of anaphylaxis, urticaria, or other significant AR requiring medical intervention 
after receipt of a vaccine. 
• 
Diagnosis of malignancy within the previous 10 years (excluding nonmelanoma skin 
cancer). 
• 
Febrile seizures. 
12. Receipt of: 
• 
Any licensed vaccine within 28 days before the first dose of IP or plans for receipt of any 
licensed vaccine within 28 days before and/or after each dose of IP. 
• 
Systemic immunosuppressants or immune-modifying drugs for > 14 days in total within 
6 months prior to the day of enrollment (for corticosteroids, ≥ 20 mg/day prednisone 
equivalent). Topical tacrolimus is allowed if not used within 14 days prior to the day of 
enrollment. Participants may have visits rescheduled for enrollment if they no longer meet 
this criterion within the Screening Visit window. Inhaled, nasal, and topical steroids are 
allowed. 
• 
Intravenous blood products (red cells, platelets, immunoglobulins) within 3 months prior to 
enrollment. 
13. Has donated ≥450 mL of blood products within 28 days prior to the Screening Visit (Day 0) or 
plans to donate blood products during the study. 
14. Participated in an interventional clinical study within 28 days prior to the Screening Visit 
(Day 0) or plans to do so while participating in this study. 
15. Is an immediate family member or has a household contact who is an employee of the research 
center or otherwise involved with the conduct of the study. 
Study Eligibility Criteria (Part 1B): 
1. Participants must have been previously enrolled in the mRNA-1273-P203 study. 
2. Female participants of childbearing potential may be enrolled in the study if the participant has 
a negative pregnancy test on the day of the first injection (OL-Day 1) and on the day of the 
second injection (OL-Day 29). 
Study Eligibility Criteria (Part 1C-1- Homologous Booster Dose): 
Inclusion Criteria: 
1. Participants must have been previously enrolled in the mRNA-1273-P203 study, are actively 
participating in Part 1A or Part 1B, and are at least 5 months from the last dose. 
2. Female participants of childbearing potential may be enrolled in the study if the participant has 
a negative pregnancy test on the day of the first injection (BD-Day 1). 

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Exclusion Criteria: 
1. Pregnant or breastfeeding. 
2. Is acutely ill or febrile 24 hours prior to or at the Screening Visit (Day 0). Fever is defined as a 
body temperature ≥38.0°C/≥100.4°F. Participants who meet this criterion may have visits 
rescheduled within the relevant study visit windows. Afebrile participants with minor illnesses 
can be enrolled at the discretion of the investigator. 
3. Has a medical, psychiatric, or occupational condition that may pose additional risk as a result 
of participation, or that could interfere with safety assessments or interpretation of results 
according to the investigator’s judgment. 
4. History of a diagnosis or condition (after enrollment in Part 1A) that, in the judgment of the 
investigator, may affect study endpoint assessment or compromise participant safety: 
• 
Suspected active hepatitis. 
• 
Has a bleeding disorder that is considered a contraindication to IM injection or 
phlebotomy. 
• 
Dermatologic conditions that could affect local solicited AR assessments. 
• 
History of anaphylaxis, urticaria, or other significant AR requiring medical intervention 
after receipt of a vaccine. 
• 
Diagnosis of malignancy (excluding nonmelanoma skin cancer). 
5. Receipt of: 
• 
Any authorized or licensed vaccine within 28 days before the first dose of IP or plans for 
receipt of any licensed vaccine through 28 days following the last dose of IP 
(authorized/approved bivalent vaccine against SARS-CoV-2 as 4th BD is not 
exclusionary); OR 
• 
Any seasonal influenza vaccine within 14 days before the first dose of IP or plans for 
receipt of any seasonal influenza vaccine 14 days following the last dose of IP. 
6. Participated in an interventional clinical study, other than mRNA-1273-P203 study, within 
28 days prior to the Screening Visit (Day 0) or plans to do so while participating in this study. 
Study Eligibility Criteria (Part 1C-2 – Heterologous Booster Dose): 
Inclusion Criteria: 
1. Male or female, 12 to < 18 years of age at the time of consent who, in the opinion of the 
investigator, is in good general health based on review of medical history and Screening 
physical examination AND has completed non-Moderna primary COVID-19 vaccination series 
under EUA (ie, Pfizer) at least 3 months from consent. 
2. Investigator assessment that the participant, in the case of an emancipated minor, or 
parent(s)/LAR understand and are willing and physically able to comply with 
protocol-mandated follow-up, including all procedures and provides written informed 
consent/assent. 

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3. BMI at or above the third percentile according to WHO Child Growth Standards at the 
Screening Visit (BD-Day 0). 
4. Female participants of nonchildbearing potential may be enrolled in the study. 
Nonchildbearing potential is defined as premenarche or surgically sterile (history of bilateral 
tubal ligation, bilateral oophorectomy, hysterectomy). Female participants of childbearing 
potential may be enrolled in the study if the participant has a negative pregnancy test on the 
day of the first injection (BD-Day 1) and has agreed to continue adequate contraception or 
abstinence through 3 months following BD (BD-Day 1). 
Exclusion Criteria: 
1. Has a known history of SARS-CoV-2 infection within 2 weeks prior to administration of IP or 
known close contact with anyone with laboratory-confirmed SARS-CoV-2 infection or 
COVID-19 within 2 weeks prior to administration of IP. 
2. Pregnant or breastfeeding. 
3. Is acutely ill or febrile 24 hours prior to or at the Screening Visit (BD-Day 0). Fever is defined 
as a body temperature ≥38.0°C/≥100.4°F. Participants who meet this criterion may have visits 
rescheduled within the relevant study visit windows. Afebrile participants with minor illnesses 
can be enrolled at the discretion of the investigator. 
4. Has a medical, psychiatric, or occupational condition that may pose additional risk as a result 
of participation, or that could interfere with safety assessments or interpretation of results 
according to the investigator’s judgment. 
5. History of a diagnosis or condition that, in the judgment of the investigator, may affect study 
endpoint assessment or compromise participant safety: 
• 
Suspected active hepatitis 
• 
Has a bleeding disorder that is considered a contraindication to IM injection or phlebotomy 
• 
Dermatologic conditions that could affect local solicited AR assessments 
• 
History of anaphylaxis, urticaria, or other significant AR requiring medical intervention 
after receipt of a vaccine 
• 
Diagnosis of malignancy (excluding nonmelanoma skin cancer) 
6. Receipt of: 
• 
Any authorized or licensed vaccine within 28 days before the first dose of IP (monovalent 
COVID-19 primary series vaccines are not exclusionary) or plans for receipt of any 
licensed vaccine through 28 days following the last dose of IP (monovalent COVID-19 
primary series vaccines as well as authorized/approved bivalent vaccine against 
SARS-CoV-2 as 4th booster are not exclusionary) or any seasonal influenza vaccine within 
14 days before the first dose of IP or plans for receipt of any seasonal influenza vaccine 
14 days following the last dose of IP. 

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7. Participated in an interventional clinical study, other than mRNA-1273-P203 study, within 
28 days prior to the Screening Visit (BD-Day 0) or plans to do so while participating in this 
study. 
Study Treatment: 
Investigational Product: 
The IP (mRNA-1273 vaccine) is a lipid nanoparticle (LNP) dispersion of a mRNA encoding the 
prefusion stabilized spike (S) protein of SARS-CoV-2 formulated in LNPs composed of 4 lipids 
(1 proprietary and 3 commercially available): the proprietary ionizable lipid SM-102; cholesterol; 
1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC); and 1-monomethoxypolyethyleneglycol-2,3-
dimyristylglycerol with PEG2000-DMG. mRNA-1273 injection is provided as a sterile liquid for 
injection, white to off-white dispersion in appearance, at a concentration of 0.5 mg/mL in 20 mM Tris 
buffer containing 87 mg/mL sucrose and 10.7 mM sodium acetate at pH 7.5 For Part 1A and Part 1B, 
each injection will have a volume of 0.5 mL and contain mRNA-1273 100 µg. For Part 1C-1, 
Part 1C-2, and Part 2, each injection will have a volume of 0.25 mL and contain mRNA-1273 50 µg. 
The Sponsor initiated the development of modified COVID-19 vaccine leveraging the mRNA/LNP 
technology platform against SARS-CoV-2 variant, which incorporates key mutations present in 
Omicron subvariants BA.4/BA.5. The vaccine IP, mRNA-1273.222, contains 2 mRNAs: CX-024414 
encoding for the S-2P of Wuhan-Hu-1 and CX-034476 encoding for the S-2P of Omicron subvariants 
BA.4/BA.5. 
mRNA-1273.222 will be provided as a sterile solution for injection at a concentration of 0.1 mg/mL in 
20 mM Tris buffer with sucrose, at pH 7.5. The solution will be kept in 2R USP Type I borosilicate 
glass vials with PLASCAP vial seal containing a 13 mm FluroTec-coated plug stopper with a 0.8 mL 
nominal fill volume. For Part 3, each injection preparation will have a volume of 0.5 mL and contain 
50 µg mRNA-1273.222. 
Mode of Administration: 
Doses will be administered by IM injection into the deltoid muscle according to the procedures 
specified in the mRNA-1273-P203 Pharmacy Manual. Preferably, all doses should be administered into 
the nondominant arm. 
Procedures and Assessments: 
Safety Assessments: 
Safety assessments will include monitoring and recording of the following for each participant: 
• 
Solicited local and systemic ARs that occur during the 7 days following each injection (ie, 
the day of injection and 6 subsequent days) in Part 1A, Part 1C, Part 2, and Part 3. 
Solicited ARs will be recorded daily using electronic diaries (eDiaries) 
• 
Unsolicited AEs observed or reported during the 28 days following each injection (ie, the 
day of injection and 27 subsequent days) in Part 1A, Part 1C, Part 2, and Part 3 
• 
AEs leading to discontinuation from dosing (except for participants who receive a single 
dose in Part 3) and/or withdrawal from study participation from Day 1 through the last day 
of study participation in Part 1A, Part 1B, Part 1C, Part 2, and Part 3 

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• 
MAAEs from first dose on Day 1 through the entire study period in Part 1A, Part 1B, 
Part 1C, Part 2, and Part 3 
• 
SAEs from first dose on Day 1 through the entire study period in Part 1A, Part 1B, Part 1C, 
Part 2, and Part 3 
• 
AESIs through the entire study period in Part 1A, Part 1B, Part 1C, Part 2, and Part 3 
• 
Vital sign measurements 
• 
Physical examination findings 
• 
Assessments for SARS-CoV-2 infection from Day 1 through study completion 
• 
Details of all pregnancies in female participants will be collected after the start of study 
treatment and until the end of their participation in the study 
Immunogenicity Assessments: 
The following analytes will be measured in blood samples for immunogenicity assessments: 
• 
Serum nAb level against SARS-CoV-2 as measured by pseudovirus and/or live virus 
neutralization assays 
• 
Serum bAb levels against SARS-CoV-2 as measured by a multiplex serology assay 
specific to the SARS-CoV-2 S, N, RBD protein. 
Serum collected from all participants will be tested for bAb against SARS-CoV-2 nucleocapsid protein 
at specified timepoints. In addition, serum samples from a selected subset of study participants who 
received mRNA-1273 or mRNA-1273.222 will be selected for testing of nAb and bAb against the 
SARS-CoV-2 S protein. 
Exploratory Assessments and Biomarkers: 
Exploratory assessments may include assessment of biomarkers for safety, reactogenicity, 
inflammatory and cardiac function. Serologic markers of disease severity, immune response to 
SARS-CoV-2, RT-PCR of NP or nasal swab or saliva samples, and genetic sequences of SARS-CoV-2 
strains isolated from participants’ samples may also be measured. 
Efficacy Assessments: 
Vaccine effectiveness for adolescents of ages of 12 to < 18 years will be inferred based on serum Ab 
responses obtained on Day 57 (28 days after the second injection of mRNA-1273) and Day 209 
(28 days after the second injection of mRNA1273.222). Inference will be based on assessing the 
adolescent Ab responses against the following: 
• 
If available at the time of analysis, adolescent Ab responses will be assessed against an 
accepted serum Ab threshold conferring protection against COVID-19. 
• 
If an accepted threshold of protection is not available, adolescent Ab responses will be 
assessed by establishing noninferiority of the GM value and SRR of serum nAb from 
adolescent participants compared with those from young adults enrolled in the ongoing 
clinical endpoint efficacy trial (Study P301). 

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Statistical Methods: 
Part 1 
Hypothesis Testing (Part 1A) 
If an accepted serum Ab threshold of protection against COVID-19 is established for the primary 
immunogenicity objective, the null hypothesis is that the percentage of participants on mRNA-1273 
with serum Ab equal to or above the established threshold at Day 57 is ≤70% (ie, H0: percentage of 
participants on mRNA-1273 ≤70% with serum Ab at Day 57 equal to or above the established 
threshold). 
The study would be considered as meeting the immunogenicity objective if the 95% confidence 
interval (CI) of percentage of participants on mRNA-1273 rules out 70% (lower bound of the 95% CI 
>70%). 
If an accepted serum Ab threshold of protection against COVID-19 is not available for the primary 
immunogenicity objective, the immunogenicity analysis of primary vaccine response will be performed 
using the noninferiority tests of the 2 null hypotheses based on the 2 coprimary endpoints, respectively. 
Coprimary endpoint 1: Ab GM value at Day 57 
H10: immunogenicity response to mRNA-1273 as measured by Ab GM at Day 57 is inferior in 
adolescents (12 to < 18 years of age) compared with that in young adults (18 to 25 years of age) using 
mRNA-1273 Study P301 data. 
The noninferiority in Ab GM in adolescents compared with that in young adults (18 to 25 years of age) 
is demonstrated by that the lower bound of the 95% CI of the GM ratio (GMR) rules out 0.667 (lower 
bound >0.667) using a noninferiority margin of 1.5. The GMR is the ratio of the GM value of 
adolescents on mRNA-1273 in this study, Study P203, at Day 57 compared with the GM value of 
young adults (18 to 25 years of age) on mRNA-1273 in Study P301. 
Coprimary endpoint 2: Ab seroresponse rate at Day 57 
A definition of seroresponse will be provided in the SAP based on forthcoming information about 
assay performance. 
The null hypothesis: 
H20: immunogenicity response to mRNA-1273 as measured by seroresponse rate at Day 57 is inferior 
in adolescents (12 to <18 years of age) compared with that in young adults (18 to 25 years of age) 
using mRNA-1273 Study P301 data. 
The noninferiority in seroresponse rate in adolescents compared with that in young adults (18 to 
25 years of age) is demonstrated by that the lower bound of the 95% CI of the seroresponse rate 
difference rules out -10% (ie, lower bound >-10%) using the noninferiority margin of 10%. The 
seroresponse rate difference is defined as the rate in adolescents receiving mRNA-1273 minus the rate 
in young adults (18 to 25 years of age) receiving mRNA-1273 from Study P301. 
The study would be considered as meeting the primary immunogenicity objective if noninferiority is 
demonstrated based on both coprimary endpoints. 
Details regarding the assay to be used to assess noninferiority will be provided in the SAP. 

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Power and Sample Size 
The sample size of this study is driven by safety. Approximately 3,000 participants will be randomly 
assigned in a 2:1 ratio to receive mRNA-1273 or placebo. With 2,000 participants exposed to 
mRNA‑1273, the study has at least 90% probability to observe at least 1 participant with an AE at a 
true 0.25% AE rate. 
Serum samples from all participants will be collected and banked, a subset of participants will be 
selected, and their samples will be processed for immunogenicity testing (the Immunogenicity Subset). 
Approximately 362 participants who receive mRNA-1273 will be selected for the Immunogenicity 
Subset, with a target of 289 participants receiving mRNA-1273 in the per-protocol (PP) 
Immunogenicity Subset (adjusting for approximately 20% of participants who may be excluded from 
the PP Immunogenicity Subset, as they may not have immunogenicity results due to any reason). The 
sample size of the Immunogenicity Subset may be updated with data from other mRNA-1273 studies 
or external data especially regarding a threshold of protection. In such a situation, the final sample size 
of the Immunogenicity Subset will be documented in the SAP. 
For the primary immunogenicity objective, with approximately 289 participants in the PP 
Immunogenicity Subset, the study will have > 90% power to rule out 70% with a 2-sided 95% CI for 
the percentage of mRNA-1273 participants exceeding the acceptable threshold if the true rate of 
participants exceeding the acceptable threshold is 80%. 
If an acceptable Ab threshold of protection against COVID-19 is not available at the time of analysis, 
for the primary immunogenicity objective, noninferiority tests of 2 null hypotheses based on 2 
coprimary endpoints, respectively, will be performed. The sample size calculation for each of the 2 
noninferiority tests was performed, and the larger sample size was chosen for the study. 
• 
With approximately 289 participants in the PP Immunogenicity Subset in Study P203 and 
289 participants in the PP Immunogenicity Subset in young adults (18 to 25 years of age) 
from Study P301, there will be 90% power to demonstrate noninferiority of the immune 
response as measured by Ab GM in adolescents in Study P203 at a 2-sided α of 0.05, 
compared with that in young adults (18 to 25 years of age) from Study P301 receiving 
mRNA-1273, assuming an underlying GMR value of 1 and a noninferiority margin of 1.5. 
The SD of the log‑transformed levels is assumed to be 1.5. 
• 
With approximately 289 participants in the PP Immunogenicity Subset in Study P203 and 
289 participants in the PP Immunogenicity Subset in young adults (18 to 25 years of age) 
from Study P301, there will be at least 90% power to demonstrate noninferiority of the 
immune response as measured by seroresponse rate in adolescents in Study P203 at a 
2-sided α of 0.05, compared with that in young adults of (18 to 25 years of age) from Study 
P301 receiving mRNA-1273, assuming true seroresponse rate of 85% in young adults (18 
to 25 years of age) from Study P301, and a true seroresponse rate of 85% in adolescents in 
Study P203 (ie, true rate difference is 0 compared to young adults [18 to 25 years of age] 
from Study P301), and a noninferiority margin of 10%. 
Safety Analyses 
All safety analyses will be based on the Safety Set, except summaries of solicited ARs, which will be 
based on the Solicited Safety Set. All safety analyses will be provided by treatment group. 

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Safety and reactogenicity will be assessed by clinical review of all relevant parameters including 
solicited ARs (local and systemic events), unsolicited AEs, SAEs, MAAEs, AESI, AEs leading to 
withdrawal, vital sign measurements, and physical examination findings. The number and percentage 
of participants with any solicited local AR, with any solicited systemic AR, and with any solicited AR 
during the 7-day follow-up period after each injection (except Part 1B) will be summarized. 
The number and percentage of participants with any solicited local AR, with any solicited systemic 
AR, and with any solicited AR during the 7-day follow-up period after each dose (except Part 1B) will 
be provided. A 2-sided 95% exact CI using the Clopper-Pearson method will also be provided for the 
percentage of participants with any solicited AR. 
The number and percentage of participants with unsolicited AEs, SAEs, MAAEs, Grade 3 or higher 
ARs and AEs, and AEs leading to discontinuation from IP or withdrawal from the study will be 
summarized. Unsolicited AEs will be presented by the Medical Dictionary for Regulatory Activities 
(MedDRA) preferred term and system organ class. 
The number of events of solicited ARs, unsolicited AEs/SAEs, and MAAEs will be reported in 
summary tables accordingly. 
Immunogenicity Analyses 
The SAP will describe the complete set of immunogenicity analyses, including the approach to sample 
participants into an Immunogenicity Subset for analysis of immunogenicity. The PP Immunogenicity 
Subset is the primary analysis set for immunogenicity unless otherwise specified. The primary 
immunogenicity objective of this study is to use the immunogenicity response to infer efficacy in 
adolescents (12 to < 18 years in this study). The primary immunogenicity analysis is performed in 
Part 1A. 
If an accepted serum Ab threshold of protection against COVID-19 is available based on data from 
other mRNA-1273 studies or external data, the number and percentage of participants with Ab greater 
than or equal to the threshold at Day 57 will be provided with a 2-sided 95% CI using the 
Clopper-Pearson method. If the lower bound of the 95% CI on the mRNA-1273 group is >70%, the 
primary immunogenicity objective of this study will be considered to be met. 
The percentage of participants with serum Ab greater than or equal to the threshold with 95% CI will 
be provided at each postbaseline timepoint. The CI will be calculated using the Clopper-Pearson 
method. 
If an accepted serum Ab threshold of protection against COVID-19 is not established, the 
noninferiority of primary vaccine response as measured by Ab GM value and seroresponse rate in 
adolescents compared with those in young adults (18 to 25 years of age) receiving mRNA-1273 will be 
assessed. The study is considered as meeting the primary immunogenicity objective if the 
noninferiority of the immune response to mRNA-1273 as measured by both GM value and 
seroresponse rate at Day 57 is demonstrated in adolescents in this study at a 2-sided α of 0.05, 
compared with that in young adults (18 to 25 years of age) in Study P301 receiving mRNA-1273. 
An analysis of covariance model will be carried out with Ab value at Day 57 as a dependent variable 
and a group variable (adolescents in Study P203 and young adults [18 to 25 years of age] in Study 
P301) as the fixed variable. The GM values of the adolescents at Day 57 will be estimated by the 
geometric least squares mean (GLSM) from the model. The GMR will be estimated by the ratio of 
GLSM from the model. A corresponding 2-sided 95% CI will be provided to assess the difference in 

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immune response for the adolescents in Study P203 compared to the young adults (18 to 25 years of 
age) in Study P301 at Day 57. The noninferiority of immune response to mRNA-1273 as measured by 
GM value will be considered demonstrated if the lower bound of the 95% CI of the GMR is >0.667 
based on the noninferiority margin of 1.5. 
The number and percentage (rate) of participants achieving Ab seroresponse at Day 57 will be 
summarized. The difference of seroresponse rates between adolescents receiving mRNA-1273 in Study 
P203 and young adults (18 to 25 years of age) receiving mRNA-1273 in Study P301 will be calculated 
with 95% CI. The noninferiority in seroresponse rate of adolescents in Study P203 compared to young 
adults (18 to 25 years of age) in Study P301 will be considered demonstrated if the lower bound of the 
95% CI of the seroresponse rate (SRR) difference is >-10%, based on the noninferiority margin of 
10%. 
In addition, the GM level of specific nAb and bAb with corresponding 95% CI will be provided at each 
timepoint. The 95% CIs will be calculated based on the t-distribution of the log transformed values 
then back transformed to the original scale. The GM fold‑rise of nAb and bAb with corresponding 95% 
CI will be provided at each timepoint with Day 57 as the primary timepoint of interest. Descriptive 
summary statistics including median, minimum, and maximum will also be provided. 
Efficacy Analyses 
To evaluate the incidence of COVID-19 after vaccination with mRNA-1273 or placebo, the incidence 
rate will be provided by vaccination group, calculated as the number of cases divided by the total 
person-time. The incidence rate ratio of mRNA-1273 versus placebo will be provided with 95% CI 
computed using the exact method conditional upon the total number of cases adjusted by the total 
person-time. 
For SARS-CoV-2 infection (serologically confirmed SARS-CoV-2 infection or COVID-19), regardless 
of symptomatology or severity, infection rate will be provided by vaccination group. The infection rate 
ratio of mRNA-1273 versus placebo may be provided with its 95% CI using the exact method 
conditional upon the total number of cases adjusted by the total person-time. The incidence rate of 
asymptomatic SARS-CoV-2 infection will also be provided. 
The secondary efficacy analyses will be performed in the PP set, with sensitivity analyses in the full 
analysis set (FAS), modified intent-to-treat (mITT) Set, and mITT1 Set. 
Long-Term Analysis (including Part 1B) 
Long-term analysis will be performed including data collected in the Open-label Observational Phase 
(Part 1B), and prior to BD if a BD is received. The analysis will include participants who are 
randomized to mRNA-1273 in Part 1A and remained in the study with or without unblinding, and 
participants who are originally randomized to placebo and later crossed over to receive mRNA-1273 in 
Part 1B after unblinding. Long-term analysis of applicable safety, efficacy, and immunogenicity 
endpoints will be summarized descriptively by treatment cohort without treatment group comparison. 
In the long-term safety analysis, unsolicited AEs will be summarized. 
In the long-term immunogenicity analysis, nAb and bAb values will be summarized at specified 
timepoints. 
In the long-term efficacy analysis, the incidence rates of COVID-19 and of SARS-CoV-2 infection 
cases will be counted starting 14 days after the second dose of IP for participants in treatment cohorts 

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of mRNA-1273 and Placebo or starting 14 days after the second dose of mRNA-1273 for participants 
in the Placebo-mRNA-1273 cohort. Incidence rate with 95% CI adjusting for person-time will be 
provided. The incidence rate of asymptomatic SARS-CoV-2 infection will also be provided. 
Hypothesis Testing (Part 1C-1 – Homologous Booster Phase) 
The immunogenicity analysis of BD vaccine response against the ancestral strain will be performed 
using the noninferiority tests of the 2 null hypotheses based on the 2 coprimary endpoints, respectively. 
Coprimary Endpoint 1: Ab GM value at BD-Day 29 
Null hypothesis 
H10: immunogenicity response to mRNA-1273 BD as measured by Ab GM value at BD-Day 29 in 
adolescents (12-<18 years of age) in Study P203 Part 1C-1 is inferior compared with Ab GM value at 
Day 57 (28 days after Dose 2) in the primary series of mRNA-1273 in young adults (18 to 25 years of 
age) in Study P301. 
The noninferiority in Ab GM at BD-Day 29 in Study P203 Part 1C-1 compared with Ab GM at Day 57 
in the primary series in young adults (18 to 25 years of age) in Study P301 will be demonstrated by the 
GMR 95% CI lower bound >0.667 using a noninferiority margin of 1.5. The GMR is defined as the 
GM value of Ab at BD-D29 in Study P203 Part 1C-1 compared with Ab GM value at Day 57 (28 days 
after Dose 2) following the primary series of mRNA-1273 in Study P301. 
Coprimary Endpoint 2: Ab Seroresponse Rate (SRR) at BD-Day 29 
Null hypothesis 
H20: immunogenicity response to mRNA-1273 BD as measured by SRR at BD-Day 29 in adolescents 
(12-<18 years of age) in Study P203 Part 1C-1 is inferior compared with SRR at Day 57 (28 days after 
Dose 2) following the primary series of mRNA-1273 in young adults (18 to 25 years of age) in 
Study P301. 
The noninferiority in SRR at BD-D29 compared with SRR at Day 57 (28 days after Dose 2) following 
the primary series of mRNA-1273 will be demonstrated by the SRR 95% CI lower bound >-10% using 
the noninferiority margin of 10%. The SRR difference is defined as the SRR at BD-Day 29 Study P203 
Part 1C-1 minus the rate at Day 57 (28 days after Dose 2) following the primary series of mRNA-1273 
in young adults in Study P301. Seroresponse is defined as Ab value change from baseline (pre Dose 1) 
below the lower limit of quantification (LLOQ) to ≥4 × LLOQ, or at least a 4-fold rise if baseline is 
≥ LLOQ. 
The primary immunogenicity objective in Part 1C-1 is met if the noninferiority is demonstrated based 
on both coprimary endpoints. 
Key Secondary Endpoint 1: GM value of Ab Against Circulating Strain at BD-Day 29 
Null hypothesis 
H10: immunogenicity response to mRNA-1273 BD as measured by GM value of Ab against circulating 
strain at BD-Day 29 in adolescents (12-<18 years of age) in Study P203 Part 1C-1 is inferior compared 
with GM value of Ab against circulating strain at Day 57 (28 days after Dose 2) in the primary series of 
mRNA-1273 in young adults (18 to 25 years of age) in Study P301. 

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The noninferiority in Ab GM value at BD-Day 29 in Study P203 Part 1C-1 compared with Ab GM 
value at Day 57 in the primary series in young adults (18 to 25 years of age) in Study P301 will be 
demonstrated by the GMR 95% CI lower bound >0.667 using a noninferiority margin of 1.5. The GMR 
is defined as the ratio of GM value of Ab at BD-Day 29 in Study P203 Part 1C-1 compared with Ab 
GM value at Day 57 (28 days after Dose 2) following the primary series of mRNA-1273 in 
Study P301. 
Key Secondary Endpoint 2: Seroresponse Rate (SRR) of Ab Against Circulating Strain at BD-Day 29 
Null hypothesis 
H20: immunogenicity response to mRNA-1273 BD as measured by SRR of Ab against circulating 
strain at BD-Day 29 in adolescents (12-<18 years of age) in Study P203 Part 1C-1 is inferior compared 
with SRR of Ab against circulating strain at Day 57 (28 days after Dose 2) following the primary series 
of mRNA-1273 in young adults (18 to 25 years of age) in Study P301. 
The noninferiority in SRR at BD-D29 compared with SRR at Day 57 (28 days after Dose 2) following 
the primary series of mRNA-1273 will be demonstrated by the SRR 95% CI lower bound >-10% using 
the noninferiority margin of 10%. The SRR difference is defined as the SRR at BD-Day 29 Study P203 
Part 1C-1 minus the rate at Day 57 (28 days after Dose 2) following the primary series of mRNA-1273 
in young adults in Study P301. Seroresponse is defined as Ab value change from baseline (pre Dose 1) 
below the LLOQ to ≥4 × LLOQ, or at least a 4-fold rise if baseline is ≥ LLOQ. 
The key secondary immunogenicity objective in Part 1C-1 is met if the noninferiority is demonstrated 
based on both key secondary endpoints. 
Power and Sample Size (Part 1C-1 – Homologous Booster Phase) 
All participants enrolled in Part 1A or Part 1B who meet the eligibility criteria for BD will be offered a 
BD of mRNA-1273 50 µg. With more than 1,000 participants expected to receive mRNA‑1273 BD, 
the study Part 1C-1 has a 90% probability to observe at least 1 participant with an AE at a true AE rate 
of 0.25%. 
Serum samples from all participants will be collected and banked, a subset of participants will be 
selected, and their samples will be processed for immunogenicity testing (the Immunogenicity Subset) 
at specified timepoints. 
Approximately 400 participants who receive mRNA-1273 BD will be selected for the Immunogenicity 
Subset for Part 1C-1, with a target of 289 participants receiving mRNA-1273 BD in the PP 
Immunogenicity Subset with prebooster negative SARS-CoV-2 for Part 1C-1 (adjusting for 
approximately 25% of participants who may be excluded as they may have prebooster positive 
SARS-CoV-2, have no immunogenicity results due to any reason or have protocol deviations 
impacting critical data). 
For the primary immunogenicity objective in Part 1C-1, noninferiority tests of 2 null hypotheses based 
on 2 coprimary endpoints, respectively, will be performed. 
• 
With approximately 289 participants receiving mRNA-1273 BD in the PP Immunogenicity 
Subset with prebooster negative SARS-CoV-2 in Study P203 Part 1C-1 and 289 
participants in the PP Immunogenicity Subset in young adults (18 to 25 years of age) in 
Study P301, there will be 90% power to demonstrate noninferiority of the immune 
response post BD as measured by Ab GM value in adolescents in Study P203 Part 1C-1 

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compared with Ab GM value in young adults (18 to 25 years of age) following primary 
series of mRNA-1273 in Study P301, at a 2-sided α of 0.05, assuming an underlying GMR 
value of 1 and a noninferiority margin of 1.5. The SD of the log‑transformed levels is 
assumed to be 1.5. 
• 
With approximately 289 participants receiving mRNA-1273 BD in the PP Immunogenicity 
Subset with prebooster negative SARS-CoV-2 in Study P203 Part 1C-1 and 
289 participants in the PP Immunogenicity Subset in young adults (18 to  
25 years of age) in Study P301, there will be at least 90% power to demonstrate 
noninferiority of the immune response post BD as measured by SRR in adolescents in 
Study P203 Part 1C-1 compared with SRR in young adults of (18 to 25 years of age) 
following primary series of mRNA-1273 in Study P301, at a 2-sided α of 0.05, assuming 
true SRR of 90% in young adults (18 to 25 years of age) following primary series of 
mRNA-1273 in Study P301, and a true SRR of 90% post BD in adolescents in Study P203 
Part 1C-1 (ie, true rate difference is 0 compared to young adults [18 to 25 years of age] 
from Study P301), and a noninferiority margin of 10%. 
Homologous Booster Phase Analysis (Part 1C-1) 
Booster Phase analysis will be performed in participants who receive a BD in Part 1C-1. Safety, 
immunogenicity endpoints, and incidence of COVID-19 and SARS-CoV-2 infection will be 
summarized descriptively, and by prebooster SARS-CoV-2 status if applicable. 
In the Booster Phase safety analysis, the number and percentage of participants with unsolicited AEs, 
severe AEs, treatment-related AEs, SAEs, MAAEs, AESIs, and AEs leading to discontinuation from 
the study participation in Part 1C-1 will be summarized. 
The number and percentage of participants with any solicited local AR, with any solicited systemic 
AR, and with any solicited AR during the 7-day follow-up period after the BD will be provided. 
In the Part 1C-1 Booster Phase, for the coprimary endpoints (Ab GM value and SRR against the 
ancestral strain) and key secondary endpoints (Ab GM value and SRR against the circulating strain), 
the following analyses will be performed for the respective hypothesis testing: 
• 
The GM titers with 95% CI will be summarized using t-distribution of the log transferred 
values and then back transformed to the original scale. The GMR with 95% CI to compare 
postbooster GM value at BD-Day 29 in adolescents in Study P203 with the primary series 
GM value at Day 57 (28 days after Dose 2) in young adults (18 to 25 years of age) in 
Study P301 will be computed based on the t-distribution of mean difference in the log 
transferred values and then back transformed to the original scale. 
• 
The SRR with 95% CI (using Clopper-Pearson method) will be summarized. The SRR 
difference with 95% CI (using Miettinen-Nurminen score method) to compare postbooster 
SRR at BD-Day 29 in adolescents in Study P203 with the primary series SRR at Day 57 
(28 days after Dose 2) in young adults in Study P301 will be computed. Seroresponse is 
defined as Ab value change from baseline (pre Dose 1) below the LLOQ to ≥4 × LLOQ, or 
at least a 4-fold rise if baseline is ≥ LLOQ. 
In the Booster Phase immunogenicity analyses, the GM titers or levels for specific nAb and bAb, with 
corresponding 95% CI will be provided at BD-Day 1, BD-Day 29, BD-Day 181, and BD-Day 361 
(Part 1C-1). Geometric mean fold rise (GMFR) relative to pre Dose 1, BD-Day 1 and prior Day 57 in 

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the phase of primary 2-dose series of mRNA-1273 will be summarized with 95% CIs at BD-Day 29, 
BD-Day 181, and BD-Day 361 (Part 1C-1). The 95% CIs will be calculated based on the t-distribution 
of the log transformed values then back transformed to the original scale. Descriptive summary 
statistics including median, minimum, and maximum will also be provided. The immunogenicity 
descriptive summaries will be provided in the participants who have available nAb and bAb assay 
results for the specified timepoints. 
In the Booster Phase, the incidence rate of the first occurrence of symptomatic COVID-19 starting 
14 days after the BD will be summarized by prebooster SARS-CoV-2 status. The incidence rate of 
SARS-CoV-2 infection (symptomatic or asymptomatic infection) starting 14 days after the BD, and the 
incidence rate of asymptomatic SARS-CoV-2 infection starting 14 days after the BD will be 
summarized. The incidence rates with 95% CI will be computed adjusting for person-years starting 
from BD-Day 1 in Part 1C-1. 
Part 1C-2 Heterologous Booster Phase 
Power and Sample Size 
Approximately 362 participants who received non-Moderna COVID-19 vaccine as primary series 
vaccination at least 3 months prior were planned to be enrolled to receive mRNA-1273 50 µg as 
heterologous booster in Part 1C-2. However, the study population in Part 1C-2 will have less than the 
planned number of participants enrolled, as a result of slow enrollment and discontinuation of 
recruitment in Part 1C-2. 
Heterologous Booster Phase Analysis (Part 1C-2) 
Heterologous Booster Phase analysis will be performed in participants who receive mRNA-1273 50 µg 
in Part 1C-2. Safety, immunogenicity endpoints, and incidence of COVID-19 and SARS-CoV-2 
infection will be summarized descriptively, and by prebooster SARS-CoV-2 status if applicable. 
In the Heterologous Booster Phase safety analysis, the number and percentage of participants with 
unsolicited AEs, severe AEs, treatment-related AEs, SAEs, MAAEs, AESIs, and AEs leading to 
discontinuation from the study participation in Part 1-C2 will be summarized. 
The number and percentage of participants with any solicited local AR, with any solicited systemic 
AR, and with any solicited AR during the 7-day follow-up period after the BD will be provided. 
In the Heterologous Booster Phase immunogenicity analyses, the GM titers or levels for specific nAb 
and bAb (against the ancestral strain or against specific circulating variants of interest), with 
corresponding 95% CI will be provided at BD-Day 1, BD-Day 29, BD-Day 181, and BD-Day 361. 
GMFR relative to BD-Day 1 will be summarized with 95% CIs at BD-Day 29, and BD-Day 181, and 
BD-Day 361. The 95% CIs will be calculated based on the t-distribution of the log transformed values 
then back transformed to the original scale. Descriptive summary statistics including median, 
minimum, and maximum will also be provided for GM value and GMFR. The SRR and category of at 
least 2-fold rise relative to BD-Day 1 will be summarized with numbers and percentages of 
participants. The immunogenicity descriptive summaries will be provided in the PP Immunogenicity 
Subset who have available nAb and bAb assay results for the specified timepoints. 
In the Heterologous Booster Phase, the incidence rate of the first occurrence of symptomatic 
COVID-19 starting 14 days after the BD will be summarized by prebooster SARS-CoV-2 status. The 
incidence rate of SARS-CoV-2 infection (symptomatic or asymptomatic infection) starting 14 days 

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after the BD, and the incidence rate of asymptomatic SARS-CoV-2 infection starting 14 days after the 
BD will be summarized. The incidence rates with 95% CI will be computed adjusting for person-years 
starting from BD-Day 1 in Part 1C-2. 
Part 2 
There will be no hypothesis testing in Part 2, given that the enrollment in Part 2 was discontinued. All 
analyses for Part 2 will be descriptive based on available data. 
Part 2 Power and Sample Size 
Approximately 362 participants were planned to be enrolled to receive mRNA-1273 50 µg in the 
open-label Part 2. However, the study population in Part 2 will have less than the planned number of 
participants receiving at least one dose of 50 µg mRNA-1273, with a small sample size as a result of 
slow enrollment and discontinuation of recruitment in Part 2. 
Part 2 Analyses 
Part 2 safety and immunogenicity endpoints will be summarized descriptively. 
In the safety analysis, the number and percentage of participants with unsolicited AEs, severe AEs, 
treatment-related AEs, SAEs, MAAEs, AESIs, and AEs leading to discontinuation from the study 
participation in Part 2 will be summarized. 
The number and percentage of participants with any solicited local AR, with any solicited systemic 
AR, and with any solicited AR during the 7-day follow-up period after each injection will be provided. 
In the immunogenicity descriptive analyses, the GM value for specific Ab (against the ancestral strain 
or against specific circulating variants of concern) with corresponding 95% CI, and GMFR from 
baseline with 95% CI will be provided by timepoint. GM and GMFR 95% CIs will be calculated based 
on the t-distribution of the log transformed values then back transformed to the original scale. 
Descriptive summary statistics including median, minimum, and maximum will also be provided for 
GM and GMFR. The SRR and category of at least 2-fold rise from baseline by timepoint will be 
summarized with numbers and percentages of participants. The immunogenicity descriptive summaries 
will be provided in the PP Immunogenicity Subset who have available nAb and bAb assay results for 
the specified timepoints. 
Part 3 
Hypothesis testing for the endpoints that infer effectiveness of the 50 µg mRNA-1273.222 in 
adolescents will be performed on the null hypotheses for the 2 coprimary endpoints as follows: 
Coprimary Endpoint 1: Post Dose 1 Ab GM value against Omicron BA.4/BA.5 at Day 29 
(superiority testing) 
The null hypothesis H0: GM value of Ab against Omicron BA.4/BA.5 at Day 29 post Dose 1 of 50 µg 
mRNA-1273.222 in adolescents who are baseline SARS-CoV-2 positive is not superior to GM value at 
Day 57 post Dose 2 of 100 µg mRNA-1273 in young adults (18 to 25 years of age baseline 
SARS-CoV-2 negative) in Study P301.  
The superiority in Ab GM value against Omicron BA.4/BA.5 in adolescents who are baseline 
SARS-CoV-2 positive compared with that in young adults (18 to 25 years of age baseline 
SARS-CoV-2 negative) is demonstrated by meeting the following success criterion: 

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• The lower bound of the 95% CI of the GMR >1. 
The GMR is the ratio of the GM value against Omicron BA.4/BA.5 at Day 29 post Dose 1 of 50 µg 
mRNA-1273.222 in adolescents who are baseline SARS-CoV-2 positive in Study P203 Part 3 over the 
GM value against Omicron BA.4/BA.5 at Day 57 in young adults (18 to 25 years of age baseline 
SARS-CoV-2 negative) post Dose 2 of 100 µg mRNA-1273 in Study P301. 
Coprimary Endpoint 2: Post Dose 1 Ab GM value against the ancestral strain at Day 29 
(noninferiority testing) 
The null hypothesis H0: GM value of Ab against the ancestral strain at Day 29 post Dose 1 of 50 µg 
mRNA-1273.222 in adolescents who are baseline SARS-CoV-2 positive is inferior to GM value at 
Day 57 post Dose 2 of 100 µg mRNA-1273 in young adults (18 to 25 years of age baseline 
SARS-CoV-2 negative) in Study P301. 
The noninferiority in Ab GM value against the ancestral strain in adolescents who are baseline 
SARS-CoV-2 positive compared with that in baseline SARS-CoV-2 negative young adults (18 to 
25 years of age) is demonstrated by meeting the following success criterion: 
• 
The lower bound of the 95% CI of the GMR >0.667. 
The GMR is the ratio of the GM value against the ancestral strain at Day 29 post Dose 1 of 50 µg 
mRNA-1273.222 in adolescents who are baseline SARS-CoV-2 positive in Study P203 Part 3 over the 
GM value against ancestral strain at Day 57 in baseline SARS-CoV-2 negative young adults (18 to 
25 years of age) post Dose 2 of 100 µg mRNA-1273 in Study P301. 
Part 3 Power and Sample Size 
With at least 300 adolescents enrolled in Part 3 to receive 50 µg mRNA-1273.222, the study will have 
at least a 95% probability to observe at least 1 participant with an AE at a true AE rate of 1%.  
Assuming a true serum Ab GMR of 1.6 for GM value against Omicron BA.4/BA.5 at Day 29 after 
Dose 1 of mRNA-1273.222 in baseline SARS-CoV-2 positive adolescents compared with GM value 
against Omicron BA.4/BA.5 at Day 57 after Dose 2 of mRNA-1273 primary series in young adults 
who are baseline SARS-CoV-2 negative in P301, with approximately 168 participants in the PP 
Immunogenicity Subset who are baseline SARS-CoV-2 positive in P203 Part 3 and 300 young adults 
in P301 who are baseline SARS-CoV-2 negative, there will be at least >90% power to demonstrate 
superiority of the serum Ab GM value against Omicron BA.4/BA.5 after Dose 1 of mRNA-1273.222 in 
adolescents in P203 to that after Dose 2 of mRNA-1273 in young adults in Study P301 at two-sided α 
of 0.05 using a superiority margin of 1.0. The standard deviation of the natural log transformed levels 
of Ab is assumed to be 1.5. 
Assuming a true serum Ab GMR of 1.1 for GM value against ancestral strain at Day 29 after Dose 1 of 
mRNA-1273.222 in baseline SARS-CoV-2 positive adolescents compared with GM value against 
ancestral strain at Day 57 after Dose 2 of mRNA-1273 primary series in young adults who are baseline 
SARS-CoV-2 negative in P301, this sample size will also provide at least >90% power to demonstrate 
noninferiority of GM value of Ab against ancestral strain at Day 29 post Dose 1 of mRNA-1273.222 in 
adolescents in P203 to that after Dose 2 of mRNA-1273 in young adults in Study P301 at two-sided α 

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of 0.05 using a noninferiority margin of 1.5. The standard deviation of the natural log transformed 
levels of Ab is assumed to be 1.5. 
With approximately 30% of participants in Part 3 who may be excluded from the PP Immunogenicity 
Subset-baseline SARS-CoV-2 positive (PPIS-POS), as they may be baseline SARS-CoV-2 negative or 
have missing immunogenicity results due to any reason or protocol deviations impacting critical data, 
approximately 240 participants are required in Part 3 to provide 168 participants in the PP 
Immunogenicity Subset-baseline SARS-CoV-2 positive. 
Part 3 Analyses 
In the safety analysis, the number and percentage of participants with unsolicited AEs, severe AEs, 
treatment-related AEs, SAEs, MAAEs, AESIs, and AEs leading to discontinuation from the study 
participation in Part 3 will be summarized. 
The number and percentage of participants with any solicited local AR, with any solicited systemic 
AR, and with any solicited AR during the 7-day follow-up period after each injection will be provided. 
In the Part 3 immunogenicity analysis, for the coprimary endpoints (Ab GM value against Omicron 
BA.4/BA.5 and the ancestral strain at Day 29 after Dose 1 of 50 µg mRNA-1273.222 in baseline 
SARS-CoV-2 positive adolescents in Study P203 compared with those at Day 57 after Dose 2 of 
100 µg mRNA-1273 in baseline SARS-CoV-2 negative adults 18 to 25 years of age in Study P301), 
the following analyses will be performed for the respective hypothesis testing: 
An ANCOVA model will be carried out with Ab value at Day 29 in P203 and Ab value at Day 57 in 
P301 as a dependent variable and a group variable (baseline SARS-CoV-2 positive adolescents in 
Study P203 and baseline negative SARS-CoV-2 young adults in Study P301) as the fixed variable, 
where a covariate may be included in the model (to be specified in the SAP). The GM value at Day 29 
in P203 and the GM value at Day 57 in P301, and respective GMR for P203 compared to P301 will be 
estimated from the model. A corresponding 2-sided 95% CI of GMR estimated from the ANCOVA 
model will be provided to assess the difference in immune response after Dose 1 (Day 29) for the 
adolescents in Study P203 compared to that after Dose 2 (Day 57) in the young adults (18 to 25 years 
of age) in Study P301. 
The first coprimary endpoint, superiority of immune response to mRNA-1273.222 against Omicron 
BA.4/BA.5 after Dose 1 compared to mRNA-1273 against Omicron BA.4/BA.5 after Dose 2 as 
measured by GM value will be considered demonstrated if the respective GMR 95% CI lower bound is 
>1 based on a superiority margin of 1. 
The second coprimary endpoint, noninferiority of immune response to mRNA-1273.222 against 
ancestral strain after Dose 1 compared to mRNA-1273 against the ancestral strain after Dose 2 as 
measured by GM value will be considered demonstrated if the respective GMR 95% CI lower bound is 
>0.667 based on the noninferiority margin of 1.5. The GM value and GMR with specified CIs will also 
be summarized using t-distribution of the log transferred values and then back transformed to the 
original scale, and by baseline SARS-CoV-2 status. 
Secondary endpoints evaluating SRR with 95% CIs (using Clopper-Pearson method) will be 
summarized by baseline SARS-CoV-2 status at Day 29 in adolescents in Study P203, and at Day 57 in 
young adults in Study P301. Seroresponse at subject level is defined as Ab value change from baseline 
(preDose 1) below the LLOQ to ≥4 × LLOQ, or at least a 4-fold rise if baseline is ≥LLOQ. The SRR 

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and category of at least 2-fold rise from baseline by timepoint will be summarized with numbers and 
percentages of participants. 
The GM values for specific nAb and bAb, with corresponding 95% CIs, and GMFR from baseline with 
95% CIs will be summarized by timepoint. The 95% CIs will be calculated based on the t-distribution 
of the log transformed values then back transformed to the original scale. Descriptive summary 
statistics including median, minimum, and maximum will also be provided.  
The incidence rate of the first occurrence of symptomatic COVID-19, 14 days after Dose 1 will be 
summarized. The incidence rates with 95% CIs will be computed adjusting for person-years. 
Analysis Sets 
The analysis sets are defined in the following table: 
Analysis Set 
Description 
Randomization Set 
All participants who are randomized, regardless of the 
participants’ treatment status in the study. 
FAS 
All randomized participants who received at least 1 injection of 
IP. 
Immunogenicity Subset 
A subset of participants in the FAS will be selected for 
immunogenicity testing. 
PP Immunogenicity Subset  
A subset of participants in the FAS will be selected for 
immunogenicity testing. The PP Immunogenicity Subset includes 
participants selected for the Immunogenicity Subset who received 
planned doses of study vaccination per schedule, complied with 
immunogenicity testing schedule, and have no major protocol 
deviations that impact key or critical data. Participants who are 
seropositive at baseline will be excluded from the PP 
Immunogenicity Subset. The PP Immunogenicity Subset will be 
used for analyses of immunogenicity unless specified otherwise. 
PP Set for Efficacy 
All participants in the FAS who received planned doses of study 
vaccination, had no immunologic or virologic evidence of prior 
COVID-19, and have no major protocol deviations that impact 
key or critical efficacy data. 
Safety Set 
All randomized participants who receive at least 1 dose of IP. The 
Safety Set will be used for all analyses of safety except for the 
solicited ARs. 
mITT1 Set 
All participants in the mITT Set excluding those who received the 
wrong treatment (ie, at least 1 dose received is not as randomized 
or planned). 
PP Immunogenicity Subset for 
BD phase 
The PP Immunogenicity Subset for BD phase includes 
participants who received planned BD per schedule, complied 
with immunogenicity testing schedule, and have no major 
protocol deviations that impact key or critical data, with 
prebooster negative or positive SARS-CoV-2. The PP 

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Immunogenicity Subset with prebooster negative SARS-CoV-2 
will be used for the primary immunogenicity analysis. 
PP Immunogenicity Subset for 
Part 3 
The PP Immunogenicity Subset for Part 3 includes participants 
who received planned dose per schedule, complied with 
immunogenicity testing schedule, and have no major protocol 
deviations that impact key or critical data, with baseline negative 
or positive SARS-CoV-2. The PP Immunogenicity Subset for 
Part 3 with baseline-positive SARS-CoV-2 status will serve as the 
population for the primary and secondary analysis of 
immunogenicity data at Day 29 in Part 3.  
Abbreviations: AR = adverse reaction; bAb = binding antibody; COVID-19 = coronavirus disease 
2019; FAS = full analysis set; IP = investigational product; mITT = modified intent-to-treat; 
PP = per-protocol; RT-PCR = reverse transcription polymerase chain reaction; 
SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2.  
Note: Positive SARS-CoV-2 status at baseline is defined as a positive RT-PCR test for SARS-CoV-2, 
and/or a positive serology test based on bAb specific to SARS-CoV-2 nucleocapsid (as measured by 
Roche Elecsys Anti-SARS-CoV-2 assay) on or before Day 1. Negative status is defined as a negative 
RT-PCR test for SARS-CoV-2, and a negative serology test based on bAb specific to SARS-CoV-2 
nucleocapsid (as measured by Roche Elecsys Anti-SARS-CoV-2 assay) on or before Day 1. 
Multiplicity Adjustment 
A hierarchical sequential hypothesis testing (fixed-sequence) method will be used to adjust multiplicity 
to preserve the family-wise type I error rate (α = 0.05). The hypothesis testing for the 2 coprimary 
endpoints (geometric mean titer [GMT] and SRR) for the primary series of mRNA-1273 in Part 1A 
was completed and statistically significant based on data snapshot dated 08 May 2021, and thus the α 
level of 0.05 can be passed to Part 1C-1 hypothesis testing. In Part 1C-1 Homologous Booster Phase, 
the hypothesis testing for the 2 coprimary endpoints (GMT and SRR against the ancestral strain) after 
BD of mRNA-1273 will be tested at α level of 0.05. The testing in Part 1A and 1C-1 will continue 
through the sequence only until an endpoint is not statistically significant (did not meet specified 
noninferiority success criteria), in which case the testing will stop. If the hypothesis testing for the 2 
coprimary endpoints in Part 1C-1-Homologous Booster Phase is statistically significant (meeting the 
noninferiority success criteria of the coprimary endpoints), the α level of 0.05 will be passed to the 
hypothesis testing in Part 3. 
For the key secondary objective in Part 1C-1 Homologous Booster Phase to evaluate immune response 
elicited by the 50 µg prototype booster of mRNA-1273 against variant(s) of interest, the key secondary 
endpoints will be analyzed independently, given that prototype vaccine mRNA-1273 does not contain 
variant specific sequences. 
Part 3 
Since the hypothesis testing for the coprimary endpoints in Part 1C-1 was statistically significant based 
on an interim analysis (IA) with a data cutoff dated 16 May 2022, the α level of 0.05 (two-sided) was 
passed to Part 3 hypothesis testing. 
Study Analyses: 
Interim Analyses 
More than one IA may be performed. 

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• 
The IA of immunogenicity, safety, and efficacy will be performed after Day 57 
immunogenicity data are available for the Immunogenicity Subset and at least 
1,500 participants (1,000 participants receiving mRNA-1273) have completed Day 57 
(1 month after Dose 2, Part 1A). This IA will be considered the primary analysis of 
immunogenicity for Part 1A. 
• 
An IA of immunogenicity and safety may be performed after all or subset of participants who 
receive BD have completed BD-Day 29 after the BD in Part 1C-1. 
• 
An IA of immunogenicity and safety may be performed after all or subset of participants who 
receive heterologous BD have completed BD-Day 29 after the BD in Part 1C-2. 
• 
An IA of immunogenicity and safety may be performed after Day 57 immunogenicity data are 
available after all or a subset of participants in Part 2 have completed Day 57 (1 month after 
Dose 2, Part 2). 
• 
An IA of immunogenicity and safety may be performed after all or a subset of participants who 
receive 50 µg mRNA-1273.222 dose have completed Day 29 (1 month after Dose 1). 
• 
At the Sponsor’s discretion, a clinical study report (CSR) may be developed for an IA. 
Final Analysis 
The final analysis of all applicable endpoints will be performed after all participants have completed all 
planned study procedures. Results of this analysis will be presented in a final CSR, including 
individual listings. 

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TABLE OF CONTENTS 
CLINICAL STUDY PROTOCOL ..................................................................................................1 
PROTOCOL APPROVAL – SPONSOR SIGNATORIES .............................................................2 
DECLARATION OF INVESTIGATOR .........................................................................................3 
PROTOCOL AMENDMENT SUMMARY OF CHANGES ..........................................................4 
PROTOCOL SYNOPSIS ................................................................................................................8 
TABLE OF CONTENTS ...............................................................................................................44 
LIST OF TABLES .........................................................................................................................49 
LIST OF FIGURES .......................................................................................................................49 
LIST OF ABBREVIATIONS AND TERMS ................................................................................51 
1. 
INTRODUCTION ......................................................................................................54 
1.1. 
Study Rationale ...........................................................................................................54 
1.2. 
Background and Overview .........................................................................................57 
1.2.1. 
Nonclinical Studies .....................................................................................................58 
1.2.2. 
Clinical Studies ...........................................................................................................59 
1.3. 
Benefit/Risk Assessment ............................................................................................68 
1.3.1. 
Potential Benefits from Participation ..........................................................................68 
1.3.2. 
Risks to Study Participants and Risk Mitigation ........................................................68 
1.3.3. 
Overall Benefit/Risk Conclusion ................................................................................70 
2. 
OBJECTIVES AND ENDPOINTS ............................................................................71 
3. 
STUDY DESIGN .......................................................................................................80 
3.1. 
General Design ...........................................................................................................80 
3.1.1. 
Part 1 Study Design ....................................................................................................80 
3.1.2. 
Part 2 Study Design ....................................................................................................87 
3.1.3. 
Part 3 Study Design ....................................................................................................89 
3.2. 
Scientific Rationale for Study Design ........................................................................91 
3.3. 
Justification for Dose, Control Product, and Choice of Study Population .................93 
3.4. 
End-of-Study Definition .............................................................................................95 
4. 
STUDY POPULATION .............................................................................................96 
4.1. 
Eligibility Criteria (Part 1A, Part 2, and Part 3) .........................................................96 
4.1.1. 
Inclusion Criteria ........................................................................................................96 
4.1.2. 
Exclusion Criteria .......................................................................................................96 

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4.2. 
Study Eligibility Criteria (Part 1B) .............................................................................98 
4.3. 
Study Eligibility Criteria (Part 1C-1 – Homologous Booster Phase) .........................98 
4.4. 
Study Eligibility Criteria (Part 1C-2 – Heterologous Booster Dose): ........................99 
4.5. 
Lifestyle Restrictions ................................................................................................100 
4.6. 
Screen Failures (Part 1A: Blinded Phase, Part 2, and Part 3) ...................................101 
5. 
STUDY TREATMENT ............................................................................................102 
5.1. 
Investigational Product Administered ......................................................................102 
5.2. 
Randomization (Part 1A Only) .................................................................................102 
5.3. 
Dosing and Management of mRNA-1273 Vaccine ..................................................102 
5.3.1. 
Preparation of Study Vaccine for Injection ..............................................................102 
5.3.2. 
Administration of Study Vaccine .............................................................................103 
5.3.3. 
Study Vaccine Delivery and Receipt ........................................................................103 
5.3.4. 
Study Vaccine Packaging and Labeling ...................................................................104 
5.3.5. 
Study Vaccine Storage ..............................................................................................104 
5.3.6. 
Study Vaccine Accountability ..................................................................................104 
5.3.7. 
Study Vaccine Handling and Disposal .....................................................................105 
5.4. 
Study Treatment Compliance ...................................................................................105 
5.5. 
Prior and Concomitant Medications .........................................................................105 
5.5.1. 
Prior Medications and Therapies ..............................................................................105 
5.5.2. 
Concomitant Medications and Therapies .................................................................105 
5.5.3. 
Recording of Concomitant Medications and Concomitant Vaccinations ..................106 
5.5.4. 
Concomitant Medications and Vaccines that May Lead to the Elimination of 
a Participant from Per-Protocol Analyses ..................................................................107 
5.6. 
Intervention After the End of the Study ...................................................................107 
6. 
DELAYING OR DISCONTINUING STUDY TREATMENT AND 
PARTICIPANT WITHDRAWAL FROM THE STUDY ........................................108 
6.1. 
Criteria for Delay of Vaccine Administration ..........................................................108 
6.1.1. 
Individual Participant Criteria for Delay of Study Vaccination ...............................108 
6.2. 
Discontinuing Study Vaccination .............................................................................108 
6.3. 
Participant Discontinuation/Withdrawal from the Study .........................................109 
6.4. 
Study Pause Rules.....................................................................................................110 
6.5. 
Lost to Follow-up .....................................................................................................111 
7. 
STUDY ASSESSMENTS AND PROCEDURES ....................................................112 

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7.1. 
Safety Assessments and Procedures .........................................................................113 
7.1.1. 
Use of Electronic Diaries ..........................................................................................113 
7.1.2. 
Safety Telephone Calls .............................................................................................116 
7.1.3. 
Safety Laboratory Assessments ................................................................................116 
7.1.4. 
Vital Sign Measurements ..........................................................................................116 
7.1.5. 
Physical Examinations ..............................................................................................117 
7.1.6. 
Assessment for SARS-CoV-2 Infection ...................................................................117 
7.2. 
Immunogenicity Assessments ..................................................................................118 
7.3. 
Exploratory Assessments and Biomarkers ...............................................................119 
7.4. 
Efficacy Assessments ...............................................................................................119 
7.4.1. 
Vaccine Effectiveness Assessments .........................................................................119 
7.4.2. 
Surveillance for COVID-19 Symptoms ....................................................................120 
7.4.3. 
Follow-up/Convalescent Period After Diagnosis with COVID-19 ..........................123 
7.5. 
Safety Definitions and Related Procedures ..............................................................123 
7.5.1. 
Adverse Event ...........................................................................................................123 
7.5.2. 
Serious Adverse Events ............................................................................................124 
7.5.3. 
Solicited Adverse Reactions .....................................................................................125 
7.5.4. 
Medically Attended Adverse Events ........................................................................127 
7.5.5. 
Adverse Events of Special Interest ...........................................................................128 
7.5.6. 
Recording and Follow-up of Pregnancy ...................................................................131 
7.5.7. 
Eliciting and Documenting Adverse Events .............................................................131 
7.5.8. 
Assessment of Intensity ............................................................................................132 
7.5.9. 
Assessment of Causality ...........................................................................................133 
7.5.10. 
Reporting Adverse Events ........................................................................................133 
7.5.11. 
Reporting SAEs ........................................................................................................133 
7.5.12. 
Time Period and Frequency for Collecting AE and SAE Information .....................134 
7.5.13. 
Method of Detecting AEs and SAEs ........................................................................134 
7.5.14. 
Follow-up of AEs and SAEs .....................................................................................135 
7.5.15. 
Regulatory Reporting Requirements for SAEs .........................................................135 
7.6. 
Safety Monitoring .....................................................................................................135 
7.6.1. 
Data Safety Monitoring Board ..................................................................................135 
7.6.2. 
Independent Cardiac Event Adjudication Committee ..............................................136 
7.7. 
Treatment of Overdose .............................................................................................136 

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7.8. 
Pharmacokinetics ......................................................................................................136 
7.9. 
Pharmacodynamics ...................................................................................................136 
7.10. 
Biomarkers ................................................................................................................136 
7.11. 
Health Economics .....................................................................................................136 
8. 
STATISTICAL ANALYSIS PLAN .........................................................................137 
8.1. 
Blinding and Responsibility for Analyses ................................................................137 
8.1.1. 
Breaking the Blind ....................................................................................................138 
8.2. 
Statistical Hypothesis ................................................................................................138 
8.2.1. 
Part 1 .........................................................................................................................138 
8.2.2. 
Part 2 .........................................................................................................................140 
8.2.3. 
Part 3 .........................................................................................................................141 
8.3. 
Power and Sample Size ............................................................................................141 
8.3.1. 
Part 1 .........................................................................................................................141 
8.3.2. 
Part 2 .........................................................................................................................144 
8.3.3. 
Part 3 .........................................................................................................................144 
8.4. 
Analysis Sets .............................................................................................................144 
8.5. 
Statistical Methods ....................................................................................................146 
8.5.1. 
Baseline Characteristics and Demographics .............................................................146 
8.5.2. 
Safety Analyses ........................................................................................................146 
8.5.3. 
Immunogenicity Analyses in Part 1 ..........................................................................147 
8.5.4. 
Efficacy Analyses .....................................................................................................148 
8.5.5. 
Long-term Analysis (Including Part 1B) ..................................................................148 
8.5.6. 
Booster Phase Analysis .............................................................................................149 
8.5.7. 
Part 2 Analysis ..........................................................................................................150 
8.5.8. 
Part 3 Analysis ..........................................................................................................151 
8.5.9. 
Exploratory Analyses ................................................................................................152 
8.5.10. 
Subgroup Analyses ...................................................................................................152 
8.6. 
Multiplicity Adjustment............................................................................................152 
8.7. 
Study Analyses .........................................................................................................153 
8.7.1. 
Interim Analyses .......................................................................................................153 
8.7.2. 
Final Analysis ...........................................................................................................153 
9. 
REFERENCES .........................................................................................................154 

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10. 
SUPPORTING DOCUMENTATION AND OPERATIONAL 
CONSIDERATIONS ................................................................................................160 
10.1. 
APPENDIX 1: Schedule of Assessments .................................................................161 
10.2. 
APPENDIX 2: Study Governance Considerations ...................................................194 
10.2.1. 
Regulatory and Ethical Considerations ....................................................................194 
10.2.2. 
Study Monitoring ......................................................................................................194 
10.2.3. 
Audits and Inspections ..............................................................................................195 
10.2.4. 
Financial Disclosure .................................................................................................196 
10.2.5. 
Recruitment Procedures ............................................................................................196 
10.2.6. 
Informed Consent/Assent Process ............................................................................196 
10.2.7. 
Protocol Amendments ..............................................................................................197 
10.2.8. 
Protocol Deviations ..................................................................................................197 
10.2.9. 
Data Protection .........................................................................................................198 
10.2.10. 
Sample Retention and Future Biomedical Research ................................................198 
10.2.11. 
Dissemination of Clinical Study Data ......................................................................199 
10.2.12. 
Data Quality Assurance and Quality Control ...........................................................199 
10.2.13. 
Data Collection and Management ............................................................................200 
10.2.14. 
Source Documents ....................................................................................................200 
10.2.15. 
Retention of Records ................................................................................................201 
10.2.16. 
Study and Site Closure..............................................................................................201 
10.2.17. 
Publication Policy .....................................................................................................202 
10.2.18. 
BMI Charts for Boys and Girls .................................................................................202 
10.3. 
APPENDIX 3: Contraceptive Guidance ...................................................................204 
10.4. 
APPENDIX 4: Adverse Event of Special Interest Terms ........................................205 
10.5. 
APPENDIX 5: Protocol Amendment History ..........................................................208 
 

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LIST OF TABLES  
Table 1: 
Part 1 Study Objectives and Endpoints ......................................................................71 
Table 2: 
Part 2 Objectives and Endpoints .................................................................................76 
Table 3: 
Part 3 Objectives and Endpoints .................................................................................77 
Table 4: 
Non-Moderna COVID-19 Vaccine Available Under Emergency Use 
Authorization ..............................................................................................................86 
Table 5: 
Pause Rule Criteria, Events, and Thresholds ............................................................110 
Table 6: 
Solicited Adverse Reactions and Grades ..................................................................126 
Table 7: 
Analysis Sets .............................................................................................................145 
Table 8: 
Analysis Strategy for Safety Parameters ..................................................................146 
Table 9: 
Treatment Cohorts for the Long-term Analysis ........................................................149 
Table 10: Schedule of Assessments Part 1A, the Blinded Phase; Part 1B Open-label 
Observational Phase for Participants who Received mRNA-1273 in Part 1A .........162 
Table 11: Participant Decision Clinic Visit ..............................................................................166 
Table 12: Schedule of Assessments Part 1B, Open-label Observational Phase for 
Participants Who Previously Received Placebo .......................................................167 
Table 13: Schedule of Assessments Part 1C-1 – Homologous Booster Dose Phase ................169 
Table 14: Schedule of Assessments Part 1C-2 – Heterologous Booster Phase ........................172 
Table 15: Schedule of Assessments Part 2 (For Participants Who Receive The Booster 
Dose) .........................................................................................................................176 
Table 16: Schedule of Assessments Part 2 (For Participants Who Do Not Receive The 
Booster Dose) ...........................................................................................................183 
Table 17: Schedule of Assessments Part 3 (For Participants Who Receive Dose 2) ...............188 
Table 18: Schedule of Assessments Part 3 (For Participants Who Receive a Single 
Dose) .........................................................................................................................191 
Table 19: Medical Concepts that Qualify as Adverse Events of Special Interest ....................205 
LIST OF FIGURES  
Figure 1: 
Overall Design Schema ..............................................................................................80 
Figure 2: 
Study Schema (Part 1A, Blinded Phase) ....................................................................82 
Figure 3: 
Study Schema (Part 1B, Open-label Observational Phase) ........................................84 
Figure 4: 
Study Schema (Part 1C-1, Open-label Homologous Booster Dose 
Observational Phase) ..................................................................................................85 
Figure 5: 
Study Schema (Part 2 For Participants Who Receive The Booster Dose) .................88 

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Figure 6: 
Study Schema (Part 2 For Participants Who Do Not Receive The Booster 
Dose) ...........................................................................................................................88 
Figure 7: 
Study Schema Part 3 (For Participants Who Receive Dose 2) ...................................90 
Figure 8: 
Study Schema Part 3 (For Participants Who Receive a Single Dose) ........................91 
Figure 9: 
Surveillance for COVID-19 Symptoms and the Corresponding Clinical Data 
Pathways ...................................................................................................................122 
Figure 10: Schedule of Part 1A and Part 1B Participant Visits During the Part 1B 
Open-label Period .....................................................................................................166 
 

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LIST OF ABBREVIATIONS AND TERMS  
The following abbreviations and terms are used in this study protocol. 
Abbreviation or Specialist Term 
Definition 
Ab 
antibody 
AE 
adverse event 
AESI 
adverse events of special interest 
ANCOVA 
analysis of covariance 
AR 
adverse reaction 
bAb 
binding antibody 
BD 
booster dose 
BLA 
biologics license application 
BMI 
body mass index 
CBER 
Center for Biologics Evaluation and Research 
CD 
cluster of differentiation 
CDC 
Centers for Disease Control and Prevention 
CEAC 
cardiac event adjudication committee 
CFR 
Code of Federal Regulations 
CI 
confidence interval 
CoV 
coronavirus 
CoV S 
S protein SARS-CoV-2 
COVID-19 
coronavirus disease 2019 
CRO 
contract research organization 
CRP 
C-reactive protein 
CSR 
clinical study report 
DMID 
Division of Microbiology and Infectious Diseases 
DSMB 
Data Safety Monitoring Board 
DSPC 
1,2-distearoyl-sn-glycero-3-phosphocholine 
ECG (or EKG) 
electrocardiogram 
ECMO 
extracorporeal membrane oxygenation 
eCRF 
electronic case report form 
EDC 
electronic data capture 
eDiary 
electronic diary 
EOS 
end-of-study 
ERD 
enhanced respiratory disease 
ESR 
erythrocyte sedimentation rate 
EUA 
Emergency Use Authorization 
FAS 
full analysis set 

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Abbreviation or Specialist Term 
Definition 
FDA 
Food and Drug Administration 
FIO2 
fraction of inspired oxygen 
GCP 
Good Clinical Practice 
GLSM 
geometric least squares mean 
GM 
geometric mean 
GMC 
geometric mean concentration 
GMFR 
geometric mean fold rise 
GMR 
geometric mean ratio 
GMT 
geometric mean titer 
HCP 
healthcare practitioner 
HIV 
human immunodeficiency virus 
IA 
interim analysis 
IB 
investigator’s brochure 
ICF 
informed consent form 
ICH 
International Council for Harmonisation 
ICU 
intensive care unit 
IL-6 
interleukin 6 
IM 
intramuscular(ly) 
IP 
investigational product 
IRB 
institutional review board 
LAR 
legally acceptable representative(s) 
LDH 
lactic acid dehydrogenase 
LLOQ 
lower limit of quantification 
LNP 
lipid nanoparticle 
LTFU 
lost to follow-up 
MAAE 
medically attended adverse event 
MedDRA 
Medical Dictionary for Regulatory Activities 
MERS 
Middle East Respiratory Syndrome 
MIS-C 
multisystem inflammatory syndrome in children 
mITT 
modified intent-to-treat 
mRNA 
messenger RNA 
nAb 
neutralizing antibody 
NHP 
nonhuman primate 
NP 
nasopharyngeal 
PaO2 
partial pressure of oxygen 
PEG2000-DMG 
1-monomethoxypolyethyleneglycol-2,3-
dimyristylglycerol polyethylene glycol 2000 

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Abbreviation or Specialist Term 
Definition 
PP 
per-protocol 
PsVNA 
pseudovirus neutralizing antibody 
PsVNT 
pseudovirus neutralization titer 
QA 
quality assurance 
RT-PCR 
reverse transcriptase polymerase chain reaction 
S 
spike 
S2P 
S protein 
SAE 
serious adverse event 
SAP 
statistical analysis plan 
SARS 
Severe Acute Respiratory Syndrome 
SARS-CoV-2 
Severe Acute Respiratory Syndrome coronavirus 2 
SD 
standard deviation 
SM-102 
heptadecane-9-yl 8-((2-hydroxyethyl)(6-oxo-6-
(undecyloxy)hexyl)amino)octanoate 
SMC 
Safety Monitoring Committee 
SoA 
schedule of assessments 
SpO2 
oxygen saturation 
SRR 
seroresponse rate 
TEAE 
treatment-emergent adverse event 
Th1 
T helper cell 1 
Th2 
T helper cell 2 
USA 
United States of America 
VE 
vaccine efficacy 
VOC 
variant of concern 
WHO 
World Health Organization 
WOCBP 
woman of childbearing potential 

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1. 
INTRODUCTION  
1.1. 
Study Rationale  
Coronaviruses are a large family of viruses that cause illness ranging from the common cold to 
more severe diseases, such as MERS and SARS. Coronaviruses are zoonotic, meaning they are 
transmitted between animals and people. An outbreak of COVID-19 caused by SARS-CoV-2 
began in Wuhan, Hubei Province, China in December 2019 and has spread throughout China and 
to over 215 other countries, territories, and areas including the USA (WHO 2020a). On 
11 Mar 2020, the WHO officially declared COVID-19 a pandemic. 
Following the outbreak of COVID-19, ModernaTX, Inc. (hereafter referred to as the Sponsor) 
applied its mRNA vaccine platform and coronavirus research experience to rapidly develop the 
mRNA-1273 vaccine against SARS-CoV-2. At the time of study initiation, evidence suggested 
that the burden of COVID-19 has begun to increase in younger age groups (>408000 COVID-19 
cases and 88 deaths in children less than 18 years of age as of 21 Sep 2020), particularly as 
schools in the USA started to reopen for in person instruction (CDC 2022a). Adolescents also 
likely represented a segment of the population contributing toward sustained community 
transmission of SARS-CoV-2 as well as spread of SARS-CoV-2 within households given their 
mobility and less likelihood of compliance with mask wearing and social distancing 
(Fontanet et al 2020). 
Since then, there have been approximately 6.2 million COVID-19 cases and 772 deaths as of 
30 Aug 2022 in the USA (CDC 2022b) in adolescents 12-17 years of age. Since Mar 2020, 
approximately 1 in 4 hospitalized children and adolescents (0 to 17 years old) with COVID-19 
have required intensive care (CDC 2022c). While rates of severe disease have not increased 
since the start of the pandemic, the increase in absolute numbers of cases has added substantial 
burden, in terms of the increased number of emergency department and urgent care clinic 
encounters and hospitalizations in the adolescent population (Klein et al 2022; CDC 2022c). 
In addition to the increased incidence and hospitalizations observed, COVID-19 disease in 
children and adolescents can include MIS-C, a unique complication in conjunction with severe 
disease (Vogel et al 2021). MIS-C shares some common features with Kawasaki disease, and is 
defined as fever, laboratory evidence of inflammation, and involvement of ≥2 organ systems in 
an individual <21 years of age with no plausible alternative diagnosis and evidence of current or 
recent SARS-CoV-2 infection. MIS-C is also associated with cardiac complications. Through 
01 Aug 2022, 8798 cases of MIS-C have been reported in the USA, with 71 MIS-C related 
deaths reported. The median age of patients with MIS-C was 9 years (range 5 to 13 years) 
(CDC 2022d). 
Myocarditis has been well described as a complication of pediatric COVID-19. Children under 
16 years of age with COVID-19 are at an almost 37-fold higher risk of myocarditis than the 
uninfected age- and gender-matched control population (Boehmer et al 2020). Of note, the 
frequency of myocarditis due to COVID-19 is higher than that of vaccine-associated 
myocarditis. Additionally, the clinical syndrome of COVID-19 related myocarditis is more 
severe and clinically meaningful than vaccine-associated myocarditis. Patients with 
vaccine-associated myocarditis generally have a milder clinical course than patients with classic 

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myocarditis or MIS-C myocarditis, with a lower likelihood of cardiac dysfunction at presentation 
and more rapid recovery (Patel et al 2022). 
Long COVID, a sequela of COVID-19, affecting up to 20% of persons infected with 
SARS-CoV-2, has also been described in children, including in those with a mild infection. This 
syndrome is manifested by symptoms that can include fatigue, muscle and joint pain, insomnia, 
concentration difficulties, respiratory problems, persistence anosmia and ageusia, and cardiac 
palpitations that may occur within 6 months after infection (Buonsenso et al 2022; 
Buonsenso et al 2021; Dembinski et al 2021). 
Variants of concern such as Delta and Omicron have also emerged contributing to the substantial 
burden in the adolescent population. After the onset of the Omicron wave, the demographics of 
hospitalized patients with COVID-19 shifted to younger age groups (Abdullah et al 2022; 
Goga et al 2021; United Kingdom Health Security Agency 2022). Furthermore, the peak number 
of hospitalizations during Omicron was nearly 4 times greater than that observed during the 
Delta variant wave (Delahoy et al 2021; Marks et al 2022a; Marks et al 2022b). 
Taken together, a vaccine that prevents COVID-19 and its sequelae as well as SARS-CoV-2 
transmission in adolescents would be a crucial public health tool to help curb the pandemic. 
At the time the present study was initiated, no vaccine had been authorized or licensed to prevent 
SARS-CoV-2, and there was an urgent public health need to develop one, there being no proven 
therapy. The Sponsor initiated an accelerated development program for mRNA-1273 vaccine 
against SARS-CoV-2 infection (Section 1.2), and started a Phase 3 clinical study in the USA 
involving administration of mRNA-1273 vaccine 100 µg as both an initial dose and a second 
dose 28 days later (Section 1.2.2). Success criteria for early efficacy were met at first IA based 
on 95 adjudicated cases with a VE of 94.5% (95% CI: 86.5%, 97.8%; one-sided p-value 
< 0.0001), and EUA was granted for mRNA-1273 in the adult population. 
Data from the ongoing pivotal study mRNA-1273-P301 (Study P301) showed that mRNA-1273 
continued to induce durable protection: clinical efficacy against COVID-19 was maintained at 
93% through a median of approximately 5 months after the second dose. 
The primary objective for the Blinded Phase 2/3 study, mRNA-1273-P203 (Study P203), is to 
evaluate the safety and reactogenicity of a single dose level (100 g) of mRNA-1273 vaccine 
administered in 2 doses 28 days apart (Section 3.1) to an adolescent population. Specifically, the 
primary immunogenicity objective of the study is to infer effectiveness of mRNA-1273 (100 µg, 
2 doses 28 days apart) 28 days after Dose 2 of mRNA-1273 (Day 57) by comparison of immune 
responses in adolescents (aged ≥ 12 through < 18 years) to the young adult (≥18 to ≤25 year of 
age) cohort in Study P301, where efficacy was demonstrated. 
Interim data from the current Study P203 (based on a data snapshot of 08 May 2021) met the 
primary immunogenicity objective by demonstrating noninferiority of both the (i) GM value of 
serum nAb and (ii) the seroconversion rate from adolescent participants compared with those 
from young adults (aged 18 to 25 years) enrolled in the ongoing Phase 3 efficacy study 
(Study P301). These interim results supported administration of mRNA-1273 as two 100 µg 
doses 28 days apart in adolescents between ≥12 and 17 years of age. On 17 Jun 2022, the FDA 
granted EUA of the mRNA-1273 vaccine for adolescents 12 through 17 years of age. Global 
filings/authorizations down to 12 years of age have also occurred. 

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An additional objective of the current Study P203 is to evaluate safety and immunogenicity of a 
50 µg of mRNA-1273 given as a 2 dose primary series as well as when given as a homologous 
and heterologous booster vaccine. The rationale for these objectives is as follows: In Part A of 
Study mRNA-1273-P201 (Study P201), the time course and magnitude of antibody (both bAb 
and nAb) responses to mRNA-1273 was similar between 100 µg and 50 µg dose levels (both 
showing strong immunogenicity) at each postbaseline timepoint (Days 29, 43, 57, and 209), 
although the 100 µg dose group had numerically greater responses. In addition, recent interim 
results of the ongoing Study P201 support administration of a BD of vaccine. Adult participants 
in Study P201 received 2 doses of either 50 μg or 100 μg of mRNA-1273 and were administered 
a 50 μg booster of mRNA-1273 6 to 8 months after the second dose. Participants in Study P201 
who received the BD demonstrated enhanced immune responses to SARS-CoV-2 compared to 
preboost levels and met the noninferiority criteria stipulated in the FDA Guidance on EUA for 
Vaccines to Prevent COVID-19. Interim results from Study mRNA-1273-P205 (Study P205) 
also show that a 50 µg booster of mRNA-1273 increased nAb levels against Omicron 
approximately 37-fold compared to preboost levels. Available data also show that heterologous 
or mixed series of COVID-19 vaccine-induced high immune response in the adult population 
(Atmar et al 2021). Additionally, no new safety signals emerged upon administration of the BD 
in Study P201. Based on cumulative evidence, the benefit-risk profile of a BD of mRNA-1273 is 
favorable, particularly in light of increasing breakthrough disease with the emergence of the 
Delta and Omicron variants. 
The Sponsor also aims to evaluate the safety and immunogenicity of a 50 µg of mRNA-1273.222 
given as a 2 dose primary series in COVID-19 vaccine-naïve participants. Evaluation of the 
immunogenicity of 2 doses of the bivalent mRNA-1273.222 vaccine given 6 months apart which 
allows evaluation of immunogenicity post Dose 1 was prompted by following emerging data:  
a) Recent disease trends support the need for pediatric vaccination strategies that induce broader 
protection against VOCs (eg, Omicron variant) in addition to the ancestral SARS-CoV-2 strain, 
b) increasing prevalence of SARS-CoV-2 infection in the community (Clarke et al 2022), 
c) Study P205 data show that Omicron containing vaccine (ie, mRNA-1273.214) elicits strong 
immunogenicity in SARS-CoV-2 positive individuals (Chalkias et al 2022b), and d) durability of 
immune response post BD of a bivalent Beta containing vaccine (mRNA-1273.211) up to 6 
months with higher nAb responses in adults compared with mRNA-1273 against D614G, Beta, 
Omicron BA.1, and Delta variants (Chalkias et al 2022a). Results of Part 3 IA demonstrate 
robust immunogenicity of a single 50 µg mRNA-1273.222 dose. The pre-specified co-primary 
endpoints were also achieved, allowing inference of vaccine effectiveness of a single dose from 
the pivotal Study P301. Based on these results, Protocol Amendment 7 was initiated to remove 
Dose 2 administration of mRNA-1273.222 from Part 3. 
The Sponsor has developed mRNA-1273.222, a bivalent vaccine consisting of the mRNA that 
encodes for the prefusion stabilized spike glycoprotein of both the Wuhan-Hu-1 isolate of 
SARS-CoV-2 and the SARS-CoV-2 B.1.1.529, Omicron, variant. In November 2021, the SARS-
CoV-2 Omicron variant was detected in South Africa and was found to contain potential 
antibody escape site mutations such as K417N, T478K, E484A, and N501Y. 
The ability of the Omicron variant to escape prior immunity led to an unprecedented rise in 
COVID-19 infections and related hospitalizations, in adults as well as children, between 
December 2021 and February 2022. Real world effectiveness studies in adults conducted during 
the Omicron wave found a lower efficacy of the prototype vaccine against this new variant 

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(Ferdinands et al 2022; Tseng et al 2022). Moderna COVID-19 investigational variant-
containing vaccine candidates are being evaluated as booster vaccines in Study P205 including 
the BA.1 Omicron containing vaccine, mRNA-1273.214 and the Omicron BA.4/BA.5 containing 
vaccine mRNA-1273.222. These studies included adult participants, who previously received a 
primary series of mRNA-1273 (100 µg) and some participants in Part G and Part H of Study 
P205 who also previously received a 3rd dose (50 µg) of mRNA-1273, received a 4th dose 
(second booster given at a 50 µg) of bivalent Omicron containing mRNA-1273.214 and mRNA-
1273.222. Safety and Immunogenicity results from Study mRNA-1273-P205 are described in 
Section 1.2.2.3. 
1.2. 
Background and Overview  
The Sponsor’s scalable mRNA/LNP technology platform allowed for a rapid response to the 
COVID-19 pandemic and was used to develop mRNA-1273, a novel LNP-encapsulated 
mRNA-based vaccine against SARS-CoV-2. The Sponsor’s mRNA/LNP platform is based on 
the principle and observations that cells in vivo can take up mRNA, translate it, and then express 
protein viral antigen(s) on the cell surface. The delivered mRNA does not enter the cellular 
nucleus or interact with the genome, is nonreplicating, and is expressed transiently. Vaccine 
mRNA-1273 encodes for the full-length spike (S) protein SARS-CoV-2(CoV S). The CoV 
S protein mediates attachment and entry of the virus into host cells, by binding to the angiotensin 
converting enzyme 2 receptor followed by membrane fusion, making it a primary target for nAb 
that prevents infection (Johnson et al 2016; Wang et al 2015; Wang et al 2018; Chen et al 2017; 
Corti et al 2015; Yu et al 2015; Kim et al 2019; Widjaja et al 2019; Corbett et al 2020a; 
Ju et al 2020; Robbiani et al 2020). 
Worldwide approvals or authorizations have been issued for mRNA-1273 as a 2-dose 100 µg 
primary series or as a 50 µg BD in adults and in the adolescent age group.  
With the recent surge of a more divergent Omicron subvariant, the development of a bivalent 
mRNA-1273.222 vaccine was accelerated to address the current SARS-CoV-2 outbreak 
(Hastie et al 2021). 
In November 2021, the Omicron variant (B.1.1.529; BA.1) emerged as the most antigenically 
divergent variant to date that currently has more than 30 mutations in the S2P protein 
(Hastie et al 2021). In early 2022, new Omicron subvariants BA.4/BA.5 emerged which have 
their own unique and shared mutations with the BA.1. Leveraging the mRNA/LNP technology 
platform, the Sponsor initiated the development of modified COVID-19 vaccines against 
SARS-CoV-2 variants including the mRNA-1273.222 which contains 2 mRNAs: CX-024414 
encoding for the S-2P of Wuhan-Hu-1 and CX-034476 encoding for the S-2P of Omicron 
subvariants BA.4/BA.5. (See IB V8 Addendum 2). 
Moderna variant-containing bivalent booster vaccines (mRNA 1273.214 and mRNA-1273.222) 
have received approvals or authorizations globally in adults and in the adolescent age group. 
On 18 Apr 2023, the FDA amended the EUAs for the Moderna COVID-19 Vaccine (mRNA-
1273) and Moderna COVID-19 Vaccine, Bivalent (mRNA 1273.222) to simplify the vaccination 
schedule for most individuals. In that prior authorization, individuals 12 years of age and older 
who have not yet received a bivalent COVID-19 vaccine could receive a single dose of Moderna 
COVID-19, Bivalent (50 µg total mRNA), including individuals who have never received any 

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prior doses of COVID-19 vaccines. On 11 Sep 2023, the USA FDA approved the supplemental 
Biologics License Application for Spikevax® for ages 12 years and above, maintaining the 
recommendation for a single dose of the updated vaccine, Spikevax regardless of prior 
vaccination history. Moderna's updated COVID-19 vaccine contains spike proteins for the 
XBB.1.5 sublineage of SARS-CoV-2. Global regulatory filings for the updated COVID-19 
vaccine have also been initiated. 
1.2.1. 
Nonclinical Studies  
Nonclinical studies have demonstrated that CoV S proteins are immunogenic and S 
protein-based vaccines, including those based on mRNA delivery platforms, are protective in 
animals. Prior clinical studies of vaccines targeting related CoVs and other viruses have 
demonstrated that mRNA-based vaccines are safe and immunogenic. mRNA-1273 has shown 
preliminary evidence of protection against SARS-CoV-2 in studies in young mice 
(Corbett et al 2020a) and NHPs (Corbett et al 2020b). 
Nonclinical studies in mice, hamsters, and NHPs assessing the monovalent mRNA-1273.529, 
bivalent mRNA-1273.214 (contains the ancestral SARS-CoV-2 and the Omicron variant BA.1 
spike sequences), and bivalent mRNA-1273.222 (contains the ancestral SARS-CoV-2 and the 
Omicron variant BA.4/BA.5 spike sequences) vaccines are ongoing. These studies are designed 
to assess these vaccines as a primary series (2-dose) or as a booster (3rd or 4th dose) in animals 
previously vaccinated with mRNA-1273. Overall, interim data suggest that a primary series with 
a monovalent vaccine induces robust neutralization against the matched and closely related 
variants but does not induce significant neutralization against highly divergent SARS-CoV-2 
lineages. A bivalent vaccine, however, induces broader neutralization across divergent lineages. 
In these studies, no significant differences were measured in CD4 or CD8 cytokine production in 
mice that received mRNA-1273, mRNA-1273.529, or mRNA-1273.214. 
Mice were vaccinated with 2 doses of monovalent mRNA-1273, BA.1-matched monovalent 
mRNA-1273.529, or bivalent mRNA-1273.214, with 2 doses administered 3 weeks apart. At 
Day 36 (2 weeks after the second dose), robust serum nAb responses, determined via 
pseudovirus neutralization assay, were observed against Wuhan-1 D614G after a 2-dose primary 
series of 1 μg mRNA-1273, with slightly lower nAb titers observed against B.1.351 or 
B.1.617.2. Serum neutralizing activity, however, was significantly reduced against the BA.1 and 
BA.2 compared with Wuhan-1 D614G. Mice immunized with mRNA-1273.529 had high 
neutralization antibody titers against BA.1 and BA.2, but low levels of neutralization against 
Wuhan-1 D614G, B.1.351, and B.1.617.2. In mice vaccinated with the bivalent 
mRNA-1273.214, significant neutralization against both the prototype strain (Wuhan-1 D614G) 
and against BA.1 and BA.2 was measured, indicating that the bivalent vaccine affords broader 
neutralization across variants.  
In addition, mRNA-1273.214 and mRNA-1273.222 were studied in mice previously vaccinated 
with primary series of mRNA-1273. Mice were boosted with original (mRNA-1273), BA.1 
Omicron bivalent Omicron mRNA-1273.214, or Omicron BA.4/BA.5 bivalent mRNA-1273.222 
approximately 31 weeks between primary series and booster. Data shows increased 
immunogenicity of bivalent mRNA-1273.214 and mRNA-1273.222 vaccines (7- and 3-fold 
increase, respectively in BA.1 neutralization titers) & (4.2- and 4.5-fold increase, respectively in 
Omicron BA.4/BA.5 neutralization titers) after BD in mice whereas limited immunogenicity was 

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observed from the original mRNA-1273 vaccine. Bivalent vaccines also provide stronger 
protection from BA.5 infection in the lungs (Scheaffer et al 2022). 
In support of the development of mRNA-1273 for prophylaxis against SARS-CoV-2 infection, 
nonclinical immunogenicity, biodistribution, and safety studies have been completed with similar 
mRNA-based vaccines formulated in LNPs containing SM-102 (heptadecane-9-yl 
8-((2-hydroxyethyl)(6-oxo-6-(undecyloxy)hexyl)amino)octanoate), the novel proprietary lipid 
used in the mRNA-1273 LNP formulation. 
A detailed review of nonclinical experience with mRNA-1273 vaccine is provided in the IB. 
1.2.2. 
Clinical Studies  
The clinical development of mRNA-1273 vaccines to support its use in the adult population 
consists of 5 ongoing clinical trials being conducted in the USA: 
• Two Phase 1, open-label, dose ranging studies (Study 20-0003; NCT04283461; 
Study 21-0002, NCT04785144) sponsored by the NIAID. 
• Phase 2a, randomized, observer-blind, placebo-controlled, dose-confirmation study 
(Study mRNA-1273-P201; NCT04405076). 
• Phase 3 randomized, stratified, observer-blind, placebo-controlled study 
(Study mRNA-1273-P301; NCT04470427) to evaluate the efficacy, safety, and 
immunogenicity of the vaccine. 
• Phase 3b, open-label study (Study mRNA-1273-P304, NCT04860297) to evaluate the 
safety and immunogenicity of the vaccine in adult solid organ transplant recipients 
and healthy controls. 
In addition, 2 ongoing trials are being conducted in the pediatric population: 
• Phase 2/3 randomized, placebo-controlled safety and immunogenicity study of 
mRNA-1273 in children 12 to <18 years of age (Study mRNA-1273-P203 [current 
study]; NCT04649151). 
• Phase 2/3, study to evaluate the safety and immunogenicity of mRNA-1273 in 
children 6 months to <12 years of age (mRNA-1273-P204; NCT04796896). 
In addition, 4 ongoing trials are being conducted to support SARS-CoV-2 variants: 
• Study mRNA-1273-P205 (NCT04927065) is an open-label, Phase 2/3 study with 
multiple parts to evaluate the safety and immunogenicity of boosters for SARS-CoV-
2 variants. 
• Study mRNA-1273-P206 (NCT05584202) is a Phase 2, Part 1 open-label, Part 2 
randomized placebo-controlled study to evaluate the safety, reactogenicity and 
immunogenicity of the bivalent mRNA1273.214 vaccine for SARS-CoV-2 variants of 
concern in infants aged 12 weeks to <6 months. 
• Study mRNA-1273-P305 (NCT05249829) is a Phase 2/3, randomized, observer-
blind, active-controlled, multicenter study to evaluate the immunogenicity and safety 
of Omicron variant vaccines in comparison with mRNA-1273 (prototype) booster 
vaccine. 

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• Study mRNA-1273-P306 is a Phase 3 open-label study to evaluate the safety and 
immunogenicity of the mRNA1273.214 vaccine for SARS-CoV-2 variants of concern 
in participants aged 6 months to <6 years of age (Study mRNA-1273-P306; 
NCT05436834). 
1.2.2.1. 
Phase 1 Study DMID20-0003  
The safety and immunogenicity of mRNA-1273 were evaluated in Phase 1 (DMID 20-0003) and 
Phase 2 (P201) studies that were important to select and to confirm the dose of the vaccine used 
in the pivotal Phase 3 study. In Study 20-0003 (Phase 1), 2 doses of 100 μg or higher generated 
the highest titers of nAb or bAb with an acceptable safety profile, and this observation was the 
basis for selecting the 100 μg dose for use in the pivotal Phase 3 study. Importantly, the Ab 
levels after 2 doses of mRNA-1273 exceeded those from a pool of convalescent sera. 
Neutralizing activity was observed for the 100 μg mRNA-1273 dose as of Day 36 and was 
higher than that of the convalescent sera control group, and the median titers remained in the 
same range as the median titer in the convalescent sera control group at Day 119 across the age 
strata. In this study, the majority of the solicited ARs were mild or moderate. A higher incidence 
of severe solicited ARs was observed with the 250 μg dose (in the 18–55-year age cohort) 
compared with the lower doses (25 μg, 50 μg, and 100 μg); thus, the mRNA-1273 250 μg dose 
was not evaluated in participants ≥56 years of age. One severe unsolicited AE related to 
mRNA-1273 and 1 severe clinically meaningful elevation in serum lipase related to mRNA-1273 
were also observed with the 250 μg dose (in the 18–55-year age cohort). Additionally, in 
Study 20-0003, Th1-directed CD4+ T-cells were observed to be induced across age groups, with 
limited indication of a Th2-directed response, and similar responses were observed among all 
age groups for the 100 μg dose. The predominance of a Th1-directed T-cell profile helps mitigate 
concern of the risk of enhanced disease associated with Th2-driven pathophysiology. 
1.2.2.2. 
Phase 2 Study mRNA-1273-P201  
Study P201 is an ongoing Phase 2a, safety, reactogenicity, and immunogenicity study in healthy 
adults that provided confirmation of the immunogenicity of both the 100 μg and 50 µg doses. 
The study was designed as a randomized, observer-blind, placebo-controlled dose-confirmation 
study (Part A). Two mRNA-1273 dose levels, 50 μg and 100 μg, and placebo were evaluated in 
2 age cohorts: Cohort 1 enrolled participants ≥18 to < 55 years old (300 participants), and 
Cohort 2 enrolled participants ≥ 55 years old (300 participants). A total of 600 participants 
received either mRNA-1273 or placebo according to a 1:1:1 randomization ratio, ie, within each 
age cohort, 100 participants each received mRNA-1273 50 μg, mRNA-1273 100 μg, or placebo. 
An amendment to the Study 201 protocol adapted the study design to include open-label 
interventional phases (Part B and Part C). Part B allowed unblinding of participants and offered 
2 injections of mRNA-1273 in an open-label manner, 28 days apart, to all participants who 
received placebo in Part A. Part B also offered a single BD of mRNA-1273 (50 μg) to 
participants who received 1 or 2 doses of mRNA-1273 (50 μg or 100 μg) in Part A. Part C was 
prompted by the need to proactively prepare for vaccination strategies that might induce broader 
protection, including against emerging variants of SARS-CoV-2 such as B.1.351. Part C enrolled 
participants from Study 301 who received 2 doses of mRNA-1273 100 μg at least 6 months 
prior. Part C participants received a single injection of mRNA-1273.351 (20 μg or 50 μg) or 
mRNA-1273.351 mixture (50 μg total – 25 μg of mRNA-1273 and 25 μg of mRNA-1273.351). 

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mRNA-1273 demonstrated an acceptable safety profile in the participant population enrolled in 
this study at both dose levels and both age cohorts, as observed through 6 months after the 
second injection. Vaccination with mRNA-1273 in Study 201 resulted in robust immune 
responses to SARS-CoV-2 in participants 18 years and older at both dose levels, and persistence 
of immune response was observed up to 6 months after the second injection in Part A of the 
study. In Part A of Study 201, the time course and magnitude of antibody (both bAb and nAb) 
responses to mRNA-1273 was similar between 100 μg and 50 μg dose levels at each postbaseline 
timepoint (Days 29, 43, 57, and 209), although the 100 μg dose group had numerically greater 
responses (and was the dose selected for the pivotal Phase 3 efficacy study). In Part B of 
Study 201, administration of a 50 μg BD of mRNA-1273 6 months or more after the primary 
series improved the immune responses to 1.7-fold the peak achieved after the primary 
vaccination series in the current mRNA-1273-P301 study, where efficacy of mRNA-1273 
against COVID-19 was demonstrated. Safety data based on preliminary results for 50 μg BDs of 
mRNA-1273 (selected participants in Part B) or mRNA-1273.351 (Part C Cohort 1) are 
available. Percentages of participants with solicited local and systemic AEs were similar in the 
group who received mRNA-1273.351 as a BD compared to those who received mRNA-1273 
vaccine as a BD. The majority of solicited local and systemic AEs were mild (Grade 1) or 
moderate (Grade 2). The frequency of any Grade 3 solicited local or systemic AE was 15% (3 of 
20 participants) after the BD of mRNA-1273 and 10.5% (2 of 19 participants) after the BD of 
mRNA-1273.351. There were no Grade 4 solicited local or systemic AEs. The most common 
solicited local AE was injection site pain after injection in both groups (68.4% for the 
mRNA-1273.351 vaccine and 90.0% for the mRNA-1273 vaccine). The most common solicited 
systemic AEs after the BD of the mRNA-1273.351 vaccine were fatigue (36.8%), headache 
(36.8%), myalgia (31.6%), and arthralgia (21.1%). The most common solicited systemic AEs 
after the BD of the mRNA-1273 vaccine were fatigue (70.0%), headache (55.0%), arthralgia 
(50.0%), and myalgia (45.0%). Fever was reported after the BD of mRNA-1273 in 3 of 
20 participants (15%) but not after the BD of mRNA-1273.351 (0 of 19 participants). There were 
no SAEs reported in this study. 
1.2.2.3. 
Phase 2/3 Study mRNA-1273-P205  
Part G of Study P205 will evaluate the immunogenicity, safety, and reactogenicity of the 
mRNA-1273.214 vaccine (contains the ancestral SARS-CoV-2 and the Omicron variant spike 
sequences) when administered as a single BD to adult participants who have previously received 
the mRNA-1273 primary series as well as a BD. The results of the mRNA-1273.214 vaccine will 
be compared to the immunogenicity induced after an mRNA-1273 BD, in individuals who also 
previously received the 2-dose primary series of mRNA-1273. Interim results are available. 
Part H of the study will evaluate the immunogenicity, safety, and reactogenicity of the 
mRNA-1273.222 vaccine (contains the ancestral SARS-CoV-2 and the Omicron variant 
BA.4/BA.5 spike sequences) when administered as a single BD to adult participants who have 
previously received the mRNA-1273 primary series as well as a BD. The results of the 
mRNA-1273.222 vaccine will be compared with the immunogenicity induced after an 
mRNA-1273 BD in participants who also previously received the 2-dose primary series of 
mRNA-1273. Results from this study are pending. 

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Immunogenicity Study (mRNA-1273-P205) – Day 29 Interim Results of Study 
mRNA-1273.214: 
The bivalent booster vaccine, 50 μg mRNA-1273.214 contains equal amounts of the mRNA 
sequence for the S protein, 25 μg of the ancestral SARS-CoV-2 and 25 μg of the Omicron spike 
mRNA sequence. The immunogenicity of 50 μg mRNA-1273.214 was evaluated in Part G of the 
P205 Study when administered as a second BD in adults who previously received 2 doses of 
100 μg mRNA-1273 as a primary series and a single BD of 50 μg mRNA-1273. The IA of 
Study P205 showed that all primary and key secondary immunogenicity objectives were met 
based on the prespecified testing sequence. The mRNA-1273.214 dose of 50 μg elicited a 
superior nAb response against Omicron and a noninferior neutralizing response against the 
ancestral SARS-CoV-2 strain compared with the 50 μg mRNA-1273 28 days after the BD. 
Specifically, in the primary analysis set, defined as participants without evidence of prior 
SARS-CoV-2 infection, the estimated Day 29 nAb GMTs (95% CI) against the ancestral 
SARS-CoV-2 (D614G) were 6422.3 (5990.1, 6885.7) and 5286.6 (4887.1, 5718.9) 28 days after 
the mRNA-1273.214 and mRNA-1273 BDs, respectively. The GMR (97.5% CI) was 1.22 (1.08, 
1.37), meeting the prespecified criterion for noninferiority (lower bound of 97.5% CI >0.667). 
The Day 29 SRR (95% CI) against ancestral SARS-CoV-2 was 100% (98.9, 100 and 98.6, 100) 
28 days after in the mRNA-1273.214 and mRNA-1273 groups, respectively, with an SRR 
difference of 0, meeting the noninferiority criterion (lower bound of CI >-10%). In participants 
who received the mRNA-1273.214, who were SARS-CoV-2 positive, baseline nAb GMT against 
the ancestral strain as well as 28 days post BD were higher than those who were SARS-CoV-2 
negative (Chalkias et al 2022b). 
The estimated Day 29 nAb GMTs against Omicron were 2479.9 (2264.5, 2715.8) and 1421.2 
(1283.0, 1574.4) in the mRNA-1273.214 and mRNA-1273 groups, respectively. The GMR 
(97.5% CI) was 1.75 (1.49, 2.04), which met the prespecified superiority criterion (lower bound 
of CI >1). The Day 29 Omicron SRRs (95% CI) were 100% (98.9, 100) and 99.2% (97.2, 99.9) 
in the mRNA-1273.214 and mRNA-1273 groups, respectively. The SRR difference (97.5% CI) 
was 1.5% (-1.1, 4.0), meeting noninferiority criteria (lower bound of CI >-10%). 
All immunogenicity endpoints were also met based on an analysis that included participants with 
and without evidence of prebooster SARS-CoV-2 infection. 
Additionally, in the primary analysis set (PPSI – Neg, reflecting participants without prior 
SARS-CoV-2 infection), the observed GMTs (95% CI) against Omicron BA.4/BA5 GMTs 
(95% CI) prebooster were 115.6 (98.5, 135.6) and increased to 727.4 (632.9, 836.1) at 28 days 
after the BD for mRNA-1273.214 with a GMFR (95% CI) of 6.3 (5.7, 6.9). The GMTs 
(95% CIs) in the mRNA-1273.214 group were 139.7 (119.5, 163.3) prebooster and 492.1 (431.1, 
561.9) 28 days after the BD, and the GMFR (95% CI) was 3.5 (3.2, 3.9). The GMR (95% CI) for 
the comparison of mRNA-1273.214 50 μg BD with the mRNA-1273 50 μg BD was 1.69 (1.51, 
1.90) with the lower bound of the CI >1 (See IB V8 Addendum 2). 
On the basis of these results, the mRNA-1273.214 (50 μg) elicited superior nAb responses 
against the Omicron subvariants BA.4, BA.5 compared with mRNA-1273 (50 μg) (nominal α of 
0.05) and the BA.4, BA.5 nAb response was consistently higher in the mRNA-1273.214 group 
compared to the mRNA-1273 group in participants with and without prior SARS-CoV-2 
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Immunogenicity Study (mRNA-1273-P205) – Interim Results (mRNA-1273.222) 
Participants received 50-μg of mRNA-1273 (n=376) or mRNA-1273.222 (n=511) as second 
booster doses. Omicron BA.4/BA.5 and ancestral SARS-CoV-2 D614G neutralizing antibody 
geometric mean titers (GMTs [95% confidence interval]) after mRNA-1273.222 (2324.6 
[1921.2-2812.7] and 7322.4 [6386.2-8395.7]) were significantly higher than mRNA-1273 (488.5 
[427.4-558.4] and 5651.4 (5055.7-6317.3) respectively, at day 29 post-boost in participants with 
no prior SARS-CoV-2-infection. A randomly selected subgroup (N=60) of participants in the 
mRNA-1273.222 group also exhibited cross-neutralization against the emerging omicron 
variants BQ.1.1 and XBB.1. No new safety concerns were identified with mRNA-1273.222. 
Vaccine effectiveness was not assessed in this study; in an exploratory analysis 1.6% (8/511) of 
mRNA-1273.222 recipients had Covid-19 post-boost (Chalkias et al 2022c). 
Safety: 
The safety and reactogenicity of 50 μg mRNA-1273.214 was evaluated in the Part G of Study 
P205 when administered as a second BD in adults who previously received 2 doses of 100 μg 
mRNA-1273 as a primary series and a single BD of 50 μg mRNA-1273. The 50 μg 
mRNA-1273.214 second BD was administered a median of 136 days after a first BD of the 
50 μg mRNA-1273 and had a median follow-up duration of 43 days (range 22 to 51 days). The 
50 μg mRNA-1273.214 was well-tolerated and had a reactogenicity profile similar to that of the 
50 μg mRNA-1273 when given as a second BD. The incidence of ARs after immunization with 
50 μg mRNA-1273.214 was also similar or lower relative to that of a first BD of 50 μg 
mRNA-1273 and relative to the second dose of the 100 μg mRNA‑1273 primary series. No new 
safety signals were identified. 
The overall occurrence of solicited local ARs within 7 days following second BDs was 79.4% 
and 79.5% in the mRNA-1273.214 and mRNA-1273 groups, respectively. The most common 
solicited local AR was injection site pain for any Grade event in both groups (77.3% and 76.6% 
in the mRNA-1273.214 and mRNA-1273 group, respectively). The incidences of systemic ARs 
were 70.3% in the mRNA-1273.214 and 66.1% in the mRNA- 1273 groups, and the most 
frequent ARs for any Grade event were fatigue (54.9% and 51.4%), headache (43.9% and 
41.1%), and myalgia (39.6% and 38.6%) in the mRNA-1273.214 and mRNA-1273 groups, 
respectively. The majority of solicited ARs were mild to moderate (Grades 1-2) for both groups. 
The incidence of Grade 3 events was 8.0% in both groups, with the most common being fatigue 
(3.4% and 3.1%) and myalgia (2.3% and 3.7%), for the mRNA-1273.214 and mRNA-1273 
groups, respectively. No Grade 4 events occurred in either group (See IB V8 Addendum 2). 
The unsolicited AEs were reported in 18.5% of participants in the mRNA-1273.214 group and 
20.7% in the mRNA-1273 group regardless of the relationship to vaccination up to 28 days after 
the second BD. In the mRNA-1273.214 group, 2 (0.5%) participants each experienced 2 SAEs 
(prostate cancer and traumatic fracture) and 1 (0.3%) participant in the mRNA-1273 group 
reported an SAE of spinal osteoarthritis within 28 days of the BD; none were assessed by the 
investigator to be related to study vaccination. MAAEs were 9.8% in the mRNA-1273.214 and 
13.8% in the mRNA-1273 groups up to 28 days after the second BD vaccination. There were no 
fatal events or AEs leading to study discontinuation that were related to vaccination as assessed 
by investigators. As of the data cutoff date, no deaths or AEs of special interest, including cases 
of myocarditis or pericarditis, occurred, and 1 additional SAE (Grade 3, nephrolithiasis) 

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considered unrelated to study vaccination was reported in the mRNA-1273.214 group. 
Additional details of results of clinical studies are provided in the IB (IB V8 Addendum 2). 
1.2.2.4. 
Phase 3 Study mRNA-1273-P301  
Currently, a Phase 3 pivotal, randomized, placebo-controlled, observer-blind clinical Study P301 
is being conducted in participants 18 years of age and older who are at an increased risk of 
COVID-19 disease. In addition, prespecified cohorts of participants who were either ≥65 years 
of age or 18 to <65 years of age with comorbid medical conditions were included. A total of 
30351 participants were followed for a median of 92 days (range: 1-122) for the development of 
COVID-19 disease. Success criteria for early efficacy were met at first IA based on 95 
adjudicated cases with a VE of 94.5% (95% CI: 86.5%, 97.8%; one-sided p-value <0.0001). 
Study P301 is expected to provide immunogenicity data where an Ab threshold of protection 
against COVID-19 will be estimated. 
In Study P301, solicited ARs were reported more frequently among vaccine participants than 
placebo participants. The most frequently reported ARs after any dose in the vaccine group were 
pain at the injection site (92.0% any Grade; 6.1% Grade ≥3), fatigue (70% any Grade; 10.1% 
Grade ≥3), headache (64.7% any Grade; 5.7% Grade ≥3), myalgia (61.5% any Grade; 9.1% 
Grade ≥3) and chills (45.4% any Grade; 1.4% Grade ≥3). The majority of local and systemic 
ARs had a median duration of 1 to 3 days. Overall, there was a higher reported rate of some ARs 
in younger age groups: the incidence of axillary swelling/tenderness, fatigue, headache, myalgia, 
arthralgia, chills, nausea/vomiting, and fever was higher in adults aged 18 to <65 years than in 
those aged 65 years and above. Grade 3 solicited local ARs were more frequently reported after 
Dose 2 than after Dose 1. In the participants who received the vaccine, solicited systemic ARs 
were reported numerically more frequently by vaccine participants after Dose 2 than after 
Dose 1. Grade 3 systemic ARs (fatigue, myalgia, arthralgia, and headache) were reported more 
frequently after Dose 2 than after Dose 1. Unsolicited AEs and SAEs were reported at generally 
similar rates in participants who received mRNA-1273 and placebo from the first dose until the 
last observation. Unsolicited AEs that occurred in ≥1% of study participants who received 
mRNA-1273 and at a rate at least 1.5-fold higher rate than placebo, were 
lymphadenopathy-related events (1.1% of versus 0.6%). All of the lymphadenopathy events are 
similar to the axillary swelling/tenderness in the injected arm reported as solicited ARs. 
Hypersensitivity AEs were reported in 1.5% of vaccine recipients and 1.1% of placebo 
recipients. Hypersensitivity events in the vaccine group included injection site rash and injection 
site urticaria, which are likely related to vaccination. There have been no cases of severe 
hypersensitivity or anaphylactic reactions reported immediately after vaccination in the trial to 
date. There were 3 reports of Bell’s palsy in the mRNA-1273 vaccine group (one of which was 
an SAE), which occurred 22, 28, and 32 days after vaccination, and one in the placebo group, 
which occurred 17 days after vaccination. The currently available information on Bell’s palsy is 
insufficient to determine a causal relationship with the vaccine. There were 2 SAEs of facial 
swelling in vaccine recipients with a history of injection of dermatological fillers. The onset of 
swelling was reported 1 and 2 days, respectively, after vaccination and was likely related to 
vaccination. There was 1 SAE of intractable nausea and vomiting in a participant with prior 
history of severe headache and nausea requiring hospitalization. This event occurred 1 day after 
vaccination and was likely related to vaccination. 

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There were no other notable patterns or numerical imbalances between treatment groups for 
specific categories of AEs (including other neurologic, neuro-inflammatory, and thrombotic 
events) that would suggest a causal relationship to mRNA-1273. 
The Sponsor submitted a data package to FDA on 30 November 2020 for consideration of EUA. 
FDA granted an EUA for mRNA-1273 for use in adults 18 years of age and older on 18 
December 2020. 
Efficacy and safety results based on the final analysis of Part A with a database lock of 
04 May 2021 are provided in the IB. The results are generally comparable to the IA. On 
25 Aug 2021, Moderna announced that it had completed the rolling submission process for its 
BLA to the FDA for the full licensure of the Moderna COVID-19 vaccine (mRNA-1273) for 
active immunization to prevent COVID-19 in individuals 18 years of age and older. On 
31 Jan 2022, mRNA-1273 was granted full licensure by the USA FDA. mRNA-1273 has been 
showing durable efficacy of 93% through 6 months after the second dose. 
1.2.2.5. 
Study mRNA-1273-P203 - Interim Results  
Interim data from the current Part 1A of Study P203 (based on a data snapshot of 08 May 2021) 
show that the primary immunogenicity objective was met by demonstrating noninferiority of 
both the (i) GM value of serum nAb and (ii) the seroconversion rate from adolescent participants 
compared with those from young adults (aged 18 to 25 years) enrolled in the ongoing Phase 3 
efficacy study (Study P301). The GMR of adolescent (Study P203) to young adult (Study P301) 
nAb titers at Day 57 was 1.077 (95% CI: 0.939, 1.236), meeting the 1.5-fold noninferiority 
criterion (ie, lower bound of the 95% CI for GMR is >0.667). The difference in adolescent to 
young adult nAb SRRs at Day 57 was 0.2 (95% CI: -1.8, 2.4), meeting the 10% noninferiority 
criterion (lower bound of the 95% of the SRR difference is ≥-10%). In addition, results of VE 
against COVID-19, defined using either the “Study P301 case definition” or the “CDC case 
definition”, and conducted starting 14 days after Dose 1 or Dose 2 were all similar to the 94.1% 
VE observed 14 days post Dose 2 in the pivotal Study P301. Overall, local reactogenicity was 
higher and systemic reactogenicity was lower to mRNA-1273 in adolescents compared with that 
observed in the adult mRNA-1273-P301 study. Both solicited local and systemic ARs were more 
commonly reported by participants in the mRNA-1273 group and systemic ARs generally 
increased after Dose 2. While the majority of these solicited ARs were Grade 1 or Grade 2, there 
was a higher frequency of Grade 3 or higher solicited ARs in the mRNA-1273 group than in the 
placebo group after Dose 1 and Dose 2. The majority of the solicited ARs in participants who 
received mRNA-1273 occurred within the first 1 to 2 days after any dose and generally persisted 
for a median of 1 to 3 days. The frequency of reported solicited ARs were generally similar and 
there were no notable differences in the reported rates of unsolicited AEs observed between 
participants aged ≥ 12 to < 16 years and participants aged ≥16 to <18 years. 
Unsolicited treatment-emergent AEs (TEAEs) up to 28 days after any dose were more common 
in the mRNA-1273 group than in the placebo group. Imbalances in unsolicited TEAEs up to 
28 days after any dose was primarily attributable to events related to reactogenicity. The 
incidence of MAAEs within 28 days of injection was generally similar between the mRNA-1273 
and placebo groups. The incidence of unsolicited severe TEAEs and serious TEAEs in the 
28 days after any dose was low overall and generally similar in participants who received 
mRNA-1273 and those who received placebo. Unsolicited TEAEs, including MAAEs, up to 

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28 days after any dose assessed by the investigator as related to study treatment were more 
frequently reported in the mRNA-1273 group than in the placebo group. 
Data from interim data cut of 31 Jan 2022 showed consistent immunogenicity and safety results 
as the first interim results (08 May 2021). The evidence from the 08 May 2021 data cutoff infers 
effectiveness, suggesting that mRNA-1273 is effective in preventing COVID-19, and the known 
and potential benefits of mRNA-1273 when used to prevent COVID‑19 outweigh the known and 
potential risks. 
The updated data collected as of 31 Jan 2022 included: (i) VE of the blinded phase updated as of 
31 May 2021; (ii) COVID-19 cases as of 31 Jan 2022; and (iii) safety data from all mRNA-1273 
recipients for the blinded and open‑label phases of the study. 
Vaccine efficacy through 31 May 2021 was 100% (95% CI: 61.2%, not estimated [NE]) using 
the P301 case definition and 89.9% (95% CI: 51.0%, 98.9%) using the CDC case definition. The 
updated analysis confirms results provided in the EUA Amendment submitted on 09 Jun 2021 
based on the 08 May 2021 data cutoff). Beyond 31 May 2021, the loss of placebo participants 
precluded meaningful analysis of VE. Long-term assessment of monthly incidence rates among 
all participants who received mRNA-1273 as randomized and remained on study up to 
31 Jan 2022 (combined blinded and unblinded) shows low monthly incidence rates of 
COVID-19 until November 2021. Not unexpectedly, an increase in COVID-19 incidence rates 
was observed in December 2021 and January 2022, when the Omicron variant prevailed. 
Neutralizing activity against the Omicron variant was evaluated in a small subset (N=20 each 
study) of serum samples randomly selected from adults (≥18 years) in the pivotal P301 study, 
and from adolescents (≥12 to <18 years) in Study P203 following a 2-dose regimen of 100 μg 
mRNA-1273 and from children (6 to <12 years) in Study mRNA-1273-P204 after 2 doses of 
50 μg mRNA-1273. In adolescents, nAb measured against Omicron was present in all 
participants (100%) 4 weeks after Dose 2. The GMT against Omicron was 11.8-fold lower than 
that measured against D614G among adolescents. Compared with adults, adolescent GMTs were 
1.5- and 3.8‑fold higher for D614G and the Omicron variant, respectively (Girard et al 2022). 
mRNA-1273 was found to be generally safe in clinical Study P203 with no new safety signals in 
either the 08 May 2021 initial EUA Amendment data cutoff or the longer-term safety cut of 
31 Jan 2022. The overall safety profile observed in the adolescent study (Study P203) was 
generally consistent with the findings to date in the Phase 3 Study P301 in adults aged ≥18 years. 
In the long-term safety follow-up, SAEs were reported for 22/2577 participants (0.9%) overall. 
No SAEs were assessed by investigators as related to study vaccine and there were no fatal 
events. MAAEs were reported for 1002/2577 participants (38.9%) overall. MAAEs considered 
by the investigator to be related to mRNA-1273 were reported for 26 participants (1.0%). The 
incidence of MAAEs reflects the Omicron surge. Three participants in the mRNA-1273 group 
discontinued study vaccine because of a TEAE. AESIs were reported for 13 participants. In the 
open-label, crossover phase, there was 1 probable case of myocarditis (adjudicated by cardiac 
endpoint adjudication committee) observed in the Study P203 clinical program which occurred 
1 day following second dose but did not require hospitalization and completely resolved by 
8 days postvaccination with no sequelae at 5 months of follow-up (Study mRNA-1273-P203 data 
on file). 

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Interim results from Part 1C-1 as of data cutoff date of 15 Aug 2022 (DBL of 27 Oct 2022) 
demonstrate effectiveness of a mRNA-1273 BD (50 µg) in adolescents 12 to <18 years inferred 
based on comparison of adolescent nAb responses to those post-mRNA-1273 primary series in 
young adults in Study P301. Results echo the successful immunobridging of the primary series 
for this same age group. Prespecified NI immunogenicity criteria were met for adolescents 
(GMR point estimate 5.071 and lower bound of the 95% CI of 4.477; SRR difference point 
estimate of 0.7% and lower bound of the 95% CI of -0.8%) allowing effectiveness of a 50 μg BD 
of mRNA-1273 in adolescents 12 to <18 years to be inferred. There were no new safety findings 
observed in the mRNA-1273 Booster Phase of Study P203 and in general, the BD showed less 
reactogenicity than the primary series. Most solicited ARs were reported within 2 days, were 
Grade 1 or 2 and lasted a median of 2 to 3 days. Pain was the most frequently reported solicited 
local AR and headache and fatigue were the most frequently reported solicited systemic AR. 
There were no SAEs or AESIs reported in the 28 days after BD. There were no reported deaths 
or cases of MIS-C, and even with the enhanced surveillance implemented in this study, no TEAE 
indicative of myocarditis or pericarditis was identified. Up to the time of data cutoff 
(15 Aug 2022), the unsolicited AE profile, including SAEs and AESIs, demonstrated events 
typically observed in an adolescent population during the COVID-19 pandemic (CSR 
Addendum 1). 
Results from Part 2 data snapshot as of 01 May 2023, show robust nAb responses 28 days after 
1 dose of 50 µg mRNA-1273 in baseline SARS-CoV-2 positive participants. After 28 days post 
dose 1 of 50 µg mRNA-1273, the GMC levels in the adolescent baseline-positive participants 
increased to 18-fold higher than the baseline GMC levels (GMC=6053.2 [95%CI: 4495.8, 
8150.1]). Despite the higher baseline nAb responses observed in adolescent baseline-positive 
participants, the GMC post dose 1 of 50-µg mRNA-1273 was observed to be higher than those 
observed post primary series in baseline SARS-CoV-2 negative young adults in Study P301 
(GMC=1400.4 [95% CI: 1272.7, 1541.0) with a GMR of 4.322 (95% CI: 3.274, 5.707). The 
seroresponse rates were comparable between the Study P203 adolescents (97.5%, n=39/40) and 
Study P301 young adults (99.3%, n=292/294), with SRR difference of -1.8% (95% CI: -12.2%, 
0.8%). Administration of the second dose did not increase the neutralizing antibody response to 
the degree which was observed in baseline SARS-CoV2 negative participants (mRNA-1273 
Part 2 Data Memo). 
Results from Part 3 IA (data cutoff of 05 Jun 2023) demonstrate that after 28 days post Dose 1 of 
50 µg mRNA-1273.222, the GMC levels against the Omicron BA.4/BA.5 in the adolescent 
baseline-positive participants increased to 18-fold higher than the baseline GMC levels 
(GMC=2771.0 [95% CI: 2500.8, 3070.3]). The GMC post Dose 1 of 50 µg mRNA-1273.222 
was observed to be higher than those observed post-primary series in baseline SARS-CoV-2 
negative young adults in Study P301 (GMC=56.6 [95% CI: 54.5, 58.8). The rate of seroresponse 
against the Omicron BA.4/BA.5 was high (94.7%) in study P203 Part 3 adolescents whereas 
none of the P301 young adults seroconverted against the Omicron BA.4/BA.5, 28 days after 
Dose 2 of the 100 µg mRNA-1273 primary series; the difference in SRR was 94.7% (95% CI: 
91.1%, 96.9%). In addition, the GMC levels against the ancestral strain in the adolescent 
baseline-positive participants increased to 13.6-fold 28 days post Dose 1 compared to baseline 
GMC levels (Day 29 GMC=7187.1 [95% CI: 6495.3, 7952.7]). The GMC post Dose 1 of 50 µg 
mRNA-1273.222 in adolescent baseline-positive participants was observed to be higher than 
those observed post-primary series in baseline SARS-CoV-2 negative young adults in 

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Study P301 (GMC=1692.3 [95% CI: 1537.4, 1862.7). The rates of seroresponse against the 
ancestral strain were comparable between the study P203 Part 3 adolescents (94.6%) and study 
P301 young adults (99.3%); the difference in SRR was -4.7% (95% CI: -8.4%, -2.1%). The 
GMR of Study P203 Part 3 Day 29 GMC against Omicron BA.4/BA.5 compared with young 
adults in Study P301, Day 57 GMC was 48.953 (95% CI: 44.209, 54.206), meeting the 
superiority criterion (ie, lower bound of the 95% CI >1.0). The GMR of Study P203 Part 3 
Day 29 GMC against ancestral strain compared with young adults in Study P301, Day 57 GMC 
was 4.247 (95% CI: 3.693, 4.884), meeting the noninferiority criterion (ie, lower bound of the 
95% CI >0.667). The prespecified success criteria for the primary immunogenicity objective 
were met, thus enabling the inference of vaccine effectiveness of the single 50 µg 
mRNA-1273.222 in Study 203 Part 3 from that observed in Study P301. 
Based on Part 3 IA results and the approval of the updated monovalent COVID-19 vaccine 
containing the spike proteins for the XBB.1.5 sublineage of SARS-CoV-2, the second dose in 
Part 3 was removed. 
In the post-EUA period, anaphylaxis has been reported following mRNA-1273 administration. 
There have been very rare reports of myocarditis and pericarditis occurring after vaccination 
with COVID-19 mRNA vaccines. A detailed review of the clinical experience with LNPs 
containing SM-102 (mRNA vaccines and placebo) is provided in the IB. 
1.3. 
Benefit/Risk Assessment  
1.3.1. 
Potential Benefits from Participation  
The following benefits may accrue to participants: 
• The mRNA-1273 and mRNA-1273.222 vaccines may be effective against COVID-19 
including disease caused by variants of concern. 
• Participants will have a baseline (Day 1) evaluation for SARS-CoV-2 infection and 
ongoing surveillance for COVID-19 throughout the study. 
• The study will contribute to the development of a vaccine against COVID-19 for 
adolescents. 
1.3.2. 
Risks to Study Participants and Risk Mitigation  
Immediate systemic allergic reactions (eg, anaphylaxis) can occur following any vaccination. 
These reactions are very rare and are estimated to occur once per 450,000 vaccinations for 
vaccines that do not contain allergens such as gelatin or egg protein (Zent et al 2002). As a 
precaution, all participants will remain under observation at the study site for at least 30 minutes 
after injection. 
Vasovagal syncope (fainting) can occur before or after any vaccination, is usually triggered by 
the pain or anxiety caused by the injection and is not related to the substance injected. Therefore, 
it is important that standard precautions and procedures are followed to avoid injury from 
fainting. 
IM injection with other mRNA vaccines manufactured by the Sponsor containing the SM-102 
lipid formulation commonly results in a transient and self-limiting local inflammatory reaction. 

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This typically includes pain, erythema (redness), or swelling (hardness) at the injection site, 
which are mostly mild to moderate in severity and usually occur within 24 hours of injection. 
The majority of local and systemic solicited ARs observed after injection with mRNA-1273 at 
the 100 µg dose level have been mild to moderate in severity (Section 1.2.2). The most 
commonly reported systemic ARs were headache, myalgia, fatigue, chills, and fever. In the 
majority of cases, the reactions resolved spontaneously within several days. 
There is a theoretical risk that active vaccination to prevent SARS-CoV-2 infection may cause a 
paradoxical increase in the risk of COVID-19. This possibility is based on the rare phenomenon 
of vaccine-associated disease enhancement, which was first seen in the 1960s with 2 vaccines 
made in the same way (formalin-inactivated whole virus) and designed to protect children 
against infection with respiratory syncytial virus (Chin et al 1969) or measles virus 
(Fulginiti et al 1967). Disease enhancement has also been proposed as a possible explanation for 
cases of more serious disease associated with dengue vaccination (Thomas and Yoon 2019; 
WHO 2019). 
In order to address this theoretical risk, animal studies were performed in young and aged 
wild-type mice and rhesus macaques (NHPs). These studies were designed to capture 
immunogenicity endpoints that would be predictive of ERD and also to evaluate if, at protective 
or subprotective dose levels of mRNA-1273, evidence of disease enhancement would be 
observed after challenge of the animals with SARS-CoV-2. These nonclinical studies 
demonstrated that mRNA-1273 is safe and well-tolerated in different animal species, is 
immunogenic; drives a robust SARS-CoV-2-specific Ab, neutralization, and Th1-directed CD4 
T-cell response; fully protects animals from challenge at dose levels as low as 1 μg/dose in mice 
and 30 μg/dose in NHPs; and does not lead to ERD at protective or subprotective dose levels 
(Corbett et al 2020a; Corbett et al 2020b). Clinical immunogenicity data from the DMID Phase 1 
study of mRNA-1273 demonstrated high levels of nAbs and Th1-polarized CD4+ T-cell 
responses (Jackson et al 2020), consistent with the immunogenicity observed in these nonclinical 
studies. These data suggest that a paradoxical increase in the risk of disease, while not 
eliminated, is likely to be low. 
In individuals 18 years of age and older, there have been very rare reports of myocarditis and 
pericarditis occurring after vaccination with Moderna COVID-19 vaccine. The majority of the 
cases have been reported in young males shortly after the second dose of the vaccine. These are 
typically mild cases and individuals tend to recover within a short time following standard 
treatment and rest (Gargano et al 2021). One probable case of myocarditis was reported in this 
study with features consistent with this typical mild, short-lived pattern 
(Study mRNA-1273-P203 data on file). Recent data from an observational study (Wong 2022) 
conducted in 4 large US administrative health plan claims databases covering more than 
100 million persons, (OptumServe, HealthCore, Blue Health Intelligence, and CVS Health) 
observed no statistical difference in risk rates of myocarditis/pericarditis following any dose of 
2 mRNA COVID-19 vaccines. Moreover, recently published data from a health care 
organization in Israel estimated the incidence of myocarditis due to COVID‐19 infection as 
11.0 cases per 100,000 persons (95% CI: 5.6–15.8), compared to the nearly five-fold lower 
incidence of myocarditis observed following the 2nd dose of mRNA-1273 (highest incidence 
rate) at 2.17 per 100,000 person-days (95% CI: 1.55-3.04) (Wong 2022). Other studies also show 
that myocarditis cases related to COVID‐19 infection revealed a higher mortality rate and rate of 

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severe complications compared to myocarditis cases following vaccination with a COVID-19 
mRNA vaccine (Patel et al 2022). Moreover, infection with SARS‐CoV‐2 has more adverse 
events beyond myocarditis, including many carrying significant risk for death. 
In adults, the AEs after receiving a third dose of mRNA-1273 are described in Section 1.2.2. In 
general, solicited local and systemic ARs after the BD (Study P201) were comparable to what 
had been observed with the primary series (Study P301). Preliminary report from a heterologous 
booster study in adults show reactogenicity and adverse events were similar across booster 
groups (Atmar et al 2021). 
1.3.3. 
Overall Benefit/Risk Conclusion  
All participants in Part 1 will receive a single dosage of 100 g mRNA-1273 vaccine or placebo 
administered in 2 doses 28 days apart (Section 3.1). Participants in Part 1A who received 
mRNA-1273 will be offered an option to receive a third BD of 50 µg of mRNA-1273 at least 
5 months from second dose in Part 1C-1. Participants in Part 1A who received placebo will be 
offered to receive a single dose of 100 µg mRNA-1273 vaccine administered in 2 doses 28 days 
apart in Part 1B and a third BD of 50 µg of mRNA-1273 at least 5 months from second dose in 
Part 1C-1. All participants in Part 1C-2 will receive a single BD of 50 µg of mRNA-1273. 
Participants in Part 2 will receive a single dosage of 50 µg mRNA-1273 vaccine administered in 
2 doses 28 days apart with or without a booster dose. Participants in Part 3 will receive 1 or 
2 doses of 50 µg bivalent mRNA-1273.222 vaccine. 
Safety will be monitored throughout the study (Section 7.6). 
Considering the limited number of approved vaccines for COVID-19, the participants’ risk of 
COVID-19 outside the study during a pandemic, and the nonclinical and clinical data to date, the 
Sponsor considers the potential benefits of participation to exceed the risks. 

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2. 
OBJECTIVES AND ENDPOINTS  
The objectives which will be evaluated in this study and endpoints associated with each objective 
are provided in Table 1, Table 2, and Table 3. 
Table 1: 
Part 1 Study Objectives and Endpoints  
Objectives 
Endpoints 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety and reactogenicity 
of 100 µg mRNA-1273 vaccine 
administered in 2 doses 28 days apart 
• 
Solicited local and systemic ARs through 7 days 
after each injection 
• 
Unsolicited AEs through 28 days after each 
injection 
• 
MAAEs through the entire study period 
• 
SAEs through the entire study period 
• 
AESIs through the entire study period 
• 
Vital sign measurements 
• 
Physical examination findings 
• 
To infer efficacy of mRNA-1273 
(100 µg, 2 doses 28 days apart), serum 
Ab responses obtained 28 days after the 
second injection of mRNA-1273 
(Day 57) will be either: 
− 
Evaluated against an accepted Ab 
threshold of protection against 
COVID-19 (if established in 
Study P301) 
− 
Compared in primary vaccine 
response as measured by GM values 
of serum Ab and SRR in Study P203 
with those obtained from young 
adult recipients (18 to 25 years of 
age) of mRNA-1273 in the clinical 
endpoint efficacy trial (Study P301) 
• 
The proportion of participants with a serum Ab 
level at Day 57 ≥ an Ab threshold of protection1 
• 
The primary vaccine response as measured by GM 
value of serum Ab level and SRR from Study P203 
vaccine recipients at Day 57 compared with those 
obtained from young adult recipients (18 to 25 
years of age) at Day 57 in the clinical endpoint 
efficacy trial (Study P301)2 
1. 
If an accepted serum Ab threshold of vaccine 
protection against COVID-19 is available, this 
analysis will form the basis to infer efficacy 
2. 
If a threshold is not available, efficacy will be 
inferred based on establishing noninferiority 
of adolescent (12 to < 18 years; this clinical 
study) to adult GM values of serum Ab and 
SRR obtained in Study P301 (GM value 12 to 
< 18 years / GM value 18 to 25 years) 
Secondary Objectives 
Secondary Endpoints 
• 
To evaluate the persistence of the 
immune response of mRNA-1273 
vaccine (100 µg) administered in 2 doses 
28 days apart, as assessed by the level of 
SARS-CoV-2 S2P-specific bAb through 
1 year after Dose 2 
• 
The GM value of SARS-CoV-2 S2P-specific bAb 
on Day 1, Day 57 (1 month after Dose 2), Day 209 
(6 months after Dose 2), and Day 394 (1 year after 
Dose 2) 
• 
To evaluate the persistence of the 
immune response of mRNA-1273 
vaccine (100 µg) administered in 2 doses 
• 
The GM values of SARS-CoV-2-specific nAb on 
Day 1, Day 57 (1 month after Dose 2), Day 209 

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Objectives 
Endpoints 
28 days apart, as assessed by the level of 
nAb through 1 year after Dose 2 
(6 months after Dose 2), and Day 394 (1 year after 
Dose 2)  
• 
To evaluate the effect of mRNA-1273 on 
the incidence of SARS-CoV-2 infection 
compared with the incidence among 
placebo recipients 
• 
The incidence of SARS-CoV-2 infection 
(symptomatic or asymptomatic infection) counted 
starting 14 days after the second dose of IP 
• 
SARS-CoV-2 infection will be defined in 
participants with negative SARS-CoV-2 at 
baseline: 
− 
bAb level against SARS-CoV-2 nucleocapsid 
protein negative at Day 1 that becomes positive 
(as measured by Roche Elecsys) at Day 57 or 
later, OR 
− 
Positive RT-PCR counted starting 14 days after 
the second dose of IP  
• 
To evaluate the incidence of 
asymptomatic SARS-CoV-2 infection 
after vaccination with mRNA-1273 or 
placebo  
• 
The incidence of asymptomatic SARS-CoV-2 
infection measured by RT-PCR and/or bAb levels 
against SARS-CoV-2 nucleocapsid protein (by 
Roche Elecsys) counted starting 14 days after the 
second dose of IP in participants with negative 
SARS-CoV-2 at baseline 
• 
To evaluate the incidence of COVID-19 
after vaccination with mRNA-1273 or 
placebo. COVID-19 is defined as clinical 
symptoms consistent with SARS-CoV-2 
infection AND positive RT-PCR for 
SARS-CoV-2 
• 
The incidence of the first occurrence of COVID-19 
starting 14 days after the second dose of IP, where 
COVID-19 is defined as symptomatic disease 
based on the following criteria: 
− 
The participant must have experienced at least 
TWO of the following systemic symptoms: 
Fever (≥ 38ºC/≥ 100.4ºF), chills, myalgia, 
headache, sore throat, new olfactory and taste 
disorder(s), OR 
− 
The participant must have experienced at least 
ONE of the following respiratory 
signs/symptoms: cough, shortness of breath or 
difficulty breathing, OR clinical or 
radiographical evidence of pneumonia; AND 
− 
The participant must have at least 1 NP swab, 
nasal swab, or saliva sample (or respiratory 
sample, if hospitalized) positive for SARS-
CoV-2 by RT-PCR 
Exploratory Objectives 
Exploratory Endpoints 
• 
To evaluate the genetic and/or 
phenotypic relationships of isolated 
SARS-CoV-2 strains to the vaccine 
sequence 
• 
Alignment of genetic sequence of viral isolates 
with that of the vaccine sequence and comparison 
of bAb and nAb titers against isolated strain 
relative to prototype vaccine strain 

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Objectives 
Endpoints 
• 
To describe the ratio or profile of 
specific bAb relative to nAb in serum 
• 
Relative amounts or profiles of S protein-specific 
bAb and specific nAb levels/titers in serum 
• 
To characterize the clinical profile and 
immune responses of participants with 
COVID-19 or with SARS-CoV-2 
infection 
• 
Description of clinical severity and immune 
responses of participants who are identified as 
infected by SARS-CoV-2 (COVID-19) 
• 
To evaluate the incidence of 
asymptomatic SARS-CoV-2 infection 
after vaccination with mRNA-1273 or 
placebo in participants with serologic 
evidence of infection at baseline 
• 
GM value and GMFR of bAb levels against 
SARS-CoV-2 nucleocapsid protein (quantitative 
IgG) and % of participants with 2x, 3x, and 4x rise 
of bAb relative to baseline 
Exploratory Objectives for Part 1B: 
Exploratory Endpoints for Part 1B: 
• 
To evaluate the safety of 2 doses of 
mRNA-1273 
• 
MAAEs through the entire study period 
• 
SAEs through the entire study period 
• 
AESIs through the entire study period 
• 
AEs leading to discontinuation from study 
participation through the last day of study 
participation 
• 
To evaluate the incidence of 
SARS-CoV-2 or COVID-19 after 
vaccination with mRNA-1273  
• 
The incidence of SARS-CoV-2 infection 
(symptomatic or asymptomatic infection) counted 
starting 14 days after the second dose of mRNA-
1273 
• 
To evaluate the incidence of asymptomatic 
SARS-CoV-2 infection after vaccination with 
mRNA-1273 measured by RT-PCR and/or bAb 
levels against SARS-CoV-2 nucleocapsid protein 
(by Roche Elecsys) counted starting 14 days after 
the second dose in participants with negative 
SARS-CoV-2 at baseline 
• 
The incidence of the first occurrence of 
symptomatic COVID-19 starting 14 days after the 
second dose of mRNA-1273 
Objectives for Part 1C-1 – Homologous 
Booster Dose 
Endpoints for Part 1C-1 – Homologous Booster 
Dose 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety of the 50 μg BD 
of mRNA-1273 
• 
Solicited local and systemic ARs through 7 days 
after BD 
• 
Unsolicited AEs through 28 days after BD 
injection 
• 
MAAEs through the entire study period 
• 
SAEs through the entire study period 

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Objectives 
Endpoints 
• 
AESIs through the entire study period 
• 
AEs leading to discontinuation from study 
participation post BD through the last day of study 
participation 
• 
To infer effectiveness of 50 μg of 
mRNA-1273 booster by establishing 
noninferiority of Ab response after the 
BD compared to the primary series of 
mRNA-1273. GM values of serum Ab 
and SRR of postbooster in Study P203 
compared with primary series from 
young adult (18 to 25 years of age) 
recipients of mRNA-1273 in the clinical 
endpoint efficacy trial (Study P301) 
Coprimary endpoints: 
• 
GM value of postbooster (post Dose 3) Ab against 
ancestral strain in Study P203 as compared to post 
primary series (post Dose 2) against ancestral strain 
in the young adults in Study P301 
• 
SRR of postbooster/Dose 3 from baseline (pre 
Dose 1) as compared to post Dose 2 from baseline 
(pre Dose1) against ancestral strain in the young 
adults in Study P301, using 4-fold rise definition 
− 
Seroresponse is defined as Ab value change 
from baseline (pre Dose 1) below the LLOQ to 
≥4 × LLOQ, or at least a 4-fold rise if baseline 
is ≥LLOQ  
Key Secondary Objective 
Key Secondary Endpoint 
• 
To evaluate immune response elicited by 
the 50 μg prototype booster of mRNA-
1273 against variant(s) of interest 
• 
GM value of postbooster (post Dose 3) Ab against 
circulating strain as compared to post primary 
series (post Dose 2) against circulating strain 
• 
SRR of postbooster/Dose 3 from baseline (pre 
Dose 1) as compared to post Dose 2 from baseline 
(pre Dose1) against circulating strain using 4-fold 
rise definition 
Exploratory Objectives 
Exploratory Endpoints 
• 
To evaluate the persistence of the 
immune response of the BD of mRNA-
1273 vaccine (50 µg) as assessed by the 
level of SARS-CoV-2 S2P specific bAb 
through 1 year after BD 
• 
The GM values of SARS-CoV-2 S2P specific bAb 
on BD-Day 1, BD-Day 29 (1 month after BD), 
BD-Day 181 (6 months after BD), and BD-Day 
361 (1 year after BD) 
• 
To evaluate the persistence of the 
immune response of the BD of mRNA-
1273 vaccine (50 µg) as assessed by the 
level of nAb through 1 year after BD 
• 
The GM values of SARS-CoV-2-specific nAb on 
BD-Day 1, BD-Day 29 (1 month after BD), 
BD-Day 181 (6 months after BD), and 
BD-Day 361 (1 year after BD) 
• 
To evaluate the incidence of 
SARS-CoV-2 infection or COVID-19 
after vaccination with mRNA-1273 
• 
The incidence of SARS-CoV-2 infection 
(symptomatic or asymptomatic infection) counted 
starting 14 days after BD of mRNA-1273 
• 
To evaluate the incidence of asymptomatic 
SARS-CoV-2 infection after vaccination with 
mRNA-1273 measured by RT-PCR and/or bAb 
levels against SARS-CoV-2 nucleocapsid protein 
(by Roche Elecsys) counted starting 14 days after 

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Objectives 
Endpoints 
BD in participants with negative SARS-CoV-2 at 
baseline or prebooster 
• 
The incidence of the first occurrence of 
symptomatic COVID-19 starting 14 days after BD 
of mRNA-1273 
Objectives for Part 1C-2 – Heterologous 
Booster Dose 
Endpoints for Part 1C-2 – Heterologous Booster 
Dose 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety of the 50 μg BD 
of mRNA-1273 in participants who 
received non-Moderna COVID-19 
primary series vaccination 
• 
Solicited local and systemic ARs through 7 days 
after BD 
• 
Unsolicited AEs through 28 days after BD 
injection 
• 
MAAEs through the entire study period 
• 
SAEs through the entire study period 
• 
AESIs through the entire study period 
• 
AEs leading to discontinuation from study 
participation post BD through the last day of study 
participation 
• 
To evaluate immune response elicited by 
the 50 μg booster of mRNA-1273 in 
participants who received non-Moderna 
COVID-19 primary series vaccination 
• 
GM value of postbooster Ab (BD-Day 29) against 
ancestral strain 
Key Secondary Objective 
Key Secondary Endpoint 
• 
To evaluate immune response elicited by 
the 50 μg prototype booster of mRNA-
1273 against variant(s) of interest in 
participants who received non-Moderna 
COVID-19 primary series vaccination 
• 
GM value of postbooster Ab (BD-Day 29) against 
circulating strain 
Exploratory Objectives 
Exploratory Objectives 
• 
To evaluate the persistence of the 
immune response of the BD of mRNA-
1273 vaccine (50 µg) as assessed by the 
level of SARS-CoV-2 S2P specific bAb 
through 1 year after BD in participants 
who received non-Moderna COVID-19 
primary series vaccination 
• 
The GM values of SARS-CoV-2 S2P specific bAb 
on BD-Day 1, BD-Day 29 (1 month after BD), 
BD-Day 181 (6 months after BD), and BD-Day 
361 (1 year after BD) 
• 
To evaluate the persistence of the 
immune response of the BD of mRNA-
1273 vaccine (50 µg) as assessed by the 
level of nAb through 1 year after BD in 
participants who received non-Moderna 
COVID-19 primary series vaccination 
• 
The GM values of SARS-CoV-2-specific nAb on 
BD-Day 1, BD-Day 29 (1 month after BD), 
BD-Day 181 (6 months after BD), and 
BD-Day-361 (1 year after BD) 

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Objectives 
Endpoints 
• 
To evaluate the incidence of 
SARS-CoV-2 infection or COVID-19 
after booster vaccination with mRNA-
1273 in participants who received non-
Moderna COVID-19 primary series 
vaccination 
• 
The incidence of SARS-CoV-2 infection 
(symptomatic or asymptomatic infection) counted 
starting 14 days after BD of mRNA-1273 
• 
To evaluate the incidence of asymptomatic 
SARS-CoV-2 infection after vaccination with 
mRNA-1273 measured by RT-PCR and/or bAb 
levels against SARS-CoV-2 nucleocapsid protein 
(by Roche Elecsys) counted starting 14 days after 
BD in participants with negative SARS-CoV-2 at 
baseline or prebooster 
• 
The incidence of the first occurrence of 
symptomatic COVID-19 starting 14 days after BD 
of mRNA-1273 
Abbreviations: Ab = antibody; AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; 
bAb = binding antibody; BD = booster dose; COVID-19 = coronavirus disease 2019; GM = geometric mean; 
GMFR = geometric mean fold rise; IP = investigational product; LLOQ = lower limit of quantification; 
MAAE = medically attended adverse event; nAb = neutralizing antibody; NP = nasopharyngeal; 
RT-PCR = reverse transcriptase polymerase chain reaction; S = spike; S2P = S protein; SAE = serious adverse 
event; SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2; SRR = seroresponse rate. 
Table 2: 
Part 2 Objectives and Endpoints  
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety and reactogenicity 
of the 50 μg mRNA-1273 vaccine 
administered in 2 doses 28 days apart.  
• 
Solicited local and systemic ARs through 7 days 
after each injection 
• 
Unsolicited AEs through 28 days after each 
injection 
• 
MAAEs through the entire study period 
• 
SAEs through the entire study period 
• 
AESIs through the entire study period 
• 
AEs leading to discontinuation from study 
participation from Dose 1 through the last day of 
study participation  
• 
To evaluate immune response elicited by 
the 50 μg mRNA-1273 vaccine 
administered in 2 doses 28 days apart. 
• 
GM value of post Dose 2 (Day 57) Ab against 
ancestral strain in Part 2 of Study P203 
• 
SRR of post Dose 2 from baseline (pre Dose 1) in 
Part 2 of Study P203 against ancestral strain, using 
4-fold rise definition 
− 
Seroresponse is defined as Ab value change 
from baseline (pre Dose 1) below the LLOQ to 
≥4 × LLOQ, or at least a 4-fold rise if baseline 
is ≥LLOQ 

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Exploratory Objectives 
Exploratory Endpoints 
• 
To evaluate the persistence of the 
immune response of 50 μg mRNA-1273 
vaccine administered in 2 doses 28 days 
apart as assessed by the level of SARS-
CoV-2 S2P specific bAb through 1 year 
after Dose 2 
• 
The GM values of SARS-CoV-2 S2P specific bAb 
on Day 1, Day 57 (1 month after Dose 2), Day 209 
(6 months from Dose 2), Day 394 (1 year from 
Dose 2) 
• 
To evaluate the persistence of the 
immune response of the 50 μg mRNA-
1273 vaccine as assessed by the level of 
nAb through 1 year after Dose 2 
• 
The GM values of SARS-CoV-2-specific nAb on 
Day 1, Day 57 (1 month after Dose 2), Day 209 
(6 months from Dose 2), Day 394 (1 year from 
Dose 2) 
• 
To evaluate the incidence of 
SARS-CoV-2 infection or COVID-19 
after vaccination with mRNA-1273. 
• 
The incidence of SARS-CoV-2 infection 
(symptomatic or asymptomatic infection) counted 
starting 14 days after Dose 2 of mRNA-1273 
• 
To evaluate the incidence of asymptomatic 
SARS-CoV-2 infection after vaccination with 
mRNA-1273 measured by RT-PCR and/or bAb 
levels against SARS-CoV-2 nucleocapsid protein 
(by Roche Elecsys) counted starting 14 days after 
Dose 2 in participants with negative SARS-CoV-2 
at baseline 
• 
The incidence of the first occurrence of 
symptomatic COVID-19 starting 14 days after 
Dose 2 of mRNA-1273 
Abbreviations: Ab = antibody; AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; 
bAb = binding antibody; COVID-19 = coronavirus disease 2019; GM = geometric mean; GMFR = geometric 
mean fold rise; LLOQ = lower limit of quantification; MAAE = medically attended adverse event; 
nAb = neutralizing antibody; RT-PCR = reverse transcriptase polymerase chain reaction; S2P = S protein; 
SAE = serious adverse event; SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2; 
SRR = seroresponse rate. 
Table 3: 
Part 3 Objectives and Endpoints  
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety and reactogenicity 
of the 50 μg mRNA-1273.222 vaccine 
administered as 1 dose. 
• 
Solicited local and systemic ARs through 7 days after 
injection. 
• 
Unsolicited AEs through 28 days after injection. 
• 
MAAEs through the entire study period. 
• 
SAEs through the entire study period. 
• 
AESIs through the entire study period. 
• 
AEs leading to withdrawal from study participation 
from Dose 1 through the last day of study 
participation. 
• 
To infer effectiveness of the 50 µg 
mRNA-1273.222 vaccine based on 
immune response against SARS-CoV-2 
• 
GM value of post Dose 1 (Day 29) of mRNA-
1273.222 Ab against SARS-CoV-2 VOC (Omicron 
BA.4/BA.5) in adolescents who are baseline SARS-

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Primary Objectives 
Primary Endpoints 
VOC (Omicron BA.4/BA.5) and 
ancestral strain obtained 28 days post 
Dose 1 in the baseline SARS-CoV-2 
positive population. 
CoV-2 positive in Part 3 of Study P203 compared to 
that of post primary series of mRNA-1273 (post 
Dose 2 [Day 57] of 100 µg) in young adults 18 to 
25 years of age who are baseline SARS-CoV-2 
negative in Study P301 (superiority testing). 
• 
GM value of post Dose 1 (Day 29) of mRNA-
1273.222 Ab against ancestral strain in adolescents 
who are baseline SARS-CoV-2 positive in Part 3 of 
Study P203 compared to that of post primary series 
of mRNA-1273 (post Dose 2 [Day 57] of 100 µg) in 
young adults 18 to 25 years of age who are baseline 
SARS-CoV-2 negative in Study P301 (noninferiority 
testing). 
Secondary Objectives 
Secondary Endpoints 
• 
To evaluate immune response elicited by 
50 µg mRNA-1273.222 vaccine 
administered as 1 dose based on immune 
responses against Omicron BA.4/BA.5 
and ancestral strain obtained 28 days 
post Dose 1. 
• 
SRR of post Dose 1 (Day 29) from baseline (pre 
Dose 1) against Omicron BA.4/BA.5 in adolescents 
who are baseline SARS-CoV-2 positive in Part 3 of 
Study P203 compared to that of post primary series 
of mRNA-1273 (post Dose 2 [Day 57] of 100 µg) in 
adults 18 to 25 years of age in Study P301. 
• 
SRR of post Dose 1 (Day 29) from baseline (pre 
Dose 1) against ancestral strain in adolescents who 
are baseline SARS-CoV-2 positive in Part 3 of Study 
P203 compared to that of post primary series of 
mRNA-1273 (post Dose 2 [Day 57] of 100 µg) in 
adults 18 to 25 years of age in Study P301. 
Note: Seroresponse is defined as an Ab value change 
from baseline (pre Dose 1) below the LLOQ to ≥4 × 
LLOQ, or at least a 4-fold rise if baseline is ≥ LLOQ. 
• 
To evaluate immune response elicited by 
50 μg mRNA-1273.222 vaccine 
administered as 1 dose against other 
variant(s) of interest obtained 28 days 
post Dose 1. 
• 
GM value of post Dose 1 (Day 29) of mRNA-
1273.222 Ab against other variant(s) of interest in 
Part 3 of Study P203 as compared to that of post 
primary series of mRNA-1273 (post Dose 2 [Day 57] 
of 100 µg) in adults 18 to 25 years of age in Study 
P301. 
Exploratory Objectives 
Exploratory Endpoints 
• 
To evaluate the persistence of the 
immune response of 50 μg 
mRNA-1273.222 vaccine, as assessed by 
the level of SARS-CoV-2 S2P specific 
bAb through 6 months after Dose 1. 
• 
The GM values of SARS-CoV-2 S2P specific bAb 
on Day 1, Day 29 (1 month after Dose 1), Day 85 
(3 months after Dose 1), and Day 181 (6 months after 
Dose 1). 
• 
To evaluate the persistence of the 
immune response of the 50 μg mRNA-
1273.222 vaccine as assessed by the 
• 
The GM values of SARS-CoV-2-specific nAb on 
Day 1, Day 29 (1 month after Dose 1), Day 85 
(3 months after Dose 1), and Day 181 (6 months after 
Dose 1). 

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Primary Objectives 
Primary Endpoints 
level of nAb through 6 months after 
Dose 1. 
• 
To evaluate the incidence COVID-19 
after vaccination with mRNA-1273.222. 
• 
The incidence of the first occurrence of symptomatic 
COVID-19 starting 14 days after Dose 1 of mRNA-
1273.222. 
Abbreviations: Ab = antibody; AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; 
bAb = binding antibody; COVID-19 = coronavirus disease 2019; GM = geometric mean; LLOQ = lower limit of 
quantification; MAAE = medically attended adverse event; nAb = neutralizing antibody; RT-PCR = reverse 
transcriptase polymerase chain reaction; S2P = S protein; SAE = serious adverse event; SARS-CoV-2 = Severe 
Acute Respiratory Syndrome coronavirus 2; SRR = seroresponse rate; VOC = variant of concern. 

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3. 
STUDY DESIGN  
3.1. 
General Design  
This study is split into 3 parts and the overall design schematic can be seen in Figure 1. 
Figure 1: 
Overall Design Schema 
 
Abbreviation: BD = booster dose. 
a. 
For participants who receive a single dose. 
b. 
For participants who receive Dose 2. 
3.1.1. 
Part 1 Study Design  
This is a three-part, Phase 2/3 study: Part 1A, Part 1B, and Part 1C. Participants in Part 1A, the 
Blinded Phase, are blinded to their treatment assignment. 
Part 1B, the Open-label Observational Phase of this study, is designed to offer participants who 
received placebo in Part 1A of this study and who meet the EUA eligibility criteria an option to 
receive mRNA-1273 in an open-label fashion (Figure 3). Participants who received mRNA-1273 
(100 µg) in Part 1A of this study will proceed to Part 1B after they are unblinded and will 
continue to follow the Part 1A SoA (Table 10). Part 1C-1, the Homologous Booster Dose Phase, 
is designed to offer participants in Part 1A and Part 1B, and who are at least 5 months from the 
last dose, the option to request a BD of 50 µg mRNA-1273. Part 1C-2, the Heterologous Booster 
Phase, is designed to provide participants who completed non-Moderna primary COVID-19 
vaccination series under EUA (ie, Pfizer) a 50 µg BD of mRNA-1273 at least 3 months from the 
last dose. 

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Participants who received mRNA-1273 in Part 1A will be in the study approximately 25 months 
if a BD is received in Part 1C-1, which includes 1 month for Screening (Day ˗28 to Day 1), up to 
12 months for dosing (on Day 1, Day 29, and Day 209 for BD), and 12 months for follow-up. 
Participants who received placebo in Part 1A will be in the study for approximately 25 months 
total if a BD is received in Part 1C-1, which includes approximately 9 months in Part 1A and 
approximately 4 months of follow-up following their second dose of mRNA-1273 in Part 1B 
before entering Part 1C-1 or before BD is received; or approximately 12 months of follow-up. 
Participants that decline unblinding or decline to receive a BD will be in the study approximately 
14 months total, which includes 1 month for Screening (Day -28 to Day 1), 1 month for dosing 
(on Day 1 and Day 29), and 12 months for follow-up. 
Participants in Part 1C-2 will be in the study for approximately 12 months total, which includes 
7 days for Screening (Day -7 to Day 1), 1 day of dosing (BD-Day 1), and 12 months of 
follow-up. 
This study will be conducted in compliance with the protocol, GCP, and all applicable regulatory 
requirements. 
3.1.1.1. 
Part 1A, the Blinded Phase  
The blinded phase of this study is a randomized, observer-blind, placebo-controlled study 
intended to infer the effectiveness of mRNA-1273 in an adolescent population aged 12 to 
< 18 years. The study includes 2 arms: (i) 100 µg of mRNA-1273, and (ii) placebo. 
Approximately, 3000 participants between 12 to < 18 years of age will be randomly assigned in a 
2:1 ratio to receive mRNA-1273 (n=2000) or placebo (n=1000). 
The schematic of study arms and major study events for Part 1A is illustrated in Figure 2 and the 
SoA for Part 1A is located in Table 10. 
The goal of the study is to seek an indication for use of mRNA-1273 (100 µg IM, given as 
2 injections, 28 days apart) in the 12 to < 18 years age group. The basis for demonstrating 
vaccine effectiveness is proposed to be met by serum Ab response measured in this adolescent 
age group. The approach to inferring vaccine effectiveness will depend on whether an accepted 
serum Ab threshold conferring protection against COVID-19 has been established. If an Ab 
threshold of protection has been established, effectiveness will be inferred based on the 
proportion of adolescent study participants with serum Ab levels (on Day 57) that meet or 
exceed the Ab threshold. If an Ab threshold of protection has not been established, effectiveness 
will be inferred by demonstrating noninferiority of both (i) the GM value of serum nAb and (ii) 
the SRR from adolescent participants compared with those from young adults (18 to 25 years of 
age) enrolled in the ongoing clinical endpoint efficacy trial (Study P301). The statistical 
parameters to infer effectiveness are described in Section 2. 
This study in adolescents will monitor all participants for a total of 12 months following the 
second dose of vaccine or placebo. Safety assessments will include solicited ARs (7 days after 
each injection), unsolicited AEs (28 days after each injection), MAAEs, SAEs, and AESIs 
(including MIS-C) throughout the study period. 
Blood samples will be collected from all participants at baseline (Day 1), Day 57 (28 days after 
Dose 2), Day 209 (6 months after Dose 2), and Day 394 for measurement of 

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SARS-CoV-2-specific bAb and nAb responses. Blood samples will also be tested for the 
development of Ab directed against nonvaccine antigen (eg, Ab against the nucleocapsid 
protein), which will signify infection with SARS-CoV-2. The incidence of SARS-CoV-2 
infection among vaccine recipients and placebo recipients will be compared to assess the 
potential for mRNA-1273 to reduce the rate of infection in vaccine recipients. 
Figure 2: 
Study Schema (Part 1A, Blinded Phase) 
Abbreviations: D = day; DSMB = Data Safety Monitoring Board, IA = interim analysis, 
immune = immunogenicity, NP = nasopharyngeal or nasal swab, V = visit, yo = years old. 
Part 1A, the Blinded Phase, comprises 8 scheduled visits including a Screening Visit and 
7 scheduled visits, of which Visit 2 and Visit 4 will be virtual/telephone visits and the other visits 
will be in-clinic visits. 
The study duration will be approximately 14 months, which includes 1 month for Screening 
(Day ˗28 to Day 1), 1 month for dosing (on Day 1 and Day 29), and, for participants who 
received mRNA-1273 in Part 1A, 12 months of follow-up after the second dose to monitor for 
safety, immunogenicity, and efficacy. Participants who received placebo in Part 1A will still be 
in the study for approximately 14 months total but will be followed for approximately 4 months 
following their second dose of mRNA-1273 in Part 1B before receiving a BD. 
Note: Day 0 and Day 1 may be combined on the same day (Table 10). 
After providing informed consent/assent, participants will undergo Screening assessments to 
determine study eligibility. Screening assessments (Table 10) must be completed after signing 
the ICF/assent form. The investigator will review study entry criteria to determine the participant 
eligibility during the Screening Period. 
Eligible participants will enter the Treatment Period. 

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On Day 1, after the completion of the scheduled assessments (Table 10), participants will be 
administered a single IM dose of mRNA-1273 (100 µg) or placebo (procedures will be detailed 
in the mRNA-1273-P203 Pharmacy Manual). Participants will be closely monitored for safety 
and will remain at the study site for observation for at least 30 minutes after dosing. On Day 29, 
the second dose of IP will be administered. Participants will be monitored for 12 months after the 
second dose of IP for safety and immunogenicity assessments. 
To test for the presence of SARS-CoV-2 by RT-PCR, NP or nasal swab samples will be 
collected on each day of injection prior to dosing and on Day 57 (28 days post Dose 2), 
according to the SoA (Table 10). 
During the course of the study, participants who meet prespecified disease criteria that suggest 
possible SARS-CoV-2 infection will be asked to contact the study site to arrange for a prompt, 
thorough, and careful assessment, including an NP or nasal swab sample to be tested for the 
presence of SARS-CoV-2 by RT-PCR. Confirmed, symptomatic cases of SARS-CoV-2 infection 
will be captured as MAAEs and reported in an expedited time frame to the Sponsor 
(Section 7.4.3). 
All participants will be monitored for safety and reactogenicity and provide predose and 
postdose blood specimens for immunogenicity through 12 months after the second dose of 
mRNA-1273. 
Participants will be instructed on the day of the first dose (Day 1) and reminded on the day of the 
second dose (Day 29) how to document and report solicited local or systemic ARs in a provided 
eDiary. Solicited ARs, unsolicited AEs, MAAEs, AEs leading to withdrawal, AESIs, and SAEs 
will be assessed as described in Section 7.1, according to the timepoints in the SoA (Table 10). 
Blood sampling for immunogenicity testing is scheduled throughout the study: on the day of 
injection before the first dose and 1, 6, and 12 months after the second dose. 
Participants may experience AEs that necessitate an unscheduled visit, including situations when 
the investigator asks a participant to return to the study clinic for an unscheduled visit following 
the report of an AE. Additional examinations may be conducted at these visits as necessary to 
ensure the safety and well-being of participants during the study. eCRF should be completed for 
each unscheduled visit. 
3.1.1.2. 
Part 1B, the Open-label Observational Phase  
Part 1B, the Open-label Observational Phase of the study, will be prompted by the authorization 
of a COVID-19 vaccine under an EUA for any persons under the age of 18 years. Participants 
will be transitioned to Part 1B of the study as their age group becomes EUA-eligible. This 
transition permits all ongoing study participants to eventually be informed of the availability and 
eligibility criteria of any COVID-19 vaccine made available under an EUA and the option to 
offer all ongoing study participants an opportunity to schedule a Participant Decision Visit to 
know their original treatment assignment (placebo vs. mRNA-1273 100 µg vaccine). 
Part 1B provides the opportunity for study participants to be informed regarding the EUA, to be 
unblinded to their original assignment (mRNA-1273 or placebo), and, for those who previously 
received placebo, to actively request to receive 2 doses of mRNA-1273 (100 µg) vaccine. 

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Figure 3: 
Study Schema (Part 1B, Open-label Observational Phase) 
 
Abbreviations: BD = booster dose; SoA = Schedule of Assessments. 
At the Participant Decision Clinic Visit (Table 11), EUA-eligible participants will: 
• Be given the option to be unblinded as to their original group assignment (placebo vs. 
mRNA-1273 vaccine [100 µg]), 
• Be counseled about the importance of continuing other public health measures to 
limit the spread of disease including social distancing, wearing a mask, and 
hand-washing, 
• Sign a revised ICF and assent if not signed at a previous clinic visit, and 
• Provide an NP or nasal swab for RT-PCR for SARS-CoV-2 and a blood sample for 
serology and immunogenicity. 
Participants that decline unblinding will remain in Part 1A and follow the Part 1A SoA in 
Table 10. 
After the Participant Decision Clinic Visit, participants that consent to unblinding will follow the 
Part 1A SoA (Table 10) or Part 1B SoA (Table 12) as follows: 
• Participants received placebo in Part 1A and consent to receiving 2 doses of 
mRNA-1273 in Part 1B: These participants will proceed to Part 1B and follow the 
Part 1B SoA in Table 12 until BD is offered. 
• Participants received 2 doses of mRNA-1273 in Part 1A: Due to statistical 
considerations, these participants will be considered in the Open-label Observational 
Phase but will continue to follow the Part 1A SoA in Table 10 until BD is offered. 

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3.1.1.3. 
Part 1C-1, Homologous Booster Phase  
Part 1C-1 Homologous Booster Phase is designed to offer participants in Part 1A and Part 1B, 
who are at least 5 months from the last dose, the option to request a BD (50 µg) of mRNA-1273. 
If eligible, each study participant will receive a notification letter and will be asked to schedule a 
BD-1 Visit at their study site. Principal investigators should consider current local public health 
guidance for administration of COVID-19 vaccines under EUA and marketing authorization (if 
any) when determining the scheduling priority of participants. 
Figure 4: 
Study Schema (Part 1C-1, Open-label Homologous Booster Dose 
Observational Phase) 
 
Abbreviations: BD = booster dose; D = day; SoA = Schedule of Assessments 
At the BD-1 Visit, each participant will: 
• Be encouraged to remain in the ongoing study, 
• Sign a revised ICF that includes both updated safety information relevant to the 
ongoing study and a BD, and the option to receive a BD, 
• Be given the option to receive a BD consisting of a 50 μg dose of mRNA-1273, 
• Be counseled about the importance of continuing other public health measures to 
limit the spread of disease including social distancing, wearing a mask, and hand-
washing. 
At the BD-1 Visit, participants who request a BD and are eligible will have the following study 
site visits and complete scheduled activities (subject to investigational vaccine availability) 
according to the Part 1C-1 Supplemental SoA: 
• BD-1 Visit: Participants will receive a single 50 μg dose of mRNA-1273, 
• BD-1a Visit: All participants who chose to receive BD, Day 4, 3 days after BD on 
Day 1, 
• BD-2 Visit: Day 29, 28 days after the BD on Day 1, 

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• BD-3 Visit: Day 181, 180 days after the BD on Day 1, 
• BD-4 Visit: Day 361, 360 days after the BD on Day 1. 
Participants that crossed over from placebo to mRNA-1273 and decline BD will continue with 
Part 1B SoA (Table 12). 
Participants that received mRNA-1273 in Part 1A and decline BD will continue with in Part 1A 
SoA (Table 10). 
The investigator is responsible for conducting all assessments as specified in the Part 1C-1 
Supplemental SoA, according to the schedule. As this Supplemental SoA is intended to occur in 
addition to the original SoAs being followed by all participants in Part 1A or Part 1B, there is a 
possibility for study visits to overlap (ie, Part 1C-1 BD-Day 1 and study visit in Part 1A or 
Part 1B that coincides with Part 1C-1 BD-Day 1). If visits overlap according to respective visit 
windows, a single visit may be done with the combined study procedures completed once. Any 
participant who consented to receive a BD will follow Part 1C-1 SoA. In case a study visit in 
Part 1A or Part 1B coincides with Part 1C-1 BD-Day1, participants should follow Part 1C SoA. 
Note: Participants enrolled in Part 1C-1 who have received the third (booster) dose in this study 
and would like to receive the bivalent COVID-19 vaccine, can receive it outside of Study P203. 
Participants who receive the updated bivalent COVID-19 vaccine may remain in the P203 study 
after receipt of the nonstudy vaccine. However, sites must report this as concomitant medication. 
3.1.1.4. 
Part 1C-2, Heterologous Booster Phase  
Part 1C-2 – Heterologous Booster Phase is designed to provide a BD (50 µg) of mRNA-1273 to 
eligible participants who completed primary COVID-19 vaccination series with a non-Moderna 
vaccine under EUA (ie, Pfizer, Table 4) and are at least 3 months from the last dose. 
Table 4: 
Non-Moderna COVID-19 Vaccine Available Under Emergency Use 
Authorization  
COVID-19 Vaccine – Primary Series 
Primary Series Number of Doses 
Pfizer-BioNTech 
2 doses 
Abbreviation: COVID-19 = coronavirus disease 2019. 
Principal investigators should consider current local public health guidance for administration of 
COVID-19 vaccines under EUA and marketing authorization (if any) when determining the 
scheduling priority of participants. 
At the BD-0/BD-1 Visit, each participant will: 
• Sign an ICF, 
• Be counseled about the importance of continuing other public health measures to 
limit the spread of disease including social distancing, wearing a mask, and 
hand-washing. 
At the BD-1 Visit, participants will have the following study site visits and complete scheduled 
activities (subject to investigational vaccine availability) according to the Part 1C-2 
Supplemental SoA (Table 14): 

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• BD-1 Visit: Participants will receive a single 50 μg dose of mRNA-1273, 
• BD-1a Visit: Day 4, 3 days after BD on Day 1, 
• BD-2 Visit: Day 29, 28 days after the BD on Day 1, 
• BD-3 Visit: Day 181, 180 days after the BD on Day 1, 
• BD-4 Visit: Day 361, 360 days after the BD on Day 1. 
The investigator is responsible for conducting all assessments as specified in the Part 1C-2 
Supplemental SoA, according to the schedule (Table 14). 
Note: Due to emergence of a more divergent variant of concern (ie, Omicron), Study Part 3 was 
initiated to replace the investigative product mRNA-1273 with a bivalent vaccine mRNA-
1273.222. As a result of this amendment, Part 1C-2 enrollment was discontinued effective 
16 August 2022. Booster dosing in the study was also discontinued and was reflected in Protocol 
Amendment 5. Participants enrolled in Part 1C-2 who have received the third (booster) dose in 
this study and would like to receive the bivalent COVID-19 vaccine, can receive it outside of 
Study P203. Participants who receive the updated bivalent COVID-19 vaccine may remain in the 
P203 study after receipt of the nonstudy vaccine. However, sites must report this as concomitant 
medication. 
3.1.2. 
Part 2 Study Design  
Part 2 is an open-label design. The study will evaluate the safety, reactogenicity, and 
effectiveness of a 50 μg primary series of mRNA-1273 SARS-CoV-2 vaccine in healthy 
adolescents 12 to < 18 years of age. 
The study schema and major study events for Part 2 participants who receive the booster dose is 
illustrated in Figure 5 and the SoA is located in Table 15. The study schema for Part 2 
participants who do not receive the booster dose is illustrated in Figure 6 and the SoA is located 
in Table 16. 
This study in adolescents will monitor all participants for a total of 12 months following Dose 2 
or booster dose (third dose) of vaccine. Safety assessments will include solicited ARs (7 days 
after each injection), unsolicited AEs (28 days after each injection), MAAEs, SAEs, and AESIs 
(including MIS-C) throughout the study period and AEs leading to discontinuation from dosing 
and/or withdrawal from study. 
Blood samples will be collected from all participants at baseline (Day 1) and at specified visits 
presented in Part 2 SoA (Table 15 for participants who receive the booster dose and Table 16 for 
participants who do not receive the booster dose) for measurement of SARS-CoV-2 specific 
binding and nAb responses. Blood samples will also be tested for the development of Ab 
directed against nonvaccine antigen (eg, Ab against the nucleocapsid protein), which will signify 
infection with SARS-CoV-2. Blood sample will be collected 3 days after Dose 2 or booster dose 
for future biomarker analysis (ie, inflammatory and/or cardiac biomarkers). 
The incidence of SARS-CoV-2 infection after mRNA-1273 vaccination will be evaluated. 

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Figure 5: 
Study Schema (Part 2 For Participants Who Receive The Booster Dose) 
 
Abbreviations: D = day; IA = interim analysis; immuno = immunogenicity; V = visit. 
Figure 6: 
Study Schema (Part 2 For Participants Who Do Not Receive The Booster 
Dose) 
 
Abbreviations: D = day; IA = interim analysis; immuno = immunogenicity; SC = safety call; SFU = safety follow-
up; V = visit. 
Part 2 for participants who receive the booster dose comprises 13 scheduled visits including a 
Screening Visit and 12 scheduled visits, of which Visit 2, Visit 5, and Visit 9 will be 
virtual/telephone visits and the other visits will be in-clinic visits. 

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Part 2 for participants who do not receive the booster dose comprises 11 scheduled visits 
including a Screening Visit and 10 scheduled visits, of which Visit 2, Visit 5, and Visit 7 will be 
virtual/telephone visits and the other visits will be in-clinic visits. Participants who receive the 
booster dose of mRNA-1273 in Part 2 will be in the study approximately 17 months, which 
includes 1 week for screening (Day ˗7 to Day 1), 4 months for dosing (on Day 1, Day 29, and 
Day 149), and 12 months of follow-up after the booster dose. Participants who do not receive the 
booster dose of mRNA-1273 in Part 2 will be in the study approximately 12 months, which 
includes 1 week for Screening (Day ˗7 to Day 1), 1 month for dosing (on Day 1 and Day 29), and 
12 months of follow-up after Dose 2. 
This study will be conducted in compliance with the protocol, GCP, and all applicable regulatory 
requirements. 
Note: Due to emergence of a more divergent variant of concern (ie, Omicron), Study Part 3 was 
initiated to replace the investigative product mRNA-1273 with a bivalent vaccine mRNA-
1273.222. This amendment aimed to assess primary series of 50 µg bivalent mRNA-1273.222 in 
Part 3 of the study. As a result of this amendment, Part 2 enrollment was discontinued effective 
16 August 2022. The booster administration (Protocol Amendment 4) was also removed and was 
reflected in the Protocol Amendment 5 SoA. Participants enrolled in Part 2 who have receive the 
primary series or third (booster) dose in this study and would like to receive the bivalent 
COVID-19 vaccine, can receive it outside of Study P203. Participants who receive the updated 
bivalent COVID-19 vaccine may remain in the P203 study after receipt of the nonstudy vaccine. 
However, sites must report this as concomitant medication. 
Part 2 participants enrolled under Protocol Amendment 4 who have already received the booster 
dose will continue the study with the Protocol Amendment 4 Part 2 SoA (Table 15). 
3.1.3. 
Part 3 Study Design  
Part 3 was initially designed as an open-label study to evaluate safety, reactogenicity, and 
effectiveness of a 2-dose 50 µg primary series of mRNA-1273.222 SARS-CoV-2 vaccine 
administered 6 months apart. An interim analysis was conducted which demonstrated robust 
immunogenicity of a single 50 µg mRNA-1273.222 dose. The pre-specified co-primary 
endpoints were also achieved allowing inference of vaccine effectiveness of a single dose of 
mRNA-1273.222 from the pivotal P301 study. Based on these results, the study design was 
amended to primarily evaluate the safety, reactogenicity, and effectiveness of a single dose 50 μg 
primary series of mRNA-1273.222 SARS-CoV-2 vaccine in at least 300 healthy adolescents 
12 to <18 years of age. 
The study schema and major study events for Part 3 participants who receive Dose 2 is illustrated 
in Figure 7 and the SoA is described in Table 17. The study schema for participants who receive 
a single dose is illustrated in Figure 8 and the SoA is described in Table 18. 
Safety follow-up in Part 3 participants who receive 1 dose of vaccine will be 6 months after 
dosing and participants who receive 2 doses will be followed for 1 month following Dose 2. 
Safety assessments will include solicited ARs (7 days after each injection), unsolicited AEs 
(28 days after each injection), MAAEs, SAEs, and AESIs (including MIS-C) throughout the 
study period and AEs leading to discontinuation from dosing and/or withdrawal from study. 

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Blood samples will be collected from all participants at baseline (Day 1) and at visits specified in 
Part 3 SoA (Table 17 for participants who receive Dose 2 and Table 18 for participants who 
receive a single dose) for measurement of SARS-CoV-2 specific bAb and nAb responses up to 
1 month after Dose 2 or 6 months after Dose 1 for participants who receive a single dose. Blood 
samples will also be tested for the development of Ab directed against nonvaccine antigen (eg, 
Ab against the nucleocapsid protein), which will signify infection with SARS-CoV-2. Blood 
samples will be collected 3 days after Dose 1 and 3 days after Dose 2 (Day 184), for future 
biomarker analysis (ie, inflammatory and/or cardiac biomarkers). 
The incidence of SARS-CoV-2 infection after mRNA-1273.222 vaccination will be evaluated. 
Participants who receive 2 doses of mRNA-1273.222 in Part 3 will be in the study for 
approximately 7 months including 1 week for Screening (Day -7 to Day -1), 6 months for dosing 
(Day 1 to Day 181), and 1 month of follow-up after Dose 2. Participants who receive a single 
dose of mRNA-1273.222 in Part 3 will be in the study for approximately 6 months including 
1 week for Screening (Day -7 to Day -1), dosing (Day 1), and 6 months of follow-up after 
dosing. 
Note: Participants who receive the updated COVID-19 vaccine may remain in the P203 study 
after receipt of the nonstudy vaccine. However, sites must report this as concomitant medication. 
Figure 7: 
Study Schema Part 3 (For Participants Who Receive Dose 2) 
 
Abbreviations: D = day; IA = interim analysis; immuno = immunogenicity; M = month; NP = nasopharyngeal; 
SC = safety call; SFU = safety follow-up; V = visit. 

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Figure 8: 
Study Schema Part 3 (For Participants Who Receive a Single Dose) 
 
Abbreviations: D = day; IA = interim analysis; immuno = immunogenicity; M = month; NP = nasopharyngeal; 
SC = safety call; SFU = safety follow-up; V = visit. 
3.2. 
Scientific Rationale for Study Design  
The single age cohort in this Phase 2/3 study, 12 to < 18 years of age, was established to 
understand the tolerability and immunogenicity of 100 µg (Part 1A) and 50 µg (Part 1C-1, 
Part 1C-2, and Part 2) mRNA-1273, as well as 50 µg (Part 3) mRNA-1273.222 in an adolescent 
population. The lower age boundary used in this study is consistent with the definition of 
adolescence provided by the American Academy of Pediatrics (Hardin et al 2017). 
With SARS-CoV-2 expected to be circulating in the general population during the study, all 
participants will provide preinjection blood samples and postinjection blood samples for Ab 
analysis through 12 months after the last dose of IP during Part 1A, Part 2, and through 6 months 
(for participants who receive Dose 2) or 1 to 6 months after the last dose of IP in Part 3 of the 
study. In addition, participants will have NP or nasal swab samples collected before the injection 
on Day 1 (Part 1A, Part 1C, Part 2, and Part 3), Day 29 (Part 1A, Part 2, and Part 3), Day 149 
(Part 2 participants who receive the booster dose), and Day 181 (Part 3 participants who receive 
Dose 2); additional timepoints are in the SoA (Table 10 and Table 12 through Table 18). 
Furthermore, with any signs or symptoms or MAAE suggesting SARS-CoV-2 infection in a 
participant, an additional nasal or NP swab sample and a blood sample will be taken to confirm 
the diagnosis of SARS-CoV-2 via serology and RT-PCR. Additionally, clinical information will 
be carefully collected to evaluate the severity of the clinical case. 

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As it is possible that participants are naturally exposed to SARS-CoV-2 through community 
exposure, the NP or nasal swab samples collected before study injection and the serologic assays 
for Ab responses to nonvaccine antigen(s) may help discriminate between natural infection and 
vaccine-induced Ab responses, should such discrimination be needed. 
Part 1B, is the Open-label Observational Phase. During Part 1B of the study, all ongoing study 
participants were permitted (a) to be informed of the availability and eligibility criteria of any 
COVID-19 vaccine made available under an EUA and (b) to schedule a study visit to know their 
original group assignment (placebo vs. mRNA-1273 vaccine). Part 1B also provided the 
opportunity for eligible study participants who previously received placebo to receive 2 doses of 
mRNA-1273 vaccine under open-label conditions. 
Part 1C, the Booster Phase and Part 2, were prompted by the recent interim results of an ongoing 
Moderna Phase 2 study (mRNA-1273-P201). In Part A of Study mRNA-1273-P201, the time 
course and magnitude of antibody (both bAb and nAb) responses to mRNA-1273 was similar 
between 100 µg and 50 µg dose levels (both showing strong immunogenicity) at each 
postbaseline timepoint (Days 29, 43, 57, and 209), although the 100 µg dose group had 
numerically greater responses. In Part B of Study mRNA-1273-P201 in which participants who 
had received 2 doses of 50 µg or 100 µg of mRNA-1273 6-8 months prior were administered a 
50 µg booster of mRNA-1273, participants demonstrated enhanced immune responses compared 
to preboost levels and met the noninferiority criteria stipulated in the FDA Guidance on EUA for 
Vaccines to Prevent COVID-19. In addition, interim results from Study mRNA-1273-P205 show 
that a 50 µg booster of mRNA-1273 increased nAb levels against Omicron approximately 
37-fold compared to preboost levels. No new safety signals emerged upon administration of the 
BD in Study mRNA-1273-P201. Available data (DMID 21‐0012) also show that heterologous or 
mixed series of COVID-19 vaccine-induced strong immune response in the adult population with 
persons who received an mRNA‐based booster vaccination achieving a four‐fold increase in their 
neutralization response more frequently than those who were boosted with Ad26.COV.S. 
(Atmar et al 2021). 
Part 3 was prompted by preclinical data on bivalent vaccine (mRNA-1273.214 given as 2 dose 
primary series) showing broader neutralization across divergent lineages. Preclinical mice 
studies also show increased immunogenicity after BD of the BA.1 & BA.4/BA.5 Omicron 
Bivalent Vaccines (mRNA-1273.214 & mRNA-1273.222). Further, mRNA-1273.214 when 
given as 50 µg BD in Study P205 participants elicited superior nAb responses against the 
Omicron subvariants BA.4, BA.5 compared with mRNA-1273 50 μg (nominal α of 0.05) and the 
BA.4, BA.5. nAb response was consistently higher in the mRNA-1273.214 group compared to 
the mRNA-1273 group in participants with and without prior SARS-CoV-2 infection (although 
higher GMT titers post BD were observed in those who were SARS-CoV-2 positive at pre-BD). 
Data also demonstrate antibody responses 180 days after the 50 μg mRNA-1273.211 BD were 
higher than those after a 50 μg mRNA-1273 BD (NCT04405076; Chalkias et al 2022a) against 
the ancestral SARS-CoV-2 and Beta, as well as Omicron BA.1 and Delta variants. In addition, 
the bivalent Omicron BA.4/BA.5-containing vaccine mRNA-1273.222 elicited superior 
neutralizing antibody responses against BA.4/BA.5 compared to mRNA-1273, with no safety 
concerns identified (Chalkias et al 2022c). Given the increasing prevalence of SARS-CoV-2 
infection in the community (Clarke et al 2022), effectiveness of 50 µg mRNA-1273.222 post 
dose 1 will be evaluated as a primary objective under Part 3. Recent IA results from Study P203 
Part 2 also support evaluation of immunogenicity of a single 50 µg-dose. Study P203 Part 2 

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interim results show higher immunogenicity post dose 1 of 50 µg mRNA-1273 in Study P203 
unvaccinated baseline SARS-CoV-2 positive adolescent participants when compared to 
immunogenicity post primary series in unvaccinated baseline SARS-CoV-2 negative young 
adults in Study P301 (GMR of 4.322 [95% CI: 3.274, 5.707]). An IA conducted for Part 3 
demonstrate robust immunogenicity of a single 50 µg mRNA-1273.222 dose. The pre-specified 
co-primary endpoints were also met allowing inference of vaccine effectiveness of a single dose 
from the pivotal Study P301. The study vaccine was also well-tolerated after a median of 
~1 month after Dose 1. Based on these results, the second dose of mRNA-1273.222 in Part 3 was 
removed. 
Based on cumulative evidence, the benefit-risk profile of monovalent mRNA-1273 and bivalent 
mRNA-1273.222 vaccine is favorable, particularly in light of increasing breakthrough disease 
with the emergence of the Delta and Omicron variants. 
3.3. 
Justification for Dose, Control Product, and Choice of Study 
Population  
The 100 g dose level is currently being investigated in a large Phase 3 efficacy study in adults 
18 years of age and older; therefore, based on this and the results of the studies described in 
Section 1.2.2, the Sponsor intended to study a single dose level of 100 g in Part 1A of this 
Phase 2/3 study in the adolescents age group of 12 to < 18 years of age. 
At the time of study initiation, there were no licensed SARS-CoV-2 vaccines available, and so 
0.9% sodium chloride was used as a placebo control for the safety and immunogenicity 
assessments. The mRNA-1273 vaccine and placebo injections look different, so administration 
was blinded in Part 1A of this study (Section 8.1). 
Interim data from the current Part 1A Study P203 (based on a data snapshot of 08 May 2021) 
show that the primary immunogenicity objective was met by demonstrating noninferiority of 
both the (i) GM value of serum nAb and (ii) the seroconversion rate from adolescent participants 
compared with those from young adults (aged 18 to 25 years) enrolled in the ongoing Phase 3 
efficacy study (Study P301). 
Following potential EUA of a COVID-19 vaccine for persons under 18 years of age, a study 
amendment was designed to give EUA-eligible participants the opportunity to transition to 
Part 1B, the Open-label Observational Phase (Figure 3). Transitioning the study to Part 1B, 
open-label Observational Phase, permits (a) all ongoing study participants to be informed of the 
availability and eligibility criteria of any COVID-19 vaccine made available under an EUA and 
(b) the option to offer all ongoing study participants who request unblinding an opportunity to 
schedule a study visit to know their original group assignment (placebo vs. mRNA-1273 [100 µg 
vaccine]). Part 1B, the Open-label Observational Phase, also provides the opportunity for study 
participants who previously received placebo to request to receive 2 doses of mRNA-1273 
(100 µg) vaccine. 
For Part 1C (provision for the option of a single 50 µg BD for eligible participants during the 
Open-Label Observational Phase) and for Part 2 (evaluation of 2 doses of 50 µg given 28 days 
apart), the selected 50 µg dose was based primarily on data from Study mRNA-1273-P201. For 
Part 1C-2, participants will be boosted at least 3 months post Dose 2. For Part 1C-1, participants 
are well beyond 3 months post Dose 2 and thus will not be changed to a BD at least 3 months 

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post Dose 2. In Part A of Study mRNA-1273-P201, the time course and magnitude of antibody 
(both bAb and nAb) responses to mRNA-1273 was similar between 100 µg and 50 µg dose 
levels (both showing strong immunogenicity) at each postbaseline timepoint (Days 29, 43, 57, 
and 209), although the 100-µg dose group had numerically greater responses. In Part B of 
Study mRNA-1273-P201, administration of a 50 µg BD of mRNA-1273 6 months or more after 
the primary series, improved the immune responses to 1.7-fold the peak achieved after the 
primary vaccination series in the current mRNA-1273-P301 study, where efficacy of 
mRNA-1273 against COVID-19 was demonstrated. In addition, interim results from 
Study mRNA-1273-P205 show that 50 µg booster of mRNA-1273 increased nAb levels against 
Omicron approximately 37-fold compared to preboost levels. 
Available data also show that heterologous or mixed series of COVID-19 vaccine-induced strong 
immune response in the adult population (Atmar et al 2021). In a recent DMID study 
(DMID 21-0012), interim data show Day 15 post‐boost neutralization titers ranged from 
676.1-901.8 IU50/ml for participants boosted with 100 µg mRNA‐1273 compared to 
31.2-382.2 IU50/ml for those boosted with Ad26.COV2.S, and 341.3‐677.9 IU50/mL for those 
boosted with BNT162b2. In general, Day 15 titers post‐boost were highest in 
mRNA-1273-primed participants, followed by BNT162b2 and Ad26.COV2.S, irrespective of the 
booster vaccine administered (Atmar et al 2021). 
For Part 3, the rationale for assessment of 50 µg primary series of the bivalent Omicron 
containing vaccine mRNA-1273.222 is based on the preclinical data on bivalent vaccines given 
as primary series (mRNA-1273.214) and as BD (mRNA-1273.222) that show robust 
immunogenicity and broader neutralization across divergent lineages. Clinical data from 
mRNA-1273.214 bivalent vaccine (given as a 50 µg BD) also show consistent robust 
immunogenicity, regardless of SARS-CoV-2 infection status in participants (although higher 
GMT titers post BD were observed in those who were SARS-CoV-2 positive at pre-BD), with 
acceptable safety profile. Data also demonstrates antibody responses 180 days after the 50 μg 
mRNA-1273.211 BD were higher than those after a 50 μg mRNA-1273 BD (NCT04405076; 
Chalkias et al 2022a) against the ancestral SARS-CoV-2 and Beta, as well as Omicron BA.1 and 
Delta variants. In addition, the bivalent Omicron BA.4/BA.5-containing vaccine 
mRNA-1273.222 elicited superior neutralizing antibody responses against BA.4/BA.5 compared 
to mRNA-1273, with no safety concerns identified (Chalkias et al 2022c).  
These data together with increasing prevalence of SARS-CoV-2 infection in the community 
(Clarke et al 2022) as well as recent interim results from Study P203 Part 2 showing robust 
immunogenicity after dose 1 of mRNA-1273 in unvaccinated baseline SARS-CoV-2 positive 
adolescent participants, prompted the evaluation of the immunogenicity of 2 doses of the 
bivalent mRNA-1273.222 vaccine given 6 months apart. The 6-month interval will allow 
evaluation of the immunogenicity of Dose 1. An IA conducted for Part 3 demonstrate robust 
immunogenicity of a single 50 µg mRNA-1273.222 dose. The pre-specified co-primary 
endpoints were also met allowing inference of vaccine effectiveness of a single dose from the 
pivotal Study P301. The study vaccine was also well-tolerated after a median of ~1 month after 
Dose 1. Based on these results, the second dose of mRNA-1273.222 in Part 3 was removed. 
Taken together, these data strongly suggest that a monovalent 50 µg mRNA‐1273 given as a 
2 dose primary series, as a homologous and heterologous booster vaccine is anticipated to 
provide strong immunogenicity in the adolescent population. Similarly, these data also suggest 

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that a bivalent 50 µg mRNA‐1273.222, given as 1 dose or 2 doses, may provide strong 
immunogenicity in the adolescent population. 
3.4. 
End-of-Study Definition  
The EoS is defined as the date when the last data are available. A participant is considered to 
have completed the study if the participant has completed all periods of the study including the 
last visit or the last scheduled procedure as shown in the SoAs. 

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4. 
STUDY POPULATION  
Participants will be enrolled at approximately 35 to 64 study sites in the USA or out of USA 
countries. 
Prospective approval of protocol deviations to recruitment and enrollment criteria, also known as 
protocol waivers or exemptions, is not permitted. 
4.1. 
Eligibility Criteria (Part 1A, Part 2, and Part 3)  
4.1.1. 
Inclusion Criteria  
Each participant must meet all of the following criteria at the Screening Visit (Day 0) or at 
Day 1, unless noted otherwise, to be enrolled in this study: 
1. Male or female, 12 to < 18 years of age at the time of consent (Screening Visit, Day 0) 
who, in the opinion of the investigator, is in good general health based on review of 
medical history and Screening physical examination. 
2. Investigator assessment that the participant, in the case of an emancipated minor, or 
parent(s)/LAR(s) understand and are willing and physically able to comply with 
protocol-mandated follow-up, including all procedures and provides written informed 
consent/assent. 
3. BMI at or above the third percentile according to WHO Child Growth Standards at the 
Screening Visit (Day 0); see Section 10.2.18. 
4. Female participants of nonchildbearing potential may be enrolled in the study. 
Nonchildbearing potential is defined as premenarche or surgically sterile (history of 
bilateral tubal ligation, bilateral oophorectomy, hysterectomy). 
5. Female participants of childbearing potential may be enrolled in the study if the 
participant fulfills all the following criteria: 
• Has a negative pregnancy test at Screening (Day 0), on the day of the first injection 
(Day 1), and on the day of the second injection (Day 29 in Part 1A and Part 2, and 
Day 181 in Part 3). 
• Has practiced adequate contraception or has abstained from all activities that could 
result in pregnancy for at least 28 days prior to the first injection (Day 1). 
6. Has agreed to continue adequate contraception or abstinence through 3 months following 
the second injection (Day 29 in Part 1 A and Part 2, and Day 181 in Part 3). 
Adequate female contraception is defined as consistent and correct use of approved contraceptive 
method in accordance with the product label (Section 10.3). 
4.1.2. 
Exclusion Criteria  
Participants who meet any of the following criteria at the Screening Visit (Day 0) or at Day 1, 
unless noted otherwise, will be excluded from the study: 
1. Has a known history of SARS-CoV-2 infection within 2 weeks prior to administration of 
IP or known close contact with anyone with laboratory-confirmed SARS-CoV-2 infection 

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or COVID-19 within 2 weeks prior to administration of IP (Part 2 participants only). For 
Part 3 participants, known history of SARS-CoV-2 infection within 90 days prior to 
administration of IP or known close contact with anyone with laboratory-confirmed 
SARS-CoV-2 infection or COVID-19 within 90 days prior to administration of IP. 
2. Travel outside of the USA or home country (Part 2 and Part 3 only) in the 28 days prior 
to the Screening Visit (Day 0). 
3. Pregnant or breastfeeding. 
4. Is acutely ill or febrile 24 hours prior to or at the Screening Visit (Day 0). Fever is 
defined as a body temperature ≥ 38.0°C/≥ 100.4°F. Participants who meet this criterion 
may have visits rescheduled within the relevant study visit windows. Afebrile participants 
with minor illnesses can be enrolled at the discretion of the investigator. 
5. Prior administration of an investigational CoV (eg, SARS-CoV-2, SARS-CoV, 
MERS-CoV) vaccine. 
6. Current treatment with investigational agents for prophylaxis against COVID-19. 
7. Has a medical, psychiatric, or occupational condition that may pose additional risk as a 
result of participation, or that could interfere with safety assessments or interpretation of 
results according to the investigator’s judgment. 
8. Current use of any inhaled substance (eg, tobacco or cannabis smoke, nicotine vapors). 
9. History of chronic smoking (≥ 1 cigarette a day) within 1 year of the Screening Visit 
(Day 0). 
10. History of illegal substance use or alcohol abuse within the past 2 years. This exclusion 
does not apply to historical cannabis use that was formerly illegal in the participant’s 
state but is legal at the time of Screening. 
11. History of a diagnosis or condition that, in the judgment of the investigator, may affect 
study endpoint assessment or compromise participant safety, specifically: 
• Congenital or acquired immunodeficiency, including HIV infection 
• Suspected active hepatitis 
• Has a bleeding disorder that is considered a contraindication to IM injection or 
phlebotomy 
• Dermatologic conditions that could affect local solicited AR assessments 
• History of anaphylaxis, urticaria, or other significant AR requiring medical 
intervention after receipt of a vaccine 
• Diagnosis of malignancy within the previous 10 years (excluding nonmelanoma skin 
cancer) 
• Febrile seizures 

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12. Receipt of: 
• Any licensed vaccine within 28 days before the first dose of IP or plans for receipt of 
any licensed vaccine within 28 days before and/or after each dose of IP. 
• Systemic immunosuppressants or immune-modifying drugs for > 14 days in total 
within 6 months prior to the day of enrollment (for corticosteroids, ≥ 20 mg/day 
prednisone equivalent). Topical tacrolimus is allowed if not used within 14 days prior 
to the day of enrollment. Participants may have visits rescheduled for enrollment if 
they no longer meet this criterion within the Screening Visit window. Inhaled, nasal, 
and topical steroids are allowed. 
• Intravenous blood products (red cells, platelets, immunoglobulins) within 3 months 
prior to enrollment. 
13. Has donated ≥450 mL of blood products within 28 days prior to the Screening Visit 
(Day 0) or plans to donate blood products during the study. 
14. Participated in an interventional clinical study within 28 days prior to the Screening Visit 
(Day 0) or plans to do so while participating in this study. 
15. Is an immediate family member or has a household contact who is an employee of the 
research center or otherwise involved with the conduct of the study. 
4.2. 
Study Eligibility Criteria (Part 1B)  
1. Participants must have been previously enrolled in the mRNA-1273-P203 study. 
2. Female participants of childbearing potential may be enrolled in the study if the 
participant has a negative pregnancy test on the day of the first injection (OL-Day 1) and 
on the day of the second injection (OL-Day 29). 
4.3. 
Study Eligibility Criteria (Part 1C-1 – Homologous Booster Phase)  
Inclusion Criteria: 
1. Participants must have been previously enrolled in the mRNA-1273-P203 study, are 
actively participating in Part 1A or Part 1B and are least 5 months from the last dose. 
2. Female participants of childbearing potential may be enrolled in the study if the 
participant has a negative pregnancy test on the day of the first injection (BD-Day 1). 
Exclusion Criteria: 
1. Pregnant or breastfeeding. 
2. Is acutely ill or febrile 24 hours prior to or at the Screening Visit (Day 0). Fever is 
defined as a body temperature ≥38.0°C/≥100.4°F. Participants who meet this criterion 
may have visits rescheduled within the relevant study visit windows. Afebrile participants 
with minor illnesses can be enrolled at the discretion of the investigator. 
3. Has a medical, psychiatric, or occupational condition that may pose additional risk as a 
result of participation, or that could interfere with safety assessments or interpretation of 
results according to the investigator’s judgment. 

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4. History of a diagnosis or condition (after enrollment in Part 1A) that, in the judgment of 
the investigator, may affect study endpoint assessment or compromise participant safety: 
• Suspected active hepatitis 
• Has a bleeding disorder that is considered a contraindication to IM injection or 
phlebotomy 
• Dermatologic conditions that could affect local solicited AR assessments 
• History of anaphylaxis, urticaria, or other significant AR requiring medical 
intervention after receipt of a vaccine 
• Diagnosis of malignancy (excluding nonmelanoma skin cancer) 
5. Receipt of: 
• Any authorized or licensed vaccine within 28 days before the first dose of IP or plans 
for receipt of any licensed vaccine through 28 days following the last dose of IP 
(authorized/approved bivalent vaccine against SARS-CoV-2 as 4th BD is not 
exclusionary); OR 
• Any seasonal influenza vaccine within 14 days before the first dose of IP or plans for 
receipt of any seasonal influenza vaccine 14 days following the last dose of IP. 
6. Participated in an interventional clinical study, other than mRNA-1273-P203, within 
28 days prior to the Screening Visit (Day 0) or plans to do so while participating in this 
study. 
4.4. 
Study Eligibility Criteria (Part 1C-2 – Heterologous Booster Dose):  
Inclusion Criteria: 
1. Male or female, 12 to < 18 years of age at the time of consent who, in the opinion of the 
investigator, is in good general health based on review of medical history and Screening 
physical examination AND has completed non-Moderna primary COVID-19 vaccination 
series under EUA (ie, Pfizer) at least 3 months from consent. 
2. Investigator assessment that the participant, in the case of an emancipated minor, or 
parent(s)/LAR understand and are willing and physically able to comply with 
protocol-mandated follow-up, including all procedures and provides written informed 
consent/assent. 
3. BMI at or above the third percentile according to WHO Child Growth Standards at the 
Screening Visit (BD-Day 0). 
4. Female participants of nonchildbearing potential may be enrolled in the study. 
Nonchildbearing potential is defined as premenarche or surgically sterile (history of 
bilateral tubal ligation, bilateral oophorectomy, hysterectomy). Female participants of 
childbearing potential may be enrolled in the study if the participant has a negative 
pregnancy test on the day of the first injection (BD-Day 1) and has agreed to continue 
adequate contraception or abstinence through 3 months following BD (BD-Day 1). 

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Exclusion Criteria: 
1. Has a known history of SARS-CoV-2 infection within 2 weeks prior to administration of 
IP or known close contact with anyone with laboratory-confirmed SARS-CoV-2 infection 
or COVID-19 within 2 weeks prior to administration of IP. 
2. Pregnant or breastfeeding. 
3. Is acutely ill or febrile 24 hours prior to or at the Screening Visit (BD-Day 0). Fever is 
defined as a body temperature ≥38.0°C/≥100.4°F. Participants who meet this criterion 
may have visits rescheduled within the relevant study visit windows. Afebrile participants 
with minor illnesses can be enrolled at the discretion of the investigator. 
4. Has a medical, psychiatric, or occupational condition that may pose additional risk as a 
result of participation, or that could interfere with safety assessments or interpretation of 
results according to the investigator’s judgment. 
5. History of a diagnosis or condition that, in the judgment of the investigator, may affect 
study endpoint assessment or compromise participant safety: 
• Suspected active hepatitis 
• Has a bleeding disorder that is considered a contraindication to IM injection or 
phlebotomy 
• Dermatologic conditions that could affect local solicited AR assessments 
• History of anaphylaxis, urticaria, or other significant AR requiring medical 
intervention after receipt of a vaccine 
• Diagnosis of malignancy (excluding nonmelanoma skin cancer) 
6. Receipt of: 
• Any authorized or licensed vaccine within 28 days before the first dose of IP 
(monovalent COVID-19 primary series vaccines are not exclusionary) or plans for 
receipt of any licensed vaccine through 28 days following the last dose of IP 
(monovalent COVID-19 primary series vaccines as well as authorized/approved 
bivalent vaccine against SARS-CoV-2 as 4th booster are not exclusionary) or any 
seasonal influenza vaccine within 14 days before the first dose of IP or plans for 
receipt of any seasonal influenza vaccine 14 days following the last dose of IP. 
7. Participated in an interventional clinical study, other than mRNA-1273-P203 study, 
within 28 days prior to the Screening Visit (BD-Day 0) or plans to do so while 
participating in this study. 
4.5. 
Lifestyle Restrictions  
Participants must not eat or drink anything hot or cold within 10 minutes before oral temperature 
is taken. 

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4.6. 
Screen Failures (Part 1A: Blinded Phase, Part 2, and Part 3)  
Screen failures are defined as participants who consent to participate in the clinical study but are 
not subsequently randomly assigned to treatment. A minimum set of screen failure information is 
required to ensure transparent reporting of screen failures to meet the CONSORT publishing 
requirements and to respond to queries from regulatory authorities. Minimum information 
includes date of informed consent, demography, reason(s) for screen failure, eligibility criteria, 
and information on any SAE that may have occurred from Day 1 to the time of withdrawal. 

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5. 
STUDY TREATMENT  
5.1. 
Investigational Product Administered  
The term IP refers to mRNA-1273 (100 g for Part 1A and Part 1B, and 50 µg for Part 1C, and 
Part 2), and 50 µg mRNA-1273.222 (Part 3) vaccine or placebo (0.9% sodium chloride) in this 
study. 
The mRNA-1273 is an LNP dispersion of an mRNA encoding the prefusion stabilized S protein 
of SARS-CoV-2 formulated in LNPs composed of 4 lipids (1 proprietary and 3 commercially 
available): the proprietary ionizable lipid SM-102; cholesterol; 1,2-distearoyl-sn-glycero-
3-phosphocholine (DSPC); and 1-monomethoxypolyethyleneglycol-2,3-dimyristylglycerol with 
polyethylene glycol of average molecular weight 2000 (1-monomethoxypolyethyleneglycol-2,3-
dimyristylglycerol polyethylene glycol 2000 [PEG2000-DMG]). 
mRNA-1273 injection is provided as a sterile liquid for injection, white to off-white dispersion 
in appearance, at a concentration of 0.5 mg/mL in 20 mM Tris buffer containing 87 mg/mL 
sucrose and 10.7 mM sodium acetate at pH 7.5. 
The Sponsor initiated the development of modified COVID-19 vaccine leveraging the 
mRNA/LNP technology platform against SARS-CoV-2 variant, which incorporates key 
mutations present in Omicron subvariants BA.4/BA.5. The vaccine IP, mRNA-1273.222, 
contains 2 mRNAs: CX-024414 encoding for the S-2P of Wuhan-Hu-1 and CX-034476 
encoding for the S-2P of Omicron subvariants BA.4/BA.5. 
mRNA-1273.222 will be provided as a sterile solution for injection at a concentration of 
0.1 mg/mL in 20 mM Tris buffer with sucrose, at pH 7.5. The solution will be kept in 2R USP 
Type I borosilicate glass vials with PLASCAP vial seal containing a 13 mm FluroTec-coated 
plug stopper with a 0.8 mL nominal fill volume. For Part 3, each injection preparation will have 
a volume of 0.5 mL and contain 50 µg mRNA-1273.222. 
5.2. 
Randomization (Part 1A Only)  
Random assignment of participants will use a centralized interactive response technology, in 
accordance with pregenerated randomization schedules. 
5.3. 
Dosing and Management of mRNA-1273 Vaccine  
5.3.1. 
Preparation of Study Vaccine for Injection  
Each dose of IP will be prepared for each participant based on the assigned treatment, as detailed 
in the mRNA-1273-P203 Pharmacy Manual. For Part 1A and Part 1B, the volume of IP injected 
will be 0.5 mL consisting of either 100 µg dose of mRNA-1273 or placebo (normal saline), as 
detailed in the mRNA-1273-P203 Pharmacy Manual. For Part 1C and Part 2, each injection will 
have a volume of 0.25 mL and contain mRNA-1273 50 µg. 
For Part 3, each dose of IP will be prepared for each participant as detailed in the 
mRNA-1273-P203 Pharmacy Manual. The volume of IP injected will be 0.5 mL and contain 
50 µg mRNA-1273.222. 

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5.3.2. 
Administration of Study Vaccine  
In the Blinded Phase, Part 1A of the study, each participant will receive 2 doses of IP by IM 
injection, 28 days apart (ie, Day 1 and Day 29) into the deltoid muscle, according to their 
assigned regimen and according to the procedures specified in the mRNA-1273-P203 Pharmacy 
Manual. Preferably, both doses should be administered into the nondominant arm. 
In the open-label Part 1B of the study, mRNA-1273 vaccine will be administered as an IM 
injection into the deltoid muscle following the injection schedule for each group based on the 
product received in Part 1A. Participants who received placebo in Part 1A will receive 2 doses of 
mRNA-1273 (100 µg) on OL – Day 1 and OL-Day 29 of Part 1B (Table 12). Preferably, both 
doses should be administered into the nondominant arm. 
For Part 1C, mRNA-1273 vaccine will be administered as an IM injection into the deltoid 
muscle. Preferably, the dose should be administered into the nondominant arm. Each injection 
will have a volume of 0.25 mL and contain mRNA-1273 50 µg. 
For Part 2, each participant will receive 2 doses of 50 µg mRNA-1273 by IM injection, 28 days 
apart (ie, Day 1, Day 29) into the deltoid muscle, according to the procedures specified in the 
mRNA-1273-P203 Pharmacy Manual. Preferably, all doses should be administered into the 
nondominant arm. 
For Part 3 Protocol Amendment 5, each participant will receive 2 doses of 50 µg mRNA-
1273.222 by IM injection, 6 months apart (ie, Day 1, Day 181). Protocol Amendment 7 was 
implemented to remove the second dose administration; thus, some participants will only receive 
1 dose of mRNA-1273.222. The mRNA-1273.222 will be administered into the deltoid muscle, 
according to the procedures specified in the mRNA-1273-P203 Pharmacy Manual. Preferably, 
all doses should be administered into the nondominant arm. 
At each visit when IP is administered, participants will be monitored for a minimum of 
30 minutes after administration. Assessments will include vital sign measurements and 
monitoring for local or systemic reactions (Table 10, Table 12, Table 13, Table 14, Table 15, 
Table 16, Table 17, and Table 18). 
Eligibility for a subsequent dose of IP will be determined by following the criteria outlined in 
Section 6. 
The study sites will be appropriately staffed with individuals with basic cardiopulmonary 
resuscitation training/certification. Either on-site resuscitation equipment and personnel or 
appropriate protocols for the rapid transport of participant to a resuscitation area or facility are 
required. 
5.3.3. 
Study Vaccine Delivery and Receipt  
The Sponsor or designee is responsible for the following: 
• Supplying the IP 
• Confirming the appropriate labeling of the IP, so that it complies with the legal 
requirements of the USA 

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The investigator is responsible for acknowledging the receipt of the IP by a designated staff 
member at the study site, including the following: 
• Confirming that the IP was received in good condition 
• Confirming that the temperature during shipment from the Sponsor to the 
investigator’s designated storage location was appropriate 
• Confirming that the Sponsor has authorized the IP for use 
• Ensuring the appropriate dose level of IP is properly prepared using aseptic technique 
Further description of the IP and instructions for the receipt, storage, preparation, administration, 
accountability, and destruction of the IP are described in the mRNA-1273-P203 Pharmacy 
Manual. 
5.3.4. 
Study Vaccine Packaging and Labeling  
The Sponsor will provide the investigator (via the study site pharmacy) with adequate quantities 
of IP. The sterile IP is packaged in 10R glass vials with a 5.0-mL fill volume (Part 1A, Part 1B, 
and Part 1C), a 10R glass vial with an 8.0 mL fill volume (Part 1C and Part 2 only), or a 10R 
glass vial with a 6.3 mL fill volume (Part 1C and Part 2 only). The IP will have all required 
labeling per regulations and will be supplied to the pharmacy in an unblinded manner. For Part 3, 
the IP will be packaged in a 2R glass vial. 
The IP will be packaged and labeled in accordance with the standard operating procedures of the 
Sponsor or of its designee, CFR Title 21, ICH GCP guidelines, guidelines for Quality System 
Regulations, and applicable regulations. 
5.3.5. 
Study Vaccine Storage  
The IP must be stored as per the temperature conditions printed on the IP label in a secure area 
with limited access and protected from moisture and light until it is prepared for administration 
(Section 5.3.1). The refrigerator and/or freezer utilized for IP storage should have automated 
temperature recording and a 24-hour alert system in place that allows for rapid response in case 
of refrigerator malfunction. There must be an available backup refrigerator and freezer. The 
refrigerators and freezers must be connected to a backup generator(s). In addition, IP 
accountability study staff are required to keep a temperature log to establish a record of 
compliance with these storage conditions. The study site is responsible for reporting any IP that 
was not temperature controlled during shipment or during storage. Such IP will be retained for 
inspection by the monitor and disposed of according to approved methods. 
5.3.6. 
Study Vaccine Accountability  
It is the investigator’s responsibility that the IP accountability study staff maintain accurate 
records in an IP accountability log of receipt of all IP, study site IP inventory, IP dispensing, IP 
injections, and return to the Sponsor or alternative disposition of used and unused IP vials. 
A study site monitor will review the inventory and accountability log during study site visits and 
at the completion of the study. Additional details are found in the mRNA-1273-P203 Pharmacy 
Manual. 

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5.3.7. 
Study Vaccine Handling and Disposal  
A study site monitor will reconcile the IP inventory during the conduct and at the end of the 
study for compliance. Once fully reconciled at the study site at the end of the study, the IP can be 
destroyed at the investigational site or at a Sponsor-selected third party, as appropriate. 
Vaccine may be destroyed at the study site only if permitted by local regulations and authorized 
by the Sponsor. A certificate of destruction must be completed and sent to the Sponsor or 
designee. 
5.4. 
Study Treatment Compliance  
All doses of IP will be administered at the study site under direct observation of medically 
qualified study staff and appropriately recorded (date and time) in the eCRF. Qualified study site 
staff will confirm that the participant has received the entire dose of IP. If a participant does not 
receive IP or does not receive all of the planned dose, the reason for the missed dose will be 
recorded. Data will be reconciled with study site accountability records to assess compliance. 
Participants who miss the second or third dose due to noncompliance with the visit schedule and 
not due to a safety pause will still be required to follow the original visit and testing schedule as 
described in the protocol and their regimen schedule. Unless consent is withdrawn, a participant 
who withdraws or is withheld from receiving the second dose will remain in the study and 
complete all safety and immunogenicity assessments required through the participant’s last 
scheduled study visit. 
The study site staff are responsible for ensuring that participants comply with the allowed study 
visit windows. If a participant misses a visit, every effort should be made to contact the 
participant and complete a visit within the defined visit window (Part 1A, Table 10; Part 1B, 
Table 12; Part 1C, Table 13 and Table 14; Part 2, Table 15 for participants who receive the 
booster dose and Table 16 for participants who do not receive the booster dose; and Part 3, 
Table 17 for participants who receive Dose 2 and Table 18 for participants who receive a single 
dose. If a participant does not complete a visit within the time window, that visit will be 
classified as a missed visit and the participant will continue with subsequent scheduled study 
visits. All safety requirements of the missed visit will be captured and included in the subsequent 
visit. 
5.5. 
Prior and Concomitant Medications  
5.5.1. 
Prior Medications and Therapies  
Information about prior medications (including any prescription or over-the-counter medications, 
vaccines, or blood products) taken by the participant within the 28 days before providing 
informed consent/assent (or as designated in the inclusion/exclusion requirements) will be 
recorded in the participant’s eCRF. 
5.5.2. 
Concomitant Medications and Therapies  
At each study visit, study site staff must question the participant and/or the participants’ 
parent(s)/LAR(s) regarding any medications taken and vaccinations received by the participant 
and record the following information in the eCRF: 

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• All nonstudy vaccinations administered within the period starting 28 days before the 
first dose of IP. 
• All concomitant medications and nonstudy vaccinations taken through 28 days after 
each dose of IP (Part 1A) or throughout the study (Part 1B, Part 1C-1, Part 1C-2, Part 
2, and Part 3). Antipyretics and analgesics taken prophylactically (ie, taken in the 
absence of any symptoms in anticipation of an injection reaction) will be recorded as 
such. 
• Any concomitant medications relevant to or for the treatment of an SAE or a MAAE. 
• Participants will be asked in the eDiary if they have taken any antipyretic or analgesic 
to treat or prevent fever or pain within 7 days after each dose of IP, including the day 
of injection. Reported antipyretic or analgesic medications should be recorded in the 
source document by the study site staff during the postinjection study visits or via 
other participant interactions (eg, telephone calls). 
5.5.3. 
Recording of Concomitant Medications and Concomitant Vaccinations  
Study site staff must question the participant regarding any medications taken and vaccinations 
received by the participant and record the following information in the eCRF: 
• All nonstudy vaccinations administered within the period starting 28 days before the 
first dose of IP. 
• Seasonal influenza vaccine administered for the current influenza season (typically 
October through April in the Northern Hemisphere). 
• All concomitant medications and nonstudy vaccinations taken through 28 days after 
each dose of IP (Part 1A) or throughout the study (Part 1B, Part 1C-1, Part 1C-2, Part 
2, and Part 3). Antipyretics and analgesics taken prophylactically (ie, taken in the 
absence of any symptoms in anticipation of an injection reaction) will be recorded as 
such. 
• Any concomitant medications used to prevent or treat COVID-19 or its symptoms. 
• Any concomitant medications relevant to or for the treatment of an SAE or a MAAE. 
• Participants will be asked in the eDiary if they have taken any antipyretic or analgesic 
to treat or prevent fever or pain within 7 days after each IP dose, including on the day 
of dosing. Reported antipyretic or analgesic medications should be recorded in the 
source document by the study site staff during the postinjection study visits or via 
other participant interactions (eg, phone calls). 
Concomitant medications (including vaccinations) will be coded using the WHO Drug 
Dictionary. If a participant takes a prohibited drug therapy, the investigator and the CRO’s 
medical monitor will make a joint decision about continuing or withholding further injection of 
the participant based on the time the medication was administered, the drug’s pharmacology and 
pharmacokinetics, and whether use of the medication will compromise the participant’s safety or 
interpretation of the data. It is the investigator’s responsibility to ensure that details regarding the 
concomitant medications are adequately recorded in the eCRF. 

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5.5.4. 
Concomitant Medications and Vaccines that May Lead to the Elimination of a 
Participant from Per-Protocol Analyses  
The use of the following concomitant medications and/or vaccines will not require withdrawal of 
the participant from the study (with the exception of planned or actual receipt of a nonstudy 
COVID-19 vaccine either under EUA or licensed for Part 1A and 1B only) but may determine a 
participant’s eligibility to receive a second dose or evaluability in the PP analysis (analysis sets 
are described in Section 8.4: 
• Any investigational or nonregistered product (drug or vaccine) other than the IP used 
during the study period. 
• Immunosuppressants or other immune-modifying drugs administered chronically (ie, 
more than 14 days in total) during the study period. For corticosteroids, this will mean 
that prednisone ≥20 mg/day or the equivalent is not permitted. Inhaled, nasal, and 
topical steroids are allowed. 
• Long-acting immune-modifying drugs administered at any time during the study 
period (eg, infliximab). 
• Immunoglobulins and/or any blood products administered during the study period. 
5.6. 
Intervention After the End of the Study  
Any SAE occurring after the end of the study and considered to be caused by the IP must be 
reported to the Sponsor. 

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6. 
DELAYING OR DISCONTINUING STUDY TREATMENT AND 
PARTICIPANT WITHDRAWAL FROM THE STUDY  
6.1. 
Criteria for Delay of Vaccine Administration  
6.1.1. 
Individual Participant Criteria for Delay of Study Vaccination  
Body temperature (oral) must be measured on dosing visits before vaccine administration. The 
following events constitute criteria for delay of injection, and if either of these events occur at 
the time scheduled for dosing, the participant may receive the study injection at a later date 
within the time window specified in the relevant SoA (Table 10, Table 12, Table 13, Table 14, 
Table 15, Table 16, Table 17, and Table 18), or the participant may be discontinued from dosing 
at the discretion of the investigator (Section 6.2): 
• Acute moderate or severe infection with or without fever at the time of dosing 
• Fever, defined as body temperature ≥38.0°C/≥100.4°F at the time of dosing 
Participants with a minor illness without fever, as assessed by the investigator, can be 
vaccinated. Participants with a fever of ≥38.0°C/≥100.4°F will be contacted within the time 
window acceptable for participation and re-evaluated for eligibility. If the investigator 
determines that the participant’s health on the day of dosing temporarily precludes injection, the 
visit should be rescheduled within the allowed interval for that visit if possible or at a time the 
participant is clinically stable according to the judgment of the investigator. 
If a participant takes a prohibited drug therapy, an injection could be delayed within the visit 
window based on the joint decision of the investigator and the CRO’s medical monitor 
(Section 5.5.3). 
6.2. 
Discontinuing Study Vaccination  
Participants can discontinue study injection (ie, refuse the second dose) for any reason, without 
prejudice to further treatment the participant may need to receive. 
The investigator, in consultation with the Sponsor’s medical monitor, may withhold a participant 
from further injection if the participant experiences any of the following: 
• Becomes pregnant 
• Withdrawal of consent (not related to COVID-19) 
• Develops, during the course of the study, symptoms or conditions listed in the 
exclusion criteria (Section 4.1.2) 
• Experiences an AE (other than reactogenicity) after injection that is considered by the 
investigator to be related to IP (Section 7.5.9) and is of Grade 3 (severe) or greater 
severity 
• Experiences an AE or SAE that, in the judgment of the investigator, requires IP 
withdrawal due to its nature, severity, or required treatment, regardless of the causal 
relationship to vaccine 
• Experiences an AESI 

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• Experiences a clinically significant change in vital sign measurements, or general 
condition that, in the judgment of the investigator, requires vaccine withdrawal 
• Experiences anaphylaxis clearly related to IP 
• Experiences generalized urticaria related to IP 
The reason(s) for withdrawal from further injection will be recorded in the eCRF. 
If a participant takes a prohibited drug therapy, the investigator could withhold the second or 
third dose based on a joint decision of the investigator and the CRO’s medical monitor 
(Section 5.5.3). 
Every reasonable attempt will be made to follow-up with participants for safety throughout the 
entire scheduled study period according to their regimen, even if the participant does not receive 
the second dose or misses one or more visits. Unless participants withdraw consent, they are 
expected to remain in the study and complete all scheduled visits and assessments. 
6.3. 
Participant Discontinuation/Withdrawal from the Study  
Participants who withdraw or are withdrawn from the study will not be replaced. A “withdrawal” 
from the study refers to a situation wherein a participant does not return for the final visit 
planned in the protocol. The statistical management of participant withdrawals is discussed in 
Section 8. 
Participants can withdraw consent and withdraw from the study at any time, for any reason, 
without prejudice to further treatment the participant may need to receive. The investigator will 
request that the participant complete all study procedures pending at the time of withdrawal. 
If participant desires to withdraw from the study because of an AE, the investigator will try to 
obtain agreement to follow-up with the participant until the event is considered resolved or stable 
and will then complete the EOS eCRF. 
Information related to the withdrawal will be documented in the eCRF. The investigator will 
document whether the decision to withdraw a participant from the study was made by the 
participant or by the investigator, as well as which of the following possible reasons was 
responsible for withdrawal: 
• AE (specify) 
• SAE (specify) 
• Death 
• Lost to follow-up 
• Physician decision (specify) 
• Pregnancy 
• Protocol deviation 
• Study terminated by Sponsor 
• Withdrawal of consent by participant (specify) 
• Other (specify) 

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Participants who are withdrawn from the study because of AEs (including SAEs) must be clearly 
distinguished from participants who are withdrawn for other reasons. Investigators will follow-
up with participants who are withdrawn from the study as result of an SAE or AE until resolution 
of the event. 
A participant who withdraws from the study may request destruction of any samples taken and 
not tested, and the investigator must document this in the study site study records. 
If the participant withdraws consent for disclosure of future information, the Sponsor may retain 
and continue to use any data collected before such a withdrawal of consent (Section 10.2.10). 
The Sponsor will continue to retain and use all research data that have already been collected for 
the study evaluation, unless the participant has requested destruction of these samples. All 
biological samples that have already been collected may be retained and analyzed at a later date 
(or as permitted by local regulations). 
6.4. 
Study Pause Rules  
During Part 1A of the study, the investigators, study medical monitor, and Sponsor will monitor 
for events that could trigger a study pause. Study pause rule criteria, events, and thresholds are 
described in Table 5. Although these pause rules are not applicable during Part 1B or Part 1C, 
Part 2, or Part 3, participants will continue to be monitored for the events in Table 5, and the 
Sponsor will be notified if any of these events occur. 
Table 5: 
Pause Rule Criteria, Events, and Thresholds  
Pause Rule 
Criterion 
Event 
Participant Threshold for 
Triggering Study Pause 
1 
Any death due to SARS-CoV-2 infection 
≥ 1 
2 
Any related SAE or related Grade 4 AE 
≥ 1 
3 
Hospitalization due to SARS-CoV-2 infection 
≥ 1 
4a 
Any Grade 3 or higher solicited local AR lasting 
≥ 24 hours and occurring within 7-days of injection 
(Days 1-8) 
≥30 participants out of the first 
300 participants enrolled 
5a 
Any Grade 3 or higher solicited systemic AR lasting 
≥ 24 hours and occurring within 7-days of injection 
(Days 1-8) 
≥30 participants out of the first 
300 participants enrolled 
6a 
Any ≥ Grade 3 or higher unsolicited AR that cannot 
be reasonably attributed to a cause other than 
vaccination 
≥30 participants out of the first 
300 participants enrolled 
Abbreviations: AE = adverse event; AR = adverse reaction; ICU = intensive care unit; SAE = serious adverse event; 
SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2. 
a. 
Pause Rules 4, 5, and 6 apply only to the first 300 participants enrolled. 
If any of the thresholds for a study pause is met during Part 1A, the Sponsor will immediately 
suspend further enrollment, pause study dosing, and notify all investigators. Such a suspension 
will remain in force until the threshold event(s) is (are) reviewed by the DSMB and a 
recommendation to continue is provided to the Sponsor. 

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The investigator or designee is responsible for reporting to the Sponsor, via the EDC system 
within 24 hours of observation, each event that potentially meets any pause rule criterion. The 
Sponsor will inform the DSMB of any event that potentially meets any pause rule criterion. The 
DSMB will review all available study data to adjudicate such events in accordance with the 
DSMB charter. 
The Sponsor will notify the CBER within 48 hours in the event of a study pause. In the event of 
a study pause, all safety and immunogenicity assessments will continue PP. The window 
allowance for injection visits may be extended by an additional 7 days (ie, +14 days) for affected 
participants at the discretion of the Sponsor. 
During Part 1B, Part 1C, Part 2, and Part 3 of the study, the Sponsor will continue to inform the 
DSMB of the occurrence of any of the events in Table 5. The DSMB will review all available 
relevant study data to adjudicate such events in accordance with the DSMB charter. 
6.5. 
Lost to Follow-up  
A participant will be considered LTFU if he or she repeatedly fails to return for scheduled visits 
without stating an intention to withdraw consent and is unable to be contacted by the study site. 
The following actions must be taken if a participant fails to return to the clinic for a required 
study visit: 
• The study site staff must attempt to contact the participant and reschedule the missed 
visit as soon as possible, counsel the participant on the importance of maintaining the 
assigned visit schedule and ascertain whether the participant wishes to and/or should 
continue in the study. 
• Before a participant is deemed LTFU, the investigator or designee must make every 
effort to regain contact with the participant (where possible, 3 telephone calls and, if 
necessary, a certified letter to the participant’s last known mailing address or local 
equivalent methods). These contact attempts (eg, dates of telephone calls and 
registered letters) should be documented in the participant’s medical record. 
• A participant who continues to be unreachable or continues to be noncompliant with 
study visits or procedures will be considered to have withdrawn from the study. 
• A participant should not be considered LTFU until due diligence has been completed. 

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7. 
STUDY ASSESSMENTS AND PROCEDURES  
Before performing any study procedures, all potential participants and/or participants’ 
parent/LAR will sign an ICF (as detailed in Section 10.2.6). Participants will undergo study 
procedures at the timepoints specified in the Part 1A SoA (Table 10), Part 1B SoA (Table 12), 
Part 1C (Table 13 and Table 14), Part 2 (Table 15 and Table 16), or Part 3 (Table 17 and 
Table 18). 
After the participant proceeds to the Participant Decision Clinic Visit (Part 1A) of the study, 
participants who received mRNA-1273 in Part 1A will continue to follow the open-label Part 1A 
SoA (Table 10). Participants who received placebo in Part 1A will transition to the open-label 
Part 1B of the study (Figure 10) and will follow the Part 1B SoA (Table 12). Participants in 
Part 1A or Part 1B who transitioned to Part 1C-1, at least 5 months from the last dose, will 
follow open-label Part 1C-1 SoA (Table 13) until study completion. Participants who remained 
blinded will follow Part 1A SoA. Participants who do not receive a BD will continue with their 
SoA (Part 1A or Part 1B). Eligible participants enrolled in Part 1C-2 will follow Part 1C-2 SoA 
(Table 14). Eligible participants enrolled in Part 2 will follow Part 2 SoA (Table 15 for 
participants who receive the booster dose and Table 16 for participants who do not receive the 
booster dose). Eligible participants enrolled in Part 3 will follow Part 3 SoA (Table 17 for 
participants who receive Dose 2 and Table 18 for participants who receive a single dose). 
A participant can also be seen for an unscheduled visit at any time during the study. An 
unscheduled visit may be prompted by reactogenicity issues, illness visit criteria for COVID-19, 
or new or ongoing AEs. The study site also has the discretion to make reminder telephone calls 
or send text messages to inform the participant about visits, review eDiary requirements, or 
follow-up on ongoing or outstanding issues. 
In accordance with “FDA Guidance on Conduct of Clinical Trials of Medical Products during 
COVID-19 Public Health Emergency” (DHHS 2020), investigators may convert study site visits 
to home visits or telemedicine visits with the approval of the Sponsor. Such action should be 
taken to protect the safety and well-being of study participants and study site staff or to comply 
with state or municipal mandates. 
General considerations for study assessments and procedures include the following: 
• Protocol waivers or exemptions are not allowed. The study procedures and their 
timing must be followed as presented in Table 10, Table 12, Table 13, Table 14, 
Table 15, Table 16, Table 17, and Table 18. Adherence to the study design 
requirements is essential and required for study conduct. 
• Immediate safety concerns should be discussed with the Sponsor immediately upon 
occurrence or awareness to determine if the participant should continue study 
treatment or participation in the study. 
• All screening evaluations must be completed and reviewed to confirm that potential 
participants meet all eligibility criteria. The investigator will maintain a screening log 
to record details of all participants screened and to confirm eligibility or record 
reasons for screening failure, as applicable. 

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• Procedures conducted as part of the participant’s routine clinical management (eg, 
blood count) and obtained before signing of the ICF may be utilized for screening or 
baseline assessments provided the procedures met the protocol-specified criteria and 
were performed within the time frame defined in the SoA. 
7.1. 
Safety Assessments and Procedures  
In Part 1A (blinded), Part 1B (open-label), Part 1C (open-label), Part 2 (open-label), and Part 3 
(open-label) safety assessments will include monitoring and recording of the following for each 
participant, according to the SoA (Table 10, Table 12, Table 13, Table 14, Table 15, Table 16, 
Table 17, and Table 18): 
• Solicited local and systemic ARs (Section 7.5.3) that occur during the 7 days 
following each injection (ie, the day of injection and 6 subsequent days) in Part 1A, 
Part 1C, Part 2, and Part 3. Solicited ARs will be recorded daily using eDiaries 
(Section 7.1.1). 
• Unsolicited AEs observed or reported during the 28 days following each injection (ie, 
the day of injection and 27 subsequent days) in Part 1A, Part 1C, Part 2, and Part 3. 
Unsolicited AEs are defined in Section 7.5.1. 
• AEs leading to discontinuation from dosing (except for participants who receive a 
single dose in Part 3) and/or withdrawal from study participation from Day 1 through 
the last day of study participation in Part 1A, Part 1B, Part 1C, Part 2, and Part 3 (see 
Section 10.1, Appendix 1 for the SoAs). 
• MAAEs from first dose on Day 1 through the entire study period in Part 1A, Part 1B, 
Part 1C, Part 2, and Part 3 (see Section 10.1, Appendix 1 for the SoAs). 
• SAEs from first dose on Day 1 through the entire study period in Part 1A, Part 1B, 
Part 1C, Part 2, and Part 3 (see Section 10.1, Appendix 1 for the SoAs). 
• AESIs through the entire study period in Part 1A, Part 1B, Part 1C, Part 2, and Part 3 
(see Section 10.1, Appendix 1 for the SoAs). 
• Vital sign measurements (Section 7.1.4). 
• Physical examination findings (Section 7.1.5). 
• Assessments for SARS-CoV-2 infection from Day 1 through study completion 
(Section 7.1.6). 
• Details of all pregnancies in female participants will be collected after the start of 
study treatment and until the end of their participation in the study (Section 7.5.6). 
7.1.1. 
Use of Electronic Diaries  
At the time of consent/assent, participants or their caregivers must confirm they will be willing to 
complete an eDiary using either an application downloaded to their smartphone or using a device 
that is provided at the time of enrollment. Before enrollment on Day 1, participants or their 
caregivers will be instructed to download the eDiary application or will be provided an eDiary 
device to record solicited ARs (Section 7.5.3) on Day 1. Participants who were originally 

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randomized to placebo and who opt to receive mRNA-1273 will enter the Open-label 
Observational Phase. They will receive Dose 1 at Day 209 (OL-Day 1), return for their second 
dose at OL-Day 29, and return again at OL-Day 57. Participants who entered the open-label 
phase, may opt to receive a BD in Part 1C-1, and will follow Part 1C-1 SoA until study 
completion. During the open-label period Part 1B, the eDiary will not be used. During the 
open-label Part 1C-1, Part 1C-2, Part 2, and Part 3, the eDiary will be used to record solicited 
ARs. 
In Part 1A, the Blinded Phase, Part 2, and Part 3 at each injection visit, participants or their 
caregivers will be instructed (Day 1) or reminded (Day 29 for Part 1A and Part 2, and Day 181 
for Part 3) on thermometer usage to measure body temperature, ruler usage to measure injection 
site erythema and swelling/induration (hardness), and self-assessment for localized axillary 
swelling or tenderness on the same side as the injection arm. 
In Part 1A, the Blinded Phase, Part 2, and Part 3 at each injection visit, participants or their 
caregivers will record data into the eDiary starting approximately 30 minutes after injection 
under supervision of the study site staff to ensure successful entry of assessments. The study site 
staff will perform any retraining as necessary. Participants or their caregivers will continue to 
record data in the eDiary after they leave the study site, preferably in the evening and at the same 
time each day, on the day of injection and for 6 days following injection. 
Participants or their caregivers will record the following data in the eDiary: 
• Solicited local and systemic reactogenicity ARs, as defined in Section 7.5.3, that 
occur on the day of each vaccine administration and during the 7 days after vaccine 
administration (ie, the day of injection and 6 subsequent days). If a solicited local or 
systemic AR continues beyond Day 7 after vaccination, the participant will be 
prompted to capture details of the solicited local or systemic AR in the eDiary until it 
is resolves or the next IP injection occurs, whichever occurs first; capture of details of 
ARs in the eDiary should not exceed 28 days after each vaccination. ARs recorded in 
the eDiary beyond Day 7 should be reviewed by the study site staff either during the 
next scheduled telephone call or at the next study site visit. 
• Daily oral body temperature measurement should be performed at approximately the 
same time each day using the thermometer provided by the study site. If body 
temperature is taken more than once in a given day, only the highest temperature 
reading should be recorded. 
• Measurement, as applicable, for solicited local ARs (injection site erythema and 
swelling/induration); the size measurements will be performed using the ruler 
provided by the study site. 
• Any medications taken to treat or prevent pain or fever on a day of injection or for the 
next 6 days. 
The eDiary will be the only source documents allowed for solicited systemic or local ARs 
(including body temperature measurements). Participants or their caregivers will be instructed to 
complete eDiary entries daily. The participant or their caregiver will have a limited window on 
the following day to complete assessments for the previous day; quantitative temperature 

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recordings and measurement of any injection site erythema or swelling/induration reported on 
the following day may be excluded from the analyses of solicited ARs. 
Any new safety information reported during safety telephone calls or at study site visits 
(including a solicited reaction) that is not already captured in the eDiary will be described in the 
source documents as a verbally reported event. An event reported in this manner must be 
described as a solicited event and entered on the solicited AR eCRF. 
Study site staff will review eDiary data with participants at visit(s) 7 days after each injection. 
The eDiary will also be used every 4 weeks, starting at Day 71 through Day 183 and again 
starting at Day 223 through Day 363 for participants in Part 1A (Table 10), on Day 191 through 
Day 303 and again on Day 343 through Day 455 in Part 2 for participants who receive the 
booster dose (Table 15), and on Day 99 through Day 183 and again on Day 223 through Day 307 
in Part 2 for participants who do not receive the booster dose (Table 16) to capture the 
occurrence of AEs, MAAEs, SAEs, AESI, or AEs leading to withdrawal. As specified in the 
applicable SoA (Table 10, Table 15, and Table 16), the eDiary will prompt the participant to 
complete an eDiary questionnaire that collects the following data: 
• Changes in health since last completing the questionnaire or since in contact with the 
study site. 
• Known exposure to someone with known COVID-19 or SARS-CoV-2 infection. 
• Any experience of symptoms of COVID-19. 
• Any MAAEs or SAEs. 
If an eDiary record results in identification of relevant safety events according to the study 
period, or of symptoms of COVID-19, a follow-up safety telephone call will be triggered. 
Completion of eDiary questionnaires will alternate with safety telephone calls (Section 7.1.2) as 
the procedure for safety follow-up approximately every 4 weeks starting at Day 85 through 
Day 197 and again starting at Day 237 through Day 377 (Part 1A SoA, Table 10), every 4 weeks 
starting at Day 205 through Day 317 and starting again at Day 357 through Day 469 (Part 2, 
Table 15 for participants who receive the booster dose), every 4 weeks starting at Day 113 
through Day 197 and again starting at Day 237 through Day 321 (Part 2, Table 16 for 
participants who do not receive the booster dose), every 6 weeks starting at Day 99 through 
Day 141 (Part 3, Table 17 for participants who receive Dose 2), and every 6 weeks starting at 
Day 99 through Day 141 (Part 3, Table 18 for participants who receive a single dose). 
In Part 1C-1 and Part 1C-2, diary entries will be recorded by the participant at approximately 
30 minutes after BD injection while at the study site with instruction provided by study staff. 
Study participants will continue to record entries in the eDiary each day after they leave the 
study site, preferably in the evening, on the day of injection and for 6 days following injection. If 
a solicited local or systemic AR continues beyond Day 7 after vaccination, the participant will be 
prompted to capture details of the solicited local or systemic AR in the eDiary until the AR 
resolves; capture of details of ARs in the eDiary should not exceed 28 days after vaccination. 
ARs recorded in eDiaries beyond Day 7 should be reviewed either via telephone call or at the 
following study visit. Review of eDiary will occur on BD-Day 8. 

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7.1.1.1. 
Ancillary Supplies for Participant Use  
Study sites will distribute Sponsor-provided oral thermometers and rulers for use by participants 
in assessing body temperature and injection site reactions for recording solicited ARs in eDiaries. 
Based on availability, smartphone devices may be provided to those participants who do not 
have their own device to use for eDiary activities. 
7.1.2. 
Safety Telephone Calls  
A safety telephone call is a telephone call made to the participant by trained study site personnel. 
This call will follow a script, which will facilitate the collection of relevant safety information. 
Safety telephone calls follow a schedule for each participant as indicated in the Part 1A SoA 
(Table 10), Part 1B (Table 12), Part 1C (Table 13 and Table 14), Part 2 (Table 15 and Table 16), 
and Part 3 (Table 17 and Table 18). 
The participant will be interviewed according to the script about occurrence of AEs, MAAEs, 
SAEs, AESI, AEs leading to study withdrawal, concomitant medications associated with those 
events, and any nonstudy vaccinations (Section 7.5.7). In addition, study personnel will collect 
information on known participant exposure to someone with known COVID-19 or SARS-CoV-2 
infection and on participant experience of COVID-19 symptoms. All safety information 
collected from the telephone contact must be documented in source documents as described by 
the participant and not documented on the script used for the safety telephone contact. As noted 
in Section 7.1.1, an unscheduled follow-up safety telephone call may be triggered if an eDiary 
record results in identification of a relevant safety event. 
7.1.3. 
Safety Laboratory Assessments  
No scheduled laboratory assessments for safety are planned. This is based on the absence of 
clinically significant abnormal laboratory findings in the Phase 1 and Phase 2 studies of 
mRNA-1273 in adults. 
A point-of-care urine pregnancy test will be performed at the Screening Visit (Day 0) and before 
each vaccine dose. At any time, a pregnancy test either via blood or point-of-care urine can be 
performed, at the discretion of the investigator. 
7.1.4. 
Vital Sign Measurements  
Vital sign measurements will include systolic and diastolic blood pressure, heart rate, respiratory 
rate, and body temperature (preferred route is oral). The participant will be seated for at least 
5 minutes before all measurements are taken. Vital signs will be measured at the timepoints 
indicated in the SoAs (Table 10, Table 12, Table 13, Table 14, Table 15, Table 16, Table 17, and 
Table 18). At dosing visits, vital sign measurements will be collected once before injection and 
at least 30 minutes post injection (before participants are discharged from the study site). 
Febrile participants at dosing visits (fever is defined as a body temperature ≥38.0°C/≥100.4°F) 
may have visits rescheduled within the relevant study visit windows. Afebrile participants with 
minor illnesses may be injected at the discretion of the investigator. 
When procedures overlap and are scheduled to occur at the same timepoint, the order of 
procedures should be vital sign measurements and then the blood collection. 

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7.1.5. 
Physical Examinations  
A full physical examination, including height and weight, will be performed at scheduled 
timepoints as indicated in the Part 1A (Table 10), Part 1B (Table 12), and Part 1C (Table 13 and 
Table 14), Part 2 (Table 15 and Table 16), and Part 3 (Table 17 and Table 18) SoAs. The full 
examination will include assessment of skin, head, ears, eyes, nose, throat, neck, thyroid, lungs, 
heart, cardiovascular system, abdomen, lymph nodes, and musculoskeletal system/extremities. 
Any clinically significant finding identified during a study visit should be reported as a MAAE. 
Symptom-directed physical examinations may be performed at other timepoints at the discretion 
of the investigator. On each injection day before injection and again 7 days after injection, the 
arm receiving the injection should be examined and the associated lymph nodes should be 
evaluated. Any clinically significant finding identified during a study visit should be reported as 
a MAAE. 
Body mass index will be calculated at the Screening Visit (Day 0) only. 
7.1.6. 
Assessment for SARS-CoV-2 Infection  
Study participants will have NP or nasal swab samples collected for SARS-CoV-2 testing at 
timepoints specified in the SoA (Part 1A, Table 10; Part 1B, Table 12; Part 1C, Table 13 and 
Table 14; Part 2, Table 15 and Table 16; and Part 3, Table 17 and Table 18). 
For Part 1A, Part 1B, Part 1C, Part 2, and Part 3, a study illness visit or a consultation will be 
arranged within 72 hours or as soon as possible to collect an NP or nasal swab sample to 
ascertain the presence of SARS-CoV-2 via RT-PCR if a participant experiences any of the 
following: 
• Signs or symptoms of SARS-CoV-2 infection as defined by the CDC (CDC 2020b). 
• Exposure to an individual confirmed to be infected with SARS-CoV-2. 
• MAAE suggesting a SARS-CoV-2 infection. 
If the participant had known exposure to COVID-19 (eg, exposure to someone with confirmed 
COVID-19), it will be captured in the COVID-19 exposure form. 
If scheduled, the study illness visit may collect additional clinical information, including 
assessments such as medical history, physical examination, blood sampling for clinical 
laboratory testing, and nasal, saliva, and/or NP swab sampling for viral PCR (including 
multiplex PCR for respiratory viruses including SARS-CoV-2) to evaluate the severity of the 
clinical case. Radiologic imaging studies may be conducted. All findings will be recorded in the 
eCRF. 
If participants are confirmed to have SARS-CoV-2 infection, the investigator will notify the 
participant, and the participant’s primary care physician, of the diagnosis. If the study participant 
does not have a primary care physician, the investigator will assist them to obtain one. The 
participant will also be instructed on infection prevention measures consistent with local public 
health guidance. 
Any confirmed symptomatic SARS-CoV-2 infection occurring in participants will be captured as 
a MAAE along with relevant concomitant medications and details about severity, seriousness, 
and outcome. Additionally, a convalescent visit will be scheduled approximately 28 days 

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(+7 days) after diagnosis (Section 7.4.3). At this visit, an NP or nasal swab sampling for viral 
PCR and a blood sample will be collected for potential immunologic assessment of 
SARS-CoV-2 infection. 
During the ongoing Omicron-related surge in SARS-CoV-2 infections or if any variant of 
concern-related surge may occur the following alternative process may be used for 
assessment of SARS-CoV-2 infection: 
If an illness visit is not possible due to COVID-19 related restrictions at site or in the wider 
community, a telehealth visit combined with a local diagnostic test, to be recorded under an 
unscheduled visit eCRF page, can substitute for a clinic visit. 
If due to COVID-19 related restrictions in the community, the participant’s LAR performed a 
home test rather than obtaining a test performed by a health care professional, the following 
process should apply: 
• If the participant reports symptoms but home test was negative, the investigator may 
report symptoms as ‘upper respiratory infection’ or other appropriate AE and report 
the negative home test on the local diagnostic lab page for an unscheduled visit, and 
forego the illness visit. 
• If the participant reports symptoms and the home test was positive, the investigator 
should encourage the family to seek confirmatory PCR-based testing at a local testing 
center or return to site for an illness visit. 
• If a local confirmatory PCR-based test is obtained, the investigator may report the 
result under an unscheduled visit and forego the illness visit. A convalescent visit 
should be scheduled if feasible. 
• If due to COVID-19 related restrictions at the site or in the community, neither a local 
test nor an illness visit is feasible, the investigator may report the result of the home 
test under the local diagnostic lab page as an unscheduled visit and forego the illness 
visit. A convalescent visit should be scheduled if feasible. 
7.2. 
Immunogenicity Assessments  
Blood samples for immunogenicity assessments will be collected at the timepoints indicated in 
the SoA (Part 1A, Table 10; Part 1B, Table 12; Part 1C, Table 13 and Table 14; Part 2, Table 15 
and Table 16; and Part 3, Table 17 and Table 18): The following analytes will be measured: 
• Serum nAb level against SARS-CoV-2 as measured by pseudovirus and/or live virus 
neutralization assays 
− Serum bAb levels against SARS-CoV-2 as measured by a multiplex serology 
assay specific to the SARS-CoV-2 S, N, RBD protein. 
Serum collected from all participants will be tested for bAb against SARS-CoV-2 nucleocapsid 
protein at specified timepoints. In addition, serum samples from a selected subset of study 
participants who received mRNA-1273 or mRNA-1273.222 will be selected for testing of nAb 
and bAb against the SARS-CoV-2 S protein. Sample aliquots will be designed to ensure that 
backup samples are available and that vial volumes are likely to be adequate for future testing 
needs. The actual time and date of each sample collected will be recorded in the eCRF, and 

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unique sample identification will be utilized to maintain the blind at the laboratory at all times 
and to allow for automated sample tracking and housing. Handling and preparation of the 
samples for analysis, as well as shipping and storage requirements, will be provided in a separate 
study manual. 
Measurement of bAb and nAb levels will be performed in a laboratory designated by the 
Sponsor. 
According to the ICF (Section 10.2.6), serum from immunogenicity testing may be used for 
future research, which may be performed at the discretion of the Sponsor to further characterize 
the immune response to SARS-CoV-2, additional assay development, and the immune response 
across CoVs. 
The maximum planned volume of blood sampled per participant for immunogenicity 
assessments in 1 day is 21 mL. 
7.3. 
Exploratory Assessments and Biomarkers  
Exploratory assessments may include assessment of biomarkers for safety, reactogenicity, 
inflammatory and cardiac function. Serologic markers of disease severity, immune response to 
SARS-CoV-2, RT-PCR of NP or nasal swab or saliva samples, and genetic sequences of 
SARS-CoV-2 strains isolated from participants’ samples may also be measured. 
7.4. 
Efficacy Assessments  
7.4.1. 
Vaccine Effectiveness Assessments  
Vaccine effectiveness for adolescents of ages of 12 to < 18 years will be inferred based on serum 
Ab responses obtained on Day 57 (28 days after the second injection of mRNA-1273) and 
Day 209 (28 days after the second injection of mRNA1273.222). Inference will be based on 
assessing the adolescent Ab responses against the following: 
1. If available at the time of analysis, adolescent Ab responses will be assessed against an 
accepted serum nAb threshold conferring protection against COVID-19. 
2. If an accepted threshold of protection is not available, adolescent Ab responses will be 
assessed by establishing noninferiority of the GM value and SRR of serum nAb from 
adolescent participants compared with those from young adults enrolled in the ongoing 
clinical endpoint efficacy trial (Study P301). The statistical parameters to infer 
effectiveness are described in Section 2. 
COVID-19: 
To be considered as a case of COVID-19 for the evaluation of the primary efficacy endpoint, the 
following case definition must be met: 
• The participant must have experienced at least TWO of the following systemic 
symptoms: Fever (≥38ºC/≥100.4ºF), chills, myalgia, headache, sore throat, new 
olfactory and taste disorder(s), OR 

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• The participant must have experienced at least ONE of the following respiratory 
signs/symptoms: cough, shortness of breath or difficulty breathing, OR clinical or 
radiographical evidence of pneumonia; AND 
• The participant must have at least 1 NP or nasal swab or saliva sample (or 
respiratory sample, if hospitalized) positive for SARS-CoV-2 by RT-PCR. 
Severe COVID-19: 
To be considered severe COVID-19, the following criteria must be met: 
• Confirmed COVID-19 as per the primary efficacy endpoint case definition, plus any 
of the following: 
− Clinical signs indicative of severe systemic illness, respiratory rates ≥30 per 
minute, heart rate ≥125 beats per minute, SpO2 ≤93% on room air at sea level or 
PaO2/FIO2 < 300 mm Hg, OR 
− Respiratory failure or Acute Respiratory Distress Syndrome, (defined as needing 
high-flow oxygen, noninvasive or mechanical ventilation, or ECMO), evidence of 
shock (systolic BP < 90 mmHg, diastolic BP < 60 mmHg or requiring 
vasopressors), OR 
− Significant acute renal, hepatic, or neurologic dysfunction, OR 
− Admission to an ICU or death. 
The secondary case definition of COVID-19 is defined as the following systemic symptoms: 
fever (temperature >38ºC/≥100.4ºF), or chills, cough, shortness of breath or difficulty breathing, 
fatigue, muscle aches, or body aches, headache, new loss of taste or smell, sore throat, 
congestion or runny nose, nausea, or vomiting or diarrhea AND a positive NP or nasal swab or 
saliva sample for SARS-CoV-2 by RT-PCR. 
Death attributed to COVID-19 is defined as any participant who dies during the study with a 
cause directly attributed to a complication of COVID-19. 
SARS-CoV-2 Infection: 
• SARS-CoV-2 infection is defined in participants with SARS-CoV-2 negative at 
baseline: 
− bAb level against SARS-CoV-2 nucleocapsid protein negative at Day 1, which 
becomes positive post baseline, OR 
− Post baseline-Positive RT-PCR. 
7.4.2. 
Surveillance for COVID-19 Symptoms  
Surveillance for COVID-19 symptoms will be conducted via biweekly telephone calls or eDiary 
prompts as specified in Section 7.1.1 and Figure 9; starting after participant enrollment and 
throughout the study. 
If there is no response to an eDiary prompt for 3 days, the study site staff will contact the study 
participant by phone. 

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According to the CDC as of 10 Jun 2020 (CDC 2020c), patients with COVID-19 have reported a 
wide range of symptoms ranging from mild symptoms to severe illness. Throughout the study, to 
survey for COVID-19, the following prespecified symptoms that meet the criteria for suspicion 
of COVID-19 will be elicited weekly from the participant and the presence of any one of these 
symptoms lasting at least 48 hours (except for fever and/or respiratory symptoms) will result in 
the study site staff arranging an illness visit to collect an NP or nasal swab within 72 hours: 
• Fever (temperature ≥38ºC/≥100.4ºF) or chills (of any duration, including ≤48 hours). 
• Shortness of breath or difficulty breathing (of any duration, including ≤48 hours). 
• Cough (of any duration, including ≤48 hours). 
• Fatigue. 
• Muscle or body aches. 
• Headache. 
• New loss of taste or smell. 
• Sore throat. 
• Congestion or runny nose. 
• Nausea or vomiting. 
• Diarrhea. 

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Figure 9: 
Surveillance for COVID-19 Symptoms and the Corresponding Clinical Data 
Pathways 
 
Abbreviations: BP = blood pressure, COVID-19 = coronavirus disease 2019, ECMO, SpO2 = oxygen saturation, 
PaO2 = partial pressure of oxygen, FIO2 = fraction of inspired oxygen, HCP = healthcare practitioner, 
RT-PCR = reverse transcriptase polymerase chain reaction, SARS-CoV-2 = Severe Acute Respiratory Syndrome 
coronavirus 2. 
It is important to note that some of the symptoms of COVID-19 overlap with solicited systemic 
ARs that are expected after vaccination with mRNA-1273 (eg, myalgia, headache, fever, and 
chills). During the first 7 days after vaccination, when these solicited ARs are common, 
investigators should use their clinical judgment to decide if an NP or nasal swab should be 
collected. The collection of an NP or nasal swab prior to each vaccination can help ensure that 
cases of COVID-19 are not overlooked. Any study participant who reports respiratory symptoms 
during the 7-day period after vaccination should be evaluated for COVID-19. 
During the course of the study, participants with symptoms of COVID-19 will be asked to return 
within 72 hours or as soon as possible to the study site or medically qualified staff from the study 
site will conduct a home visit as soon as possible to collect an NP or nasal swab sample (for 

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RT-PCR) for evaluation of COVID-19. Both study site visits and home visits are referred to as 
illness visits (Section 7.1.6). The NP or nasal swab sample will also be tested for the presence of 
other respiratory infections. Additionally, a convalescent visit will be scheduled approximately 
28 days (+7 days) after diagnosis (for Part 1A and 1B only) (Section 7.4.3). At this visit, an NP 
or nasal swab sampling for viral PCR and a blood sample will be collected for potential 
immunologic assessment of SARS-CoV-2 infection. In addition, the study site may collect an 
additional respiratory sample for SARS-CoV-2 testing to be able to render appropriate medical 
care for the study participant as determined by local standards of care. 
Cases are defined as participants meeting clinical criteria based both on symptoms for 
COVID-19 and on RT-PCR detection of SARS-CoV-2 from samples collected within 72 hours 
of the study participant reporting symptoms meeting the definition of COVID-19. Participants 
who are hospitalized for COVID-19 without the opportunity for a clinic or home visit will also 
be considered cases, assuming that the symptomology criteria for COVID-19 are met and a 
respiratory sample is positive for SARS-CoV-2 by PCR at a clinical laboratory improvement 
amendments-certified laboratory. Investigators are encouraged to try to obtain a respiratory 
sample during the course of hospitalization for submission to the study central laboratory, if 
feasible. The investigator should determine if the criteria for severe COVID-19 has been met. 
Severe COVID-19 is defined in Section 7.4.1. 
All clinical findings will be recorded in the eCRF. All confirmed cases of COVID-19 will be 
captured as MAAEs, along with relevant concomitant medications and details about severity, 
seriousness, and outcome, and will be reported immediately to the Sponsor or designee 
(Section 7.5.4). 
7.4.3. 
Follow-up/Convalescent Period After Diagnosis with COVID-19  
Any confirmed symptomatic COVID-19 occurring in a participant will be captured as a MAAE 
along with relevant concomitant medications and details about severity, seriousness, and 
outcome. A convalescent visit will be scheduled approximately 28 days (+7 days) after diagnosis 
(for Part 1A and Part 1B only). At this visit, an NP or nasal swab sampling for viral PCR and a 
blood sample will be collected for potential immunologic assessment of SARS-CoV-2 infection. 
The investigator should determine if the criteria for severe COVID-19 has been met. If the 
participant is hospitalized, medically qualified study site personnel will try to obtain medical 
records and SARS-CoV-2 diagnostic results. If the participant is later discharged from the 
hospital during the 28-day period following diagnosis of COVID-19, the study site personnel 
will arrange for a resumption of the protocol schedule. 
Convalescent visits are not applicable to Part 1C-1, Part 1C-2, Part 2, and Part 3. 
7.5. 
Safety Definitions and Related Procedures  
7.5.1. 
Adverse Event  
An AE is defined as any untoward medical occurrence associated with the use of a drug in 
humans, whether or not considered drug related. 

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Events Meeting the Adverse Event Definition 
• Exacerbation of a chronic or intermittent pre-existing condition including either an 
increase in frequency and/or intensity of the condition 
• New conditions detected or diagnosed after the first dose of IP even though they may 
have been present before the start of the study 
Events NOT Meeting the Adverse Event Definition 
• Medical or surgical procedure (eg, endoscopy, appendectomy): the condition that 
leads to the procedure should be the AE. 
• Situations in which an untoward medical occurrence did not occur (social and/or 
convenience admission to a hospital). 
An AR is any AE for which there is a reasonable possibility that the vaccine caused the AE 
(Section 7.5.9). For the purposes of investigational new drug safety reporting, “reasonable 
possibility” means that there is evidence to suggest a causal relationship between the vaccine and 
the AE. 
An unsolicited AE is any AE reported by the participant that is not specified as a solicited AR in 
the protocol or is specified as a solicited AR but starts outside the protocol-defined period for 
reporting solicited ARs (ie, for the 7 days after each dose of vaccine). 
7.5.2. 
Serious Adverse Events  
An AE (including an AR) is considered an SAE if, in the view of either the investigator or 
Sponsor, it results in any of the following outcomes: 
• Death 
A death that occurs during the study or that comes to the attention of the investigator 
during the protocol-defined follow-up period must be reported to the Sponsor, 
whether or not it is considered related to the IP. 
• Is life-threatening  
An AE is considered life-threatening if, in the view of either the investigator or the 
Sponsor, its occurrence places the participant at immediate risk of death. It does not 
include an AE that, had it occurred in a more severe form, might have caused death. 
• Inpatient hospitalization or prolongation of existing hospitalization 
In general, inpatient hospitalization indicates the participant was admitted to the 
hospital or emergency ward for at least one overnight stay for observation and/or 
treatment that would not have been appropriate in the physician’s office or outpatient 
setting. The hospital or emergency ward admission should be considered an SAE 
regardless of whether opinions differ as to the necessity of the admission. 
Complications that occur during inpatient hospitalization will be recorded as an AE; 
however, if a complication/AE prolongs hospitalization or otherwise fulfills SAE 
criteria, the complication/AE will be recorded as a separate SAE. 

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• Persistent or significant incapacity or substantial disruption of the ability to 
conduct normal life functions 
This definition is not intended to include experiences of relatively minor medical 
significance such as uncomplicated headache, nausea/vomiting, diarrhea, influenza, 
and accidental trauma (eg, sprained ankle), which may interfere with or prevent 
everyday life functions but do not constitute a substantial disruption. 
• Congenital anomaly or birth defect. 
• Medically important event  
Medical judgment should be exercised in deciding whether SAE reporting is 
appropriate in other situations, such as important medical events that may not be 
immediately life-threatening or result in death or hospitalization but may jeopardize 
the participant or require medical or surgical intervention to prevent one of the other 
outcomes listed in the above definition. These events should usually be considered 
serious. Examples of such medical events include allergic bronchospasm requiring 
intensive treatment in an emergency room or at home, blood dyscrasias or 
convulsions that do not result in inpatient hospitalization, or the development of drug 
dependency or drug abuse. 
7.5.3. 
Solicited Adverse Reactions  
The term “reactogenicity” refers to the occurrence and intensity of selected signs and symptoms 
(ARs) occurring after IP injection. The eDiary will solicit daily participant reporting of ARs 
using a structured checklist (Section 7.1.1). Participants will record such occurrences in an 
eDiary on the day of each dose injection and for the 6 days after the day of dosing (Part 1A, 
Part 1C, Part 2, and Part 3 only). 
Severity grading of reactogenicity will occur automatically based on participant entry into the 
eDiary according to the grading scales presented in Table 6 modified from the Toxicity Grading 
Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventative Vaccine Clinical 
Trials (DHHS 2007). 
If a solicited local or systemic AR continues beyond Day 7 after vaccination, the participant will 
be prompted to capture details of the solicited local or systemic AR in the eDiary until it resolves 
or the next IP injection occurs whichever occurs first; capture of details of ARs in the eDiary 
should not exceed 28 days after each vaccination. ARs recorded in the eDiary beyond Day 7 
should be reviewed by the study site staff either during the next scheduled telephone call or at 
the next study site visit. All solicited ARs (local and systemic) will be considered causally 
related to dosing. 

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Table 6: 
Solicited Adverse Reactions and Grades  
Reaction 
Grade 0 
Grade 1 
Grade 2 
Grade 3 
Grade 4a 
Injection site pain 
None 
Does not 
interfere with 
activity  
Repeated use of over-
the-counter pain 
reliever > 24 hours or 
interferes with activity  
Any use of 
prescription pain 
reliever or 
prevents daily 
activity 
Requires 
emergency 
room visit or 
hospitalization 
Injection site 
erythema (redness) 
< 25 mm/ 
 < 2.5 cm 
25 – 50 mm/ 
2.5 – 5 cm 
51 – 100 mm/ 
5.1 – 10 cm 
> 100 mm/ 
> 10 cm 
Necrosis or 
exfoliative 
dermatitis 
Injection site 
swelling/induration 
(hardness) 
< 25 mm/ 
< 2.5 cm 
25 – 50 mm/ 
2.5 – 5 cm 
51 – 100 mm/ 
5.1 – 10 cm 
> 100 mm/ 
> 10 cm 
Necrosis  
Axillary (underarm) 
swelling or 
tenderness 
ipsilateral to the 
side of injection 
None 
No interference 
with activity 
Repeated use of over-
the-counter 
(nonnarcotic) pain 
reliever > 24 hours or 
some interference with 
activity 
Any use of 
prescription 
(narcotic) pain 
reliever or 
prevents daily 
activity 
Emergency 
room visit or 
hospitalization 
Headache 
None 
No interference 
with activity 
Repeated use of 
over-the-counter pain 
reliever > 24 hours or 
some interference with 
activity 
Significant; any 
use of 
prescription pain 
reliever or 
prevents daily 
activity 
Requires 
emergency 
room visit or 
hospitalization 
Fatigue 
None 
No interference 
with activity  
Some interference with 
activity 
Significant; 
prevents daily 
activity  
Requires 
emergency 
room visit or 
hospitalization 
Myalgia (muscle 
aches all over body) 
None 
No interference 
with activity  
Some interference with 
activity 
Significant; 
prevents daily 
activity  
Requires 
emergency 
room visit or 
hospitalization 
Arthralgia (joint 
aches in several 
joints) 
None 
No interference 
with activity  
Some interference with 
activity 
Significant; 
prevents daily 
activity  
Requires 
emergency 
room visit or 
hospitalization 
Nausea/vomiting 
None 
No interference 
with activity or 
1-2 episodes/ 
24 hours 
Some interference with 
activity or 
> 2 episodes/24 hours 
Prevents daily 
activity, requires 
outpatient 
intravenous 
hydration 
Requires 
emergency room 
visit or 
hospitalization 
for hypotensive 
shock 

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Reaction 
Grade 0 
Grade 1 
Grade 2 
Grade 3 
Grade 4a 
Chills 
None 
No interference 
with activity 
Some interference with 
activity not requiring 
medical intervention 
Prevents daily 
activity and 
requires medical 
intervention 
Requires 
emergency 
room visit or 
hospitalization 
Fever (oral) 
< 38.0°C 
< 100.4°F 
38.0 – 38.4°C 
100.4 – 101.1°F 
38.5 – 38.9°C 
101.2 – 102.0°F 
39.0 – 40.0°C 
102.1 – 104.0°F 
> 40.0°C 
> 104.0°F 
a. 
Grading for Grade 4 events per investigator assessment (with exception of fever). 
Source: Guidance for industry – Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in 
Preventative Vaccine Clinical Trials (DHHS 2007). 
Any solicited AR that meets any of the following criteria must be entered into the participant’s 
source document and must also be recorded by the study site staff on the solicited AR page of the 
participant’s eCRF: 
• Solicited local or systemic AR that results in a visit to an HCP; otherwise meets the 
definition of a MAAE 
• Solicited local or systemic AR leading to the participant withdrawing from the study 
or the participant being withdrawn from the study by the investigator (AE leading to 
withdrawal) 
• Solicited local or systemic AR lasting beyond 7 days after injection 
• Solicited local or systemic AR that leads to participant withdrawal from IP 
• Solicited local or systemic AR that otherwise meets the definition of an SAE 
7.5.4. 
Medically Attended Adverse Events  
A MAAE is an AE that leads to an unscheduled visit to an HCP. This would include visits to a 
study site for unscheduled assessments (eg, abnormal laboratory test results follow-up, 
COVID-19 [Section 7.4.1]) and visits to HCPs external to the study site (eg, urgent care, primary 
care physician). Investigators will review unsolicited AEs for the occurrence of any MAAE. 
Unsolicited AEs will be captured on the AE page of the eCRF. 
All confirmed symptomatic COVID-19 cases (Section 7.4.1) will be recorded as MAAEs and 
reported to the Sponsor or designee immediately and in all circumstances within 24 hours, using 
the SAE Mailbox, the SAE Hotline, or the SAE Fax line (Section 7.5.11). The investigator will 
submit any updated COVID-19 case data to the Sponsor within 24 hours of it being available. 
7.5.4.1. 
Anaphylaxis  
All suspected cases of anaphylaxis should be recorded as MAAEs and reported as SAEs 
(Section 7.5.2) based on criteria for a medically important event unless the event meets other 
serious criteria. As an SAE, the event should be reported to the Sponsor or designee immediately 
and in all circumstances within 24 hours as per Section 7.5.10 (Reporting SAEs). The 
investigator will submit any updated anaphylaxis case data to the Sponsor within 24 hours of it 
being available. For reporting purposes, a participant who displays signs/symptoms consistent 
with anaphylaxis as shown below should be reported as a potential case of anaphylaxis. This is 

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provided as general guidance for investigators and is based on the Brighton Collaboration case 
definition (Rüggeberg et al 2007). 
Anaphylaxis is an acute hypersensitivity reaction with multi-organ-system involvement that can 
present as or rapidly progress to a severe life-threatening reaction. It may occur following 
exposure to allergens from a variety of sources. Anaphylaxis is a clinical syndrome characterized 
by: 
• Sudden onset AND 
• Rapid progression of signs and symptoms AND 
• Involving 2 or more organ systems, as follows: 
− Skin/mucosal: urticaria (hives), generalized erythema, angioedema, generalized 
pruritus with skin rash, generalized prickle sensation, red and itchy eyes 
− Cardiovascular: measured hypotension, clinical diagnosis of uncompensated 
shock, loss of consciousness or decreased level of consciousness, evidence of 
reduced peripheral circulation 
− Respiratory: bilateral wheeze (bronchospasm), difficulty breathing, stridor, upper 
airway swelling (lip, tongue, throat, uvula, or larynx), respiratory distress, 
persistent dry cough, hoarse voice, sensation of throat closure, sneezing, 
rhinorrhea 
− Gastrointestinal: diarrhea, abdominal pain, nausea, vomiting 
7.5.5. 
Adverse Events of Special Interest  
An AESI is an AE (serious or nonserious) of scientific and medical concern specific to the 
Sponsor’s product or program, for which ongoing monitoring and immediate notification by the 
investigator to the Sponsor is required and documentation is in the form of a case narrative. Such 
events may require further investigation to characterize and understand them. Refer to 
Section 10.4, Appendix 4 for a list of AESIs pertinent to this study. All AESIs will be collected 
throughout the entire study period and must be reported to the Sponsor or designee immediately 
and in all circumstances within 24 hours of becoming aware of the event via the EDC system. If 
a site receives a report of a new AESI from a study participant or receives updated data on a 
previously reported AESI and the eCRF has been taken offline, then the site can report this 
information on a paper AESI form using the SAE Mailbox, the SAE Hotline, or the SAE Fax 
line (Section 7.5.11). 
7.5.5.1. 
Acute Myocarditis and/or Pericarditis  
These definitions are intended to serve as a guide to help in the reporting of suspected cases of 
myocarditis and/or pericarditis; however, the diagnosis of suspected cases is left to the 
investigator’s clinical judgment. 
The investigator’s medical judgment must be applied when parent(s)/LAR(s) report that a 
participant has symptoms concerning for myocarditis and/or pericarditis per the CDC case 
definition. Diagnostic evaluation (eg, EKG, echocardiogram) and laboratory testing (eg, 
troponin) per the CDC definition of myocarditis and/or pericarditis must be promptly obtained 

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for any participant with concerning signs/symptoms. Referral to a pediatric cardiologist should 
be obtained in those with positive test results or clinically significant symptoms without other 
identifiable causes. Additional testing and evaluation may be indicated. Once available, updated 
myocarditis, pericarditis, or myopericarditis case data will be submitted by the investigator to the 
Sponsor within 24 hours. 
All suspected cases of probable and confirmed myocarditis, pericarditis, or myopericarditis 
should be recorded as an AESI, and reported as an SAE, if the event meets seriousness criteria. 
As an SAE, the event should be reported to the Sponsor or designee immediately and in all 
circumstances within 24 hours as per Section 7.5.12. The investigator will submit any updated 
myocarditis, pericarditis, or myopericarditis case data to the Sponsor within 24 hours of it being 
available. For reporting purposes, a participant who displays signs/symptoms consistent with the 
CDC case definitions as described below (Gargano et al 2021), should be reported as a potential 
case of confirmed or probable myocarditis, pericarditis, or myopericarditis. 
7.5.5.2. 
Acute Myocarditis Case Definition  
Presence of ≥1 new or worsening of the following clinical symptoms (persons who lack the 
listed symptoms but who meet other criteria may be classified as subclinical myocarditis 
[probable or confirmed]): 
• Chest pain/pressure/discomfort 
• Dyspnea/shortness of breath/pain with breathing 
• Palpitations 
• Syncope 
OR 
Infants and children aged <12 years might instead have ≥2 of the following symptoms: 
• Irritability 
• Vomiting 
• Poor feeding 
• Tachypnea 
• Lethargy 
AND 
For PROBABLE CASE: 
Presence of ≥1 new finding of the following: 
• Troponin level above upper limit of normal (any type of troponin) 
• Abnormal ECG or EKG or rhythm monitoring findings consistent with myocarditis 
− To meet the ECG or rhythm monitoring criterion, a probable case must include at 
least one of the following: 
o ST segment or T-wave abnormalities 

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o Paroxysmal or sustained atrial, supraventricular, or ventricular arrhythmias 
o AV nodal conduction delays or intraventricular conduction defects 
• Abnormal cardiac function or wall motion abnormalities on echocardiogram 
• Cardiac MRI finding consistent with myocarditis (Ferreira et al 2018) 
AND 
• No other identifiable cause of the symptoms and findings 
For CONFIRMED CASE: 
• Histopathologic confirmation of myocarditis (using Dallas criteria [Aretz et al 1987]) 
OR 
• Cardiac magnetic resonance imaging findings consistent with myocarditis in the 
presence of troponin level above upper limit of normal (any type of troponin) 
AND 
• No other identifiable cause of the symptoms and findings 
7.5.5.3. 
Acute Pericarditis Case Definition  
Presence of ≥2 new or worsening of the following clinical features (Adler et al 2015): 
• Acute chest pain (Typically described as pain made worse by lying down, deep 
inspiration, or cough; and relieved by sitting up or leaning forward, although other 
types of chest pain may occur) 
• Pericardial rub on examination 
• New ST-elevation or PR-depression on EKG 
• New or worsening pericardial effusion on echocardiogram or magnetic resonance imaging 
7.5.5.4. 
Myopericarditis Case Definition  
Participants who meet criteria for both myocarditis and pericarditis may be described under 
myopericarditis. 
7.5.5.5. 
Multisystem Inflammatory Syndrome in Children Case Definition  
Investigators will also be asked to report, as AESI, clinical signs/symptoms consistent with the 
CDC case definition of MIS-C (https://emergency.cdc.gov/han/2020/han00432.asp): 
• An individual aged < 21 years presenting with fever, laboratory evidence of 
inflammation, and evidence of clinically severe illness requiring hospitalization, with 
multisystem (>2) organ involvement (cardiac, renal, respiratory, hematologic, 
gastrointestinal, dermatologic or neurological); 
AND 
• No alternative plausible diagnoses; 

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AND 
• Positive for current or recent SARS-CoV-2 infection by RT-PCR, serology, or 
antigen test; or COVID-19 exposure within the 4 weeks prior to the onset of 
symptoms: 
o Fever ≥ 38.0°C/≥ 100.4ºF for ≥ 24 hours, or report of subjective fever lasting 
≥24 hours 
o Including, but not limited to, one or more of the following: an elevated CRP, 
ESR, fibrinogen, procalcitonin, d-dimer, ferritin, LDH, or IL-6, elevated 
neutrophils, reduced lymphocytes, and low albumin 
Some individuals may fulfill full or partial criteria for Kawasaki disease but should be reported if 
they meet the case definition for MIS-C. Consider MIS-C in any pediatric death with evidence of 
SARS-CoV-2 infection. 
All cases of MIS-C will be reported to the Sponsor or designee immediately and in all 
circumstances within 24 hours, using the SAE Mailbox, the SAE Hotline, or the SAE Fax line 
(Section 7.5.11). 
7.5.6. 
Recording and Follow-up of Pregnancy  
Female individuals who have a positive pregnancy test at Screening should not be enrolled; 
participants who have a positive pregnancy test any time during the study should receive no 
further dosing with IP but should be asked to remain in the study and be monitored for safety. 
Details of all pregnancies in female participants will be collected after the start of study 
treatment and until the end of their participation in the study. 
• If a pregnancy is reported, the investigator should inform the Sponsor within 24 hours 
of learning of the pregnancy and should follow the procedures outlined in this section. 
• Abnormal pregnancy outcomes (eg, spontaneous abortion, fetal death, stillbirth, 
congenital anomalies, ectopic pregnancy) are considered SAEs. 
Pregnancies occurring in participants after enrollment must be reported to Sponsor or designee 
within 24 hours of the study site learning of its occurrence, using the SAE Mailbox, the SAE 
Hotline, or the SAE Fax line (Section 7.5.11). If the participant agrees to submit this information, 
the pregnancy must be followed to determine the outcome, including spontaneous or voluntary 
termination, details of the birth, and the presence or absence of any birth defects, congenital 
abnormalities, or maternal and/or newborn complications. This follow-up should occur even if 
intended duration of the safety follow-up for the study has ended. Pregnancy report forms will be 
distributed to the study site to be used for this purpose. The investigator must immediately 
(within 24 hours of awareness) report to the Sponsor any pregnancy resulting in an abnormal 
outcome according to the procedures described for SAEs. 
7.5.7. 
Eliciting and Documenting Adverse Events  
The investigator is responsible for ensuring that all AEs and SAEs are recorded in the eCRF and 
reported to the Sponsor. 

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Solicited ARs will be collected from Day 1 through 7 days after each dose in Part 1A, Part 1C, 
Part 2, and Part 3. Other (unsolicited) AEs will be collected from Day 1 through 28 days after 
each dose in Part 1A, Part 1C, Part 2, and Part 3. 
Both MAAEs and SAEs will be collected from participants as specified in the SoA until the end 
of their participation in Part 1A, Part 1B, Part C, Part 2, and Part 3. Any AEs that occur before 
administration of IP will be analyzed separately from AEs. 
At every study site visit or telephone contact, participants will be asked a standard question to 
elicit any medically related changes in their well-being (including COVID-19 symptoms) 
according to the scripts provided. Participants will also be asked if they have been hospitalized, 
had any accidents, used any new medications, changed concomitant medication regimens (both 
prescription and over-the-counter medications), or had any nonstudy vaccinations. 
In addition to participant observations, physical examination findings, or data relevant to 
participant safety classified as an AE will be documented on the AE page of the eCRF. 
After the initial AE/SAE report, the investigator is required to proactively follow each participant 
at subsequent visits/contacts. All AEs and SAEs will be treated as medically appropriate and 
followed until resolution, stabilization, the event is otherwise explained, or the participant is 
LTFU (as defined in Section 6.4). 
7.5.8. 
Assessment of Intensity  
An event is defined as “serious” when it meets at least one of the predefined outcomes as 
described in the definition of an SAE (Section 7.5.2), NOT when it is rated as severe. 
The severity (or intensity) of an AR or AE refers to the extent to which it affects the participant’s 
daily activities. The Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers 
Enrolled in Preventative Vaccine Clinical Trials (DHHS 2007) will be used to categorize local 
and systemic reactogenicity events (solicited ARs), and vital sign measurements observed during 
this study. Specific criteria for local and systemic reactogenicity events are presented in 
Section 7.5.3. 
The determination of severity for all unsolicited AEs should be made by the investigator based 
upon medical judgment and the definition of severity as follows: 
• Mild: These events do not interfere with the participant’s daily activities. 
• Moderate: These events cause some interference with the participant’s daily activities 
and require limited or no medical intervention. 
• Severe: These events prevent the participant’s daily activity and require intensive 
therapeutic intervention. 
Study staff should elicit from the participant the impact of AEs on the participant’s activities of 
daily living to assess severity and document appropriately in the participant’s source 
documentation. Changes in the severity of an AE should be documented in the participant’s 
source documentation to allow an assessment of the duration of the event at each level of 
intensity to be performed. An AE characterized as intermittent requires documentation of onset 
and duration of each episode. An AE that fluctuates in severity during the course of the event is 
reported once in the eCRF at the highest severity observed. 

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7.5.9. 
Assessment of Causality  
The investigator’s assessment of an AE’s relationship to IP is part of the documentation process 
but is not a factor in determining what is or is not reported in the study. 
The investigator will assess causality (ie, whether there is a reasonable possibility that the IP 
caused the event) for all AEs and SAEs. The relationship will be characterized using the 
following classification: 
Not related: There is not a reasonable possibility of a relationship to the IP. Participant did not 
receive the IP OR temporal sequence of the AE onset relative to administration of the IP is not 
reasonable OR the AE is more likely explained by another cause than the IP. 
Related: There is a reasonable possibility of a relationship to the IP. There is evidence of 
exposure to the IP. The temporal sequence of the AE onset relative to the administration of the IP 
is reasonable. The AE is more likely explained by the IP than by another cause. 
7.5.10. 
Reporting Adverse Events  
The investigator is responsible for reporting all AEs that are observed or reported during the 
study, regardless of their relationship to IP or their clinical significance. If there is any doubt as 
to whether a clinical observation is an AE, the event should be reported. 
All unsolicited AEs reported or observed during the study will be recorded on the AE page of the 
eCRF. Information to be collected includes the type of event, time of onset, 
investigator-specified assessment of severity (impact on activities of daily living) and 
relationship to IP, time of resolution of the event, seriousness, as well as any required treatment 
or evaluations, and outcome. The unsolicited AEs resulting from concurrent illnesses, reactions 
to concurrent illnesses, reactions to concurrent medications, or progression of disease states must 
also be reported. All AEs will be followed until they are resolved or stable or judged by the 
investigator to be not clinically significant. The MedDRA will be used to code all unsolicited 
AEs. 
Any medical condition that is present at the time that the participant is screened but does not 
deteriorate should not be reported as an unsolicited AE. However, if it deteriorates at any time 
during the study, it should be recorded as an unsolicited AE. 
7.5.11. 
Reporting SAEs  
Prompt notification by the investigator to the Sponsor of an SAE is essential so that legal 
obligations and ethical responsibilities toward the safety of participants and the safety of a study 
intervention under clinical investigation are met. 
Any AE considered serious by the investigator or that meets SAE criteria (Section 7.5.2) must be 
reported to the Sponsor immediately (within 24 hours of becoming aware of the SAE) via the 
EDC system. The investigator will assess whether there is a reasonable possibility that the IP 
caused the SAE. The Sponsor will be responsible for notifying the relevant regulatory authorities 
of any SAE as outlined in the 21 US CFR Part 312 and Part 320. The investigator is responsible 
for notifying the IRB directly. 
If the eCRF is unavailable at the time of the SAE, the following contact information is to be used 
for SAE reporting: 

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• SAE Mailbox: 
 
• SAE Fax line: 
 
Regulatory reporting requirements for SAE are described in Section 7.5.15. 
The investigator and any qualified designees are responsible for detecting, documenting, and 
recording events that meet the definition of an AE, including SAEs, and remain responsible for 
following up AEs that are serious, considered related to IP or study procedures, or that caused 
the participant to discontinue the study. 
7.5.12. 
Time Period and Frequency for Collecting AE and SAE Information  
Medical occurrences that begin before the start of IP dosing but after obtaining informed consent 
will be recorded in the Medical History/Current Medical Conditions Section of the eCRF and not 
in the AE Section; however, if the condition worsens at any time during the study, it will be 
recorded and reported as an AE. 
Adverse events may be collected as follows: 
• Observing the participant 
• Receiving an unsolicited complaint from the participant 
• Questioning the participant in an unbiased and nonleading manner 
Solicited ARs will be collected from the day of injection through 6 days after each dose. Other 
(unsolicited) AEs will be collected from the day of injection through 28 days after each dose. 
Serious AEs will be collected from the start of IP dosing until the last day of study participation. 
All SAEs will be recorded and reported to the Sponsor or designee immediately and in all 
circumstances within 24 hours. The investigator will submit any updated SAE data to the 
Sponsor within 24 hours of it being available. 
An abnormal value or result from a clinical or laboratory evaluation can also indicate an AE if it 
is determined by the investigator to be clinically significant (eg, leads to dose modification or 
study drug discontinuation, or meets any serious criteria). If this is the case, it must be recorded 
in the source document and as an AE on the appropriate AE form(s). The evaluation that 
produced the value or result should be repeated until that value or result returns to normal or is 
stabilized and the participant’s safety is not at risk. 
Investigators are not obligated to actively seek AEs or SAEs after EOS participation. However, if 
the investigator learns of any SAE (including a death) at any time after a participant has 
withdrawn from or completed the study, and the investigator considers the event to be reasonably 
related to the IP or study participation, the investigator must promptly notify the Sponsor. 
7.5.13. 
Method of Detecting AEs and SAEs  
Electronic diaries have specifically been designed for this study by the Sponsor. The diaries will 
include prelisted AEs (solicited ARs) and intensity scales; they will also include blank space for 
the recording of information on other AEs (unsolicited AEs) and concomitant 
medications/vaccinations. 
PPD
PPD

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The investigator is responsible for the documentation of AEs regardless of treatment group or 
suspected causal relationship to IP. For all AEs, the investigator must pursue and obtain 
information adequate to determine the outcome of the AE and to assess whether the AE meets 
the criteria for classification as an SAE requiring immediate notification to the Sponsor or its 
designated representative. 
Care will be taken not to introduce bias when detecting AEs and/or SAEs. Open-ended and 
nonleading verbal questioning of the participant is the preferred method to inquire about the 
occurrence of AE. 
7.5.14. 
Follow-up of AEs and SAEs  
After the initial AE/SAE report, the investigator is required to proactively follow each participant 
at subsequent visits and contacts. 
All AEs and SAEs will be treated as medically appropriate and followed until resolution, 
stabilization, the event is otherwise explained, or the participant is LTFU, as defined in 
Section 6.4. 
7.5.15. 
Regulatory Reporting Requirements for SAEs  
• Prompt notification by the investigator to the Sponsor of an SAE is essential so that 
legal obligations and ethical responsibilities toward the safety of participants and the 
safety of a study intervention under clinical investigation are met. 
• The Sponsor has a legal responsibility to notify both the local regulatory authority 
and other regulatory agencies about the safety of a study intervention under clinical 
investigation. The Sponsor will comply with country-specific regulatory requirements 
relating to safety reporting to the regulatory authority, IRBs, and investigators. 
• Investigator safety reports must be prepared for suspected unexpected serious adverse 
reaction according to local regulatory requirements and Sponsor policy and forwarded 
to investigators as necessary. 
• An investigator who receives an investigator safety report describing an SAE or other 
specific safety information (eg, summary or listing of SAEs) from the Sponsor will 
review and then file it along with the IB and will notify the IRB, if appropriate 
according to local requirements. 
7.6. 
Safety Monitoring  
The CRO’s medical monitor, the Sponsor’s medical monitor, and the individual study site 
investigators will monitor safety throughout the study. 
7.6.1. 
Data Safety Monitoring Board  
Safety oversight will be under the direction of a DSMB composed of external independent 
consultants with relevant expertise. Members of the DSMB will be independent from the study 
conduct and free of conflict of interest. 
For the blinded phase of Part 1 of the study, the DSMB will have separate meetings by 
teleconference to review unblinded safety data when half of the study population 

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(1500 randomized participants) have reached Day 8 (1 week after Dose 1) and again 
approximately when 25% (750), 50% (1500), and 75% (2250) of enrolled participants have 
reached Day 36 (1 week after Dose 2). Recruitment will continue, as applicable, during the 
DSMB review period. The DSMB will operate under the rules of an approved charter that will be 
written and reviewed at the organizational meeting of the DSMB. Details regarding the DSMB 
composition, responsibilities, procedures, and frequency of data review will be defined in its 
charter. 
For Part 2 and Part 3 of the study, the DSMB will convene on an ad hoc basis if any of the pause 
rules, described in Section 6.4, are met. The DSMB will review all available unblinded study 
data to adjudicate any potential study pauses and make recommendations on further study 
conduct, including requesting additional information, recommending stopping the study, 
recommending changes to study conduct and/or the protocol, or recommending additional 
operational considerations due to safety issues that arise during the study. 
7.6.2. 
Independent Cardiac Event Adjudication Committee  
An independent CEAC of medically qualified personnel, including cardiologists, will review all 
suspected cases of myocarditis and pericarditis to determine if they meet CDC criteria of 
“probable” or “confirmed” events which are reported in ongoing interventional clinical trials per 
the CEAC charter (Gargano et al 2021). Any case that the CEAC assesses as representing 
probable or confirmed cases of myocarditis or pericarditis will be referred to the Sponsor, who 
will then determine if additional action is needed. 
The CEAC will operate under the rules of an approved charter that will be written and reviewed 
at the organizational meeting of the CEAC. Details regarding the CEAC composition, 
responsibilities, procedures, and frequency of data review will be defined in its charter. 
7.7. 
Treatment of Overdose  
As the study treatment is to be administered by a healthcare professional, it is unlikely that an 
overdose will occur. Dose deviations will be tracked as protocol deviations (Section 10.2.8). 
7.8. 
Pharmacokinetics  
Pharmacokinetic parameters are not evaluated in this study. 
7.9. 
Pharmacodynamics  
Pharmacodynamic parameters are not evaluated in this study. 
7.10. 
Biomarkers  
Immunogenicity assessments are presented in Section 7.2. Biomarker plasma and biomarker 
serum samples will be stored for potential future biomarker assessment. 
7.11. 
Health Economics  
Health economics are not evaluated in this study. 

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8. 
STATISTICAL ANALYSIS PLAN  
This section summarizes the planned statistical analysis strategy and procedures for the study. 
The details of statistical analysis will be provided in the SAP, which will be finalized before the 
clinical database lock for the study. If changes are made to primary and/or key secondary 
objectives and hypotheses or the statistical methods related to those hypotheses after the study 
has begun but prior to any data unblinding, then the protocol will be amended (consistent with 
ICH Guideline E9). Changes to other secondary or exploratory analyses made after the protocol 
has been finalized, along with an explanation as to when and why they occurred, will be listed in 
the SAP or CSR for the study. Ad hoc exploratory analyses, if any, will be clearly identified in 
the CSR. 
8.1. 
Blinding and Responsibility for Analyses  
See Section 3.1.1.1 regarding the addition of a Participant Decision Visit as part of this protocol 
amendment. 
Part 1A of this study is observer-blind. The investigator, study staff, study participants, study site 
monitors, and Sponsor personnel (or its designees) will be blinded to the IP administered until 
study end or initiation of Part 1B or Part 1C or Part 2, with the following exceptions: 
• Unblinded pharmacy personnel (of limited number) will be assigned to vaccine 
accountability procedures and will prepare and administer mRNA-1273 (or placebo) 
to all participants. These pharmacy personnel will have no study functions other than 
study vaccine management, documentation, accountability, preparation, and 
administration. They will not be involved in participant evaluations and will not 
reveal the identity of IP to either the participant or the blinded study site personnel 
involved in the conduct of the study unless this information is necessary in the case of 
an emergency. 
• Unblinded study site monitors, not involved in other aspects of monitoring, will be 
assigned as the IP accountability monitors. They will have responsibilities to ensure 
that study sites are following all proper IP accountability, preparation, and 
administration procedures. 
• An unblinded statistical and programming team will perform the preplanned IA 
(Section 8.7.1). Sponsor team members will be prespecified to be unblinded to the IA 
results and will not communicate the results of IA to the blinded investigators, study 
site staff, clinical monitors, or participants. This is detailed in the study Data Blinding 
Plan. 
In Part 1A, the dosing assignment will be concealed by having the unblinded pharmacy 
personnel prepare the IP in a secure location that is not accessible or visible to other study staff. 
An opaque sleeve over the syringe used for injection will maintain the blind at the time of 
injection, as the doses containing mRNA-1273 will look different to that of placebo. Only 
delegated unblinded study site staff will conduct the injection procedure. Once the injection is 
completed, only the blinded study staff will perform further assessments and interact with the 
participants. Access to the randomization code will be strictly controlled at the pharmacy. 

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As documented in the study Data Blinding Plan, the prespecified Sponsor and CRO personnel 
will be unblinded for the IA of immunogenicity, safety, and efficacy. 
The purpose of the unblinding is to enable the group to develop regulatory submission 
documents and to address questions from regulatory agencies during the regulatory review of the 
submission. After unblinding, this unblinded team will not participate in the conduct or 
execution of the subsequent course of the study. The study Data Blinding Plan provides details of 
the blinding/unblinding process and personnel. The study site staff, investigators, study monitors, 
and participants will remain blinded until the initiation of Part 1B or Part 1C or Part 2. 
8.1.1. 
Breaking the Blind  
A participant or participants may be unblinded in the event of an SAE or other severe event, or if 
there is a medical emergency requiring the identity of the product to be known to properly treat a 
participant. If a participant becomes seriously ill or pregnant during the study, the blind will be 
broken if knowledge of the administered vaccine will affect that participant’s dosing options. In 
the event of a medical emergency requiring identification of the vaccine administered to an 
individual participant, the investigator will make every attempt to contact the Sponsor medical 
lead to explain the need for opening the code within 24 hours of opening the code. The 
investigator will be responsible for documenting the time, date, reason for the code break, and 
the names of the personnel involved. 
In addition to the aforementioned situations where the blind may be broken, the data will also be 
unblinded to a statistical team at specified timepoints for IA as outlined in Section 8.7.1. 
8.2. 
Statistical Hypothesis  
8.2.1. 
Part 1  
8.2.1.1. 
Part 1A  
If an accepted serum Ab threshold of protection against COVID-19 is established for the primary 
immunogenicity objective, the null hypothesis is that the percentage of participants on 
mRNA-1273 with serum Ab equal to or above the established threshold at Day 57 is ≤ 70% (ie, 
H0: percentage of participants on mRNA-1273 ≤ 70% with serum Ab at Day 57 equal to or 
above the established threshold). 
The study would be considered as meeting the immunogenicity objective if the 95% CI of 
percentage of participants on mRNA-1273 rules out 70% (lower bound of the 95% CI > 70%). 
If an accepted serum Ab threshold of protection against COVID-19 is not available for the 
primary immunogenicity objective, the immunogenicity analysis of primary vaccine response 
will be performed using the noninferiority tests of the 2 null hypotheses based on the 2 
coprimary endpoints, respectively. 
Coprimary endpoint 1: Ab GM value at Day 57 
The null hypothesis H10: immunogenicity response to mRNA-1273 as measured by Ab GM 
value at Day 57 is inferior in adolescents (12 to < 18 years of age) compared with that in young 
adults (18 to 25 years of age) using mRNA-1273 Study P301 data. 

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The noninferiority in Ab GM in adolescents compared with that in young adults (18 to 25 years 
of age) is demonstrated by that the lower bound of the 95% CI of the GMR rules out 0.667 
(lower bound >0.667) using a noninferiority margin of 1.5. The GMR is the ratio of the GM 
value of adolescents on mRNA-1273 in this study, Study P203, at Day 57 compared with the 
GM value of young adults (18 to 25 years of age) on mRNA-1273 in Study P301. 
Coprimary endpoint 2: Ab SRR at Day 57 
A definition of seroresponse will be provided in the SAP based on forthcoming information 
about assay performance. 
The null hypothesis H20: immunogenicity response to mRNA-1273 as measured by SRR at 
Day 57 is inferior in adolescents (12 to < 18 years of age) compared with that in young adults 
(18 to 25 years of age) using mRNA-1273 Study P301 data. 
The noninferiority in SRR in adolescents compared with that in young adults (18 to 25 years of 
age) is demonstrated by that the lower bound of the 95% CI of the SRR difference rules 
out -10% (ie, lower bound >-10%) using the noninferiority margin of 10%. The SRR difference 
is defined as the rate in adolescents receiving mRNA-1273 minus the rate in young adults (18 to 
25 years of age) receiving mRNA-1273 from Study P301. 
The study would be considered as meeting the primary immunogenicity objective if 
noninferiority is demonstrated based on both coprimary endpoints. 
Details regarding the assay to be used to assess noninferiority will be provided in the SAP. 
8.2.1.2. 
Part 1C–1 – Homologous Booster Phase  
The immunogenicity analysis of BD vaccine response against the ancestral strain will be 
performed using the noninferiority tests of the 2 null hypotheses based on the 2 coprimary 
endpoints, respectively. 
Coprimary Endpoint 1: Ab GM value at BD-Day 29 
Null hypothesis H10: immunogenicity response to mRNA-1273 BD as measured by Ab GM 
value at BD-Day 29 in adolescents (12-<18 years of age) in Study P203 Part 1C-1 is inferior 
compared with Ab GM value at Day 57 (28 days after Dose 2) in the primary series of 
mRNA-1273 in young adults (18 to 25 years of age) in Study P301. 
The noninferiority in Ab GM value at BD-Day 29 in Study P203 Part 1C-1 compared with Ab 
GM value at Day 57 in the primary series in young adults (18 to 25 years of age) in Study P301 
will be demonstrated by the GMR 95% CI lower bound >0.667 using a noninferiority margin of 
1.5. The GMR is defined as the GM value of Ab at BD-D29 in Study P203 Part 1C-1 compared 
with Ab GM value at Day 57 (28 days after Dose 2) following the primary series of mRNA-1273 
in Study P301. 
Coprimary Endpoint 2: Ab Seroresponse Rate (SRR) at BD-Day 29 
Null hypothesis H20: immunogenicity response to mRNA-1273 BD as measured by SRR at 
BD-Day 29 in adolescents (12-<18 years of age) in Study P203 Part 1C-1 is inferior compared 
with SRR at Day 57 (28 days after Dose 2) following the primary series of mRNA-1273 in 
young adults (18 to 25 years of age) in Study P301. 

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The noninferiority in SRR at BD-D29 compared with SRR at Day 57 (28 days after Dose 2) 
following the primary series of mRNA-1273 will be demonstrated by the SRR difference 95% CI 
lower bound >-10% using the noninferiority margin of 10%. The SRR difference is defined as 
the SRR at BD-Day 29 Study P203 Part 1C-1 minus the rate at Day 57 (28 days after Dose 2) 
following the primary series of mRNA-1273 in young adults in Study P301. Seroresponse is 
defined as Ab value change from baseline (preDose 1) below the LLOQ to ≥4 × LLOQ, or at 
least a 4-fold rise if baseline is ≥ LLOQ. 
The primary immunogenicity objective in Part 1C-1 is met if the noninferiority is demonstrated 
based on both coprimary endpoints. 
Key Secondary Endpoint 1: GM value of Ab Against Circulating Strain at BD-Day 29 
Null hypothesis H10: immunogenicity response to mRNA-1273 BD as measured by GM value of 
Ab against circulating strain at BD-Day 29 in adolescents (12-<18 years of age) in Study P203 
Part 1C-1 is inferior compared with GM value of Ab against circulating strain at Day 57 (28 days 
after Dose 2) in the primary series of mRNA-1273 in young adults (18 to 25 years of age) in 
Study P301. 
The noninferiority in Ab GM value at BD-Day 29 in Study P203 Part 1C-1 compared with Ab 
GM value at Day 57 in the primary series in young adults (18 to 25 years of age) in Study P301 
will be demonstrated by the GMR 95% CI lower bound >0.667 using a noninferiority margin of 
1.5. The GMR is defined as the ratio of GM value of Ab at BD-Day 29 in Study P203 Part 1C-1 
compared with Ab GM value at Day 57 (28 days after Dose 2) following the primary series of 
mRNA-1273 in Study P301. 
Key Secondary Endpoint 2: Seroresponse Rate (SRR) of Ab Against Circulating Strain at 
BD-Day 29 
Null hypothesis H20: immunogenicity response to mRNA-1273 BD as measured by SRR of Ab 
against circulating strain at BD-Day 29 in adolescents (12-<18 years of age) in Study P203 
Part 1C-1 is inferior compared with SRR of Ab against circulating strain at Day 57 (28 days after 
Dose 2) following the primary series of mRNA-1273 in young adults (18 to 25 years of age) in 
Study P301. 
The noninferiority in SRR at BD-D29 compared with SRR at Day 57 (28 days after Dose 2) 
following the primary series of mRNA-1273 will be demonstrated by the SRR difference 95% CI 
lower bound >-10% using the noninferiority margin of 10%. The SRR difference is defined as 
the SRR at BD-Day 29 Study P203 Part 1C-1 minus the rate at Day 57 (28 days after Dose 2) 
following the primary series of mRNA-1273 in young adults in Study P301. Seroresponse is 
defined as Ab value change from baseline (pre Dose 1) below the LLOQ to ≥4 × LLOQ, or at 
least a 4-fold rise if baseline is ≥ LLOQ. 
The key secondary immunogenicity objective in Part 1C-1 is met if the noninferiority is 
demonstrated based on both key secondary endpoints. 
8.2.2. 
Part 2  
There will be no hypothesis testing in Part 2, given that the enrollment in Part 2 was discontinued 
(Section 8.3.2). All analyses for Part 2 will be descriptive based on available data. 

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8.2.3. 
Part 3  
Hypothesis testing for the endpoints that infer effectiveness of the 50-µg mRNA-1273.222 in 
adolescents will be performed on the null hypotheses for the 2 coprimary endpoints as follows: 
Coprimary Endpoint 1: Post Dose 1 Ab GM value against Omicron BA.4/BA.5 at Day 29 
(superiority testing) 
The null hypothesis H0: GM value of Ab against Omicron BA.4/BA.5 at Day 29 post Dose 1 of 
50 μg mRNA-1273.222 in adolescents who are baseline SARS-CoV-2 positive is not superior to 
GM value at Day 57 post Dose 2 of 100 μg mRNA-1273 in baseline SARS-CoV-2 negative 
young adults (18 to 25 years of age) in Study P301.  
The superiority in Ab GM value against Omicron BA.4/BA.5 in adolescents who are baseline 
SARS-CoV-2 positive compared with that in baseline SARS-CoV-2 negative young adults (18 to 
25 years of age) is demonstrated by meeting the following success criterion: 
• The lower bound of the 95% CI of the GMR >1. 
The GMR is the ratio of the GM value against Omicron BA.4/BA.5 at Day 29 post Dose 1 of 
50 μg mRNA-1273.222 in adolescents who are baseline SARS-CoV-2 positive in Study P203 
Part 3 over the GM value against Omicron BA.4/BA.5 at Day 57 in baseline SARS-CoV-2 
negative young adults (18 to 25 years of age) post Dose 2 of 100 μg mRNA-1273 in Study P301. 
Coprimary Endpoint 2: Post Dose 1 Ab GM value against the ancestral strain at Day 29 
(noninferiority testing) 
The null hypothesis H0: GM value of Ab against ancestral strain at Day 29 post Dose 1 of 50 μg 
mRNA-1273.222 in adolescents who are baseline SARS-CoV-2 positive is inferior to GM value 
at Day 57 post Dose 2 of 100 μg mRNA-1273 in baseline SARS-CoV-2 negative young adults 
(18 to 25 years of age) in Study P301.  
The noninferiority in Ab GM value against ancestral strain adolescents who are baseline 
SARS-CoV-2 positive compared with that in baseline SARS-CoV-2 negative young adults (18 to 
25 years of age) is demonstrated by meeting the following success criterion: 
• The lower bound of the 95% CI of the GMR >0.667. 
The GMR is the ratio of the GM value against ancestral strain at Day 29 post Dose 1 of 50 μg 
mRNA-1273.222 in adolescents who are baseline SARS-CoV-2 positive in Study P203 Part 3 
over the GM value against ancestral strain at Day 57 in baseline SARS-CoV-2 negative young 
adults (18 to 25 years of age) post Dose 2 of 100 μg mRNA-1273 in Study P301. 
8.3. 
Power and Sample Size  
8.3.1. 
Part 1  
8.3.1.1. 
Part 1A  
The sample size of this study is driven by safety. Approximately 3000 participants will be 
randomly assigned in a 2:1 ratio to receive mRNA-1273 and placebo (Section 5.2). With 
2000 participants exposed to mRNA‑1273, the study has at least 90% probability to observe at 
least 1 participant with an AE at a true 0.25% AE rate. 

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Serum samples from all participants will be collected and banked, a subset of participants will be 
selected, and their samples will be processed for immunogenicity testing (the Immunogenicity 
Subset). 
Approximately 362 participants who receive mRNA-1273 will be selected for the 
Immunogenicity Subset, with a target of 289 participants receiving mRNA-1273 in the PP 
Immunogenicity Subset (adjusting for approximately 20% of participants who may be excluded 
from the PP Immunogenicity Subset, as they may not have immunogenicity results due to any 
reason). The sample size of the Immunogenicity Subset may be updated with data from other 
mRNA-1273 studies or external data especially regarding a threshold of protection. In such a 
situation, the final sample size of the Immunogenicity Subset will be documented in the SAP. 
For the primary immunogenicity objective, with approximately 289 participants in the PP 
Immunogenicity Subset, the study will have > 90% power to rule out 70% with a 2-sided 95% CI 
for the percentage of mRNA-1273 participants exceeding the acceptable threshold if the true rate 
of participants exceeding the acceptable threshold is 80%. 
If an acceptable Ab threshold of protection against COVID-19 is not available at the time of 
analysis, for the primary immunogenicity objective, noninferiority tests of 2 null hypotheses 
based on 2 coprimary endpoints, respectively, will be performed. The sample size calculation for 
each of the 2 noninferiority tests was performed, and the larger sample size was chosen for the 
study. 
• With approximately 289 participants in the PP Immunogenicity Subset in Study P203 
and 289 participants in the PP Immunogenicity Subset in young adults (18 to 25 years 
of age) from Study P301, there will be 90% power to demonstrate noninferiority of 
the immune response as measured by Ab GM value in adolescents in Study P203 at a 
2-sided α of 0.05, compared with that in young adults (18 to 25 years of age) from 
Study P301 receiving mRNA-1273, assuming an underlying GMR value of 1 and a 
noninferiority margin of 1.5. The SD of the log‑transformed levels is assumed to be 
1.5. 
• With approximately 289 participants in the PP Immunogenicity Subset in Study P203 
and 289 participants in the PP Immunogenicity Subset in young adults (18 to 25 years 
of age) from Study P301, there will be at least 90% power to demonstrate 
noninferiority of the immune response as measured by the SRR in adolescents in 
Study P203 at a 2-sided α of 0.05, compared with that in young adults (18 to 25 years 
of age) from Study P301 receiving mRNA-1273, assuming a true SRR of 85% in 
young adults (18 to 25 years of age) from Study P301, and a true SRR of 85% in 
adolescents in Study P203 (ie, true rate difference is 0 compared to young adults from 
Study P301), and a noninferiority margin of 10%. 
8.3.1.2. 
Part 1C  
8.3.1.2.1. Part 1C-1– Homologous Booster Phase  
All participants enrolled in Part 1A or Part 1B who meet the eligibility criteria for BD will be 
offered a BD of mRNA-1273 50 µg. With more than 1,000 participants expected to receive 

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mRNA‑1273 BD, the study Part 1C-1 has a 90% probability to observe at least 1 participant with 
an AE at a true AE rate of 0.25%. 
Serum samples from all participants will be collected and banked, a subset of participants will be 
selected (as described in the SAP document version 4.0), and their samples will be processed for 
immunogenicity testing (the Immunogenicity Subset) at specified timepoints. 
Approximately 400 participants who receive mRNA-1273 BD will be selected for the 
Immunogenicity Subset for Part 1C-1, with a target of 289 participants receiving mRNA-1273 
BD in the PP Immunogenicity Subset with prebooster negative SARS-CoV-2 for Part 1C-1 
(adjusting for approximately 25% of participants who may be excluded as they may have 
prebooster positive SARS-CoV-2, have no immunogenicity results due to any reason or have 
protocol deviations impacting critical data). 
For the primary immunogenicity objective in Part 1C-1, noninferiority tests of 2 null hypotheses 
based on 2 coprimary endpoints, respectively, will be performed. 
• With approximately 289 participants receiving mRNA-1273 BD in the PP 
Immunogenicity Subset with prebooster negative SARS-CoV-2 in Study P203 
Part 1C-1 and 289 participants in the PP Immunogenicity Subset in young adults (18 
to 25 years of age) in Study P301, there will be 90% power to demonstrate 
noninferiority of the immune response post BD as measured by Ab GM value in 
adolescents in Study P203 Part 1C-1 compared with Ab GM value in young adults 
(18 to 25 years of age) following primary series of mRNA-1273 in Study P301, at a 
2-sided α of 0.05, assuming an underlying GMR value of 1 and a noninferiority 
margin of 1.5. The SD of the log‑transformed levels is assumed to be 1.5. 
• With approximately 289 participants receiving mRNA-1273 BD in the PP 
Immunogenicity Subset with prebooster negative SARS-CoV-2 in Study P203 
Part 1C-1 and 289 participants in the PP Immunogenicity Subset in young adults (18 
to 25 years of age) in Study P301, there will be at least 90% power to demonstrate 
noninferiority of the immune response post BD as measured by SRR in adolescents in 
Study P203 Part 1C-1 compared with SRR in young adults of (18 to 25 years of age) 
following primary series of mRNA-1273 in Study P301, at a 2-sided α of 0.05, 
assuming true SRR of 90% in young adults (18 to 25 years of age) following primary 
series of mRNA-1273 in Study P301, and a true SRR of 90% post BD in adolescents 
in Study P203 Part 1C-1 (ie, true rate difference is 0 compared to young adults [18 to 
25 years of age] from Study P301), and a noninferiority margin of 10%. 
8.3.1.2.2. Part 1C-2 – Heterologous Booster Phase  
Approximately 362 participants who received non-Moderna COVID-19 vaccine as primary 
series vaccination at least 3 months prior were planned to be enrolled to receive mRNA-1273 
50 µg as heterologous booster in Part 1C-2. However, the study population in Part 1C-2 will 
have less than the planned number of participants enrolled, as a result of slow enrollment and 
discontinuation of recruitment in Part 1C-2 (Section 3.1.1.4). 

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8.3.2. 
Part 2  
Approximately 362 participants were planned to be enrolled to receive mRNA-1273 50 µg in the 
open-label Part 2. However, the study population in Part 2 will have less than the planned 
number of participants receiving at least one dose of 50 µg mRNA-1273, with a small sample 
size as a result of slow enrollment and discontinuation of recruitment in Part 2 (Section 3.1.2). 
8.3.3. 
Part 3  
With at least 300 adolescents enrolled in Part 3 to receive 50 µg mRNA-1273.222, the study will 
have at least a 95% probability to observe at least 1 participant with an AE at a true AE rate of 
1%.  
Assuming a true serum Ab GMR of 1.6 for GM value against Omicron BA.4/BA.5 at Day 29 
after Dose 1 of mRNA-1273.222 in baseline SARS-CoV-2 positive adolescents compared with 
GM value against Omicron BA.4/BA.5 at Day 57 after Dose 2 of mRNA-1273 primary series in 
young adults who are baseline SARS-CoV-2 negative in P301, with approximately 
168 participants in the PP Immunogenicity Subset who are baseline SARS-CoV-2 positive in 
P203 Part 3 and 300 young adults in P301 who are baseline SARS-CoV-2 negative, there will be 
at least >90% power to demonstrate superiority of the serum Ab GM value against Omicron 
BA.4/BA.5 after Dose 1 of mRNA-1273.222 in adolescents in P203 to that after Dose 2 of 
mRNA-1273 in young adults in Study P301 at two-sided α of 0.05 using a superiority margin of 
1.0. The standard deviation of the natural log transformed levels of Ab is assumed to be 1.5.  
Assuming a true serum Ab GMR of 1.1 for GM value against ancestral strain at Day 29 after 
Dose 1 of mRNA-1273.222 in baseline SARS-CoV-2 positive adolescents compared with GM 
value against ancestral strain at Day 57 after Dose 2 of mRNA-1273 primary series in young 
adults who are baseline SARS-CoV-2 negative in P301, this sample size will also provide at least 
>90% power to demonstrate noninferiority of GM value of Ab against ancestral strain at Day 29 
post Dose 1 of mRNA-1273.222 in adolescents in P203 to that after Dose 2 of mRNA-1273 in 
young adults in Study P301 at two-sided α of 0.05 using a noninferiority margin of 1.5. The 
standard deviation of the natural log transformed levels of Ab is assumed to be 1.5. 
With approximately 30% of participants in Part 3 who may be excluded from the PP 
Immunogenicity Subset-baseline SARS-CoV-2 positive (PPIS-POS), as they may be baseline 
SARS-CoV-2 negative or have missing immunogenicity results due to any reason or protocol 
deviations impacting critical data, approximately 240 participants are required in Part 3 to 
provide 168 participants in the PP Immunogenicity Subset-baseline SARS-CoV-2 positive. 
8.4. 
Analysis Sets  
The analysis sets are defined in Table 7. 

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Table 7: 
Analysis Sets  
Analysis Set 
Description 
Randomization Set 
All participants who are randomized, regardless of the participants’ treatment 
status in the study. 
FAS 
All randomized participants who received at least 1 injection of IP. 
Immunogenicity Subset 
A subset of participants in the FAS will be selected for immunogenicity testing. 
PP Immunogenicity Subset 
A subset of participants in the FAS will be selected for immunogenicity testing. 
The PP Immunogenicity Subset includes participants selected for the 
Immunogenicity Subset who received planned doses of study vaccination per 
schedule, complied with immunogenicity testing schedule, and have no major 
protocol deviations that impact key or critical data. Participants who are 
seropositive at baseline will be excluded from the PP Immunogenicity Subset. 
The PP Immunogenicity Subset will be used for analyses of immunogenicity 
unless specified otherwise. 
PP Set for Efficacy 
All participants in the FAS who received planned doses of study vaccination, 
had no immunologic or virologic evidence of prior COVID-19, and have no 
major protocol deviations that impact key or critical efficacy data. 
Solicited Safety Set 
The Solicited Safety Set consists of FAS participants who contributed any 
solicited AR data. 
The Solicited Safety Set will be used for the analyses of solicited ARs. 
Safety Set 
All randomized participants who receive at least 1 dose of IP. The Safety Set 
will be used for all analyses of safety except for the solicited ARs.  
mITT Set 
All participants in the FAS who have no serologic or virologic evidence of prior 
SARS-CoV-2 infection before the first dose of IP (both negative RT-PCR test 
for SARS-CoV-2 and negative serology test based on bAb specific to 
SARS-CoV-2 nucleocapsid) at baseline. 
mITT1 Set 
All participants in the mITT Set excluding those who received the wrong 
treatment (ie, at least 1 dose received is not as randomized or planned). 
PP Immunogenicity Subset for 
BD phase 
The PP Immunogenicity Subset for BD phase includes participants who 
received planned BD per schedule, complied with immunogenicity testing 
schedule, and have no major protocol deviations that impact key or critical data, 
with prebooster negative or positive SARS-CoV-2. The PP Immunogenicity 
Subset with prebooster negative SARS-CoV-2 will be used for the primary 
immunogenicity analysis. 
PP Immunogenicity Subset for 
Part 3 
The PP Immunogenicity Subset for Part 3 includes participants who received 
planned dose per schedule, complied with immunogenicity testing schedule, and 
have no major protocol deviations that impact key or critical data, with baseline 
negative or positive SARS-CoV-2. The PP Immunogenicity Subset for Part 3 
with baseline-positive SARS-CoV-2 status will serve as the population for the 
primary and secondary analysis of immunogenicity data at Day 29 in Part 3.  
Abbreviations: AR = adverse reaction; bAb = binding antibody; COVID-19 = coronavirus disease 2019; FAS = full 
analysis set; IP = investigational product; mITT = modified intent-to-treat; PP = per-protocol; RT-PCR = reverse 
transcription polymerase chain reaction; SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2.  
Note: Positive SARS-CoV-2 status at baseline is defined as a positive RT-PCR test for SARS-CoV-2, and/or a 
positive serology test based on bAb specific to SARS-CoV-2 nucleocapsid (as measured by Roche Elecsys 
Anti-SARS-CoV-2 assay) on or before Day 1. Negative status is defined as a negative RT-PCR test for 
SARS-CoV-2, and a negative serology test based on bAb specific to SARS-CoV-2 nucleocapsid (as measured by 
Roche Elecsys Anti-SARS-CoV-2 assay) on or before Day 1. 

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8.5. 
Statistical Methods  
Data from Part 1A, Part 1B, and Part 1C will be presented separately as applicable. 
8.5.1. 
Baseline Characteristics and Demographics  
Demographic variables (eg, age, race, sex, height, weight, and BMI) and baseline characteristics 
will be summarized by treatment group. Summary statistics (mean, SD for continuous variables, 
and number and percentage for categorical variables) will be provided. 
8.5.2. 
Safety Analyses  
All safety analyses will be based on the Safety Set, except summaries of solicited ARs, which 
will be based on the Solicited Safety Set. All safety analyses will be provided by treatment 
group. 
Safety and reactogenicity will be assessed by clinical review of all relevant parameters including 
solicited ARs (local and systemic events), unsolicited AEs, SAEs, MAAEs, AESI, AEs leading 
to discontinuation, vital sign measurements, and physical examination findings. 
The number and percentage of participants with any solicited local AR, with any solicited 
systemic AR, and with any solicited AR during the 7-day follow-up period after each injection 
(except Part 1B) will be summarized. 
The number and percentage of participants with any solicited local AR, with any solicited 
systemic AR, and with any solicited AR during the 7-day follow-up period after each dose 
(except Part 1B) will be provided. A 2-sided 95% exact CI using the Clopper-Pearson method 
will also be provided for the percentage of participants with any solicited AR. 
The number and percentage of participants with unsolicited AEs, SAEs, MAAEs, Grade 3 or 
higher ARs and AEs, and AEs leading to discontinuation from IP or withdrawal from the study 
will be summarized. Unsolicited AEs will be presented by MedDRA preferred term and system 
organ class. 
The number of events of solicited ARs, unsolicited AEs/SAEs, and MAAEs will be reported in 
summary tables accordingly. 
For all other safety parameters, descriptive summary statistics will be provided, and Table 8 
summarizes analysis strategy for safety parameters. Further details will be described in the SAP. 
Table 8: 
Analysis Strategy for Safety Parameters  
Safety Endpoint 
Number and Percentage of Participants, 
Number of Events 
95% CI 
Any solicited AR (overall and by local, systemic) 
X 
X 
Any unsolicited AE 
X 
— 
Any SAE 
X 
— 
Any AESI 
X 
__ 
Any unsolicited MAAE 
X 
— 
Any unsolicited treatment-related AE 
X 
— 

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Safety Endpoint 
Number and Percentage of Participants, 
Number of Events 
95% CI 
Any treatment-related SAE 
X 
— 
Discontinuation from dosing/withdrawal from 
study participation due to AE 
X 
— 
Any severe AE 
X 
— 
Any treatment-related severe AE 
X 
— 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; 
CI = confidence interval; MAAE = medically attended adverse event; PT = preferred term; SAE = serious adverse 
event; SOC = system organ class. 
Notes: 95% CI using the Clopper-Pearson method, X = results will be provided. Unsolicited AEs will be 
summarized by SOC and PT coded by MedDRA. 
8.5.3. 
Immunogenicity Analyses in Part 1  
The SAP will describe the complete set of immunogenicity analyses, including the approach to 
sample participants into an Immunogenicity Subset for analysis of immunogenicity. The PP 
Immunogenicity Subset is the primary analysis set for immunogenicity unless otherwise 
specified. The primary immunogenicity objective of this study is to use the immunogenicity 
response to infer efficacy in adolescents (12 to <18 years in this study). The primary 
immunogenicity analysis is performed in Part 1A. 
If an accepted serum Ab threshold of protection against COVID-19 is available based on data 
from other mRNA-1273 studies or external data, the number and percentage of participants with 
Ab greater than or equal to the threshold at Day 57 will be provided with a 2-sided 95% CI using 
the Clopper-Pearson method. If the lower bound of the 95% CI on the mRNA-1273 group is 
>70%, the primary immunogenicity objective of this study will be considered to be met. 
The percentage of participants with serum Ab greater than or equal to the threshold with 95% CI 
will be provided at each postbaseline timepoint. The CI will be calculated using the 
Clopper-Pearson method. 
If an accepted serum Ab threshold of protection against COVID-19 is not established, the 
noninferiority of primary vaccine response as measured by Ab GM value and SRR in adolescents 
compared with those in young adults (18 to 25 years of age) receiving mRNA-1273 will be 
assessed. The study is considered as meeting the primary immunogenicity objective if the 
noninferiority of the immune response to mRNA-1273 as measured by both GM value and SRR 
at Day 57 is demonstrated in adolescents in this study at a 2-sided α of 0.05, compared with that 
in young adults (18 to 25 years of age) in Study P301 receiving mRNA-1273. 
An ANCOVA model will be carried out with Ab value at Day 57 as a dependent variable and a 
group variable (adolescents in Study P203 and young adults in Study P301) as the fixed variable. 
The GM values of the adolescents at Day 57 will be estimated by the GLSM from the model. 
The GMR (ratio of GM values) will be estimated by the ratio of GLSM from the model. A 
corresponding 2-sided 95% CI will be provided to assess the difference in immune response for 
the adolescents in Study P203 compared to the young adults (18 to 25 years of age) in Study 
P301 at Day 57. The noninferiority of immune response to mRNA-1273 as measured by GM 
value will be considered demonstrated if the lower bound of the 95% CI of the GMR is >0.667 
based on the noninferiority margin of 1.5. 

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The number and percentage (rate) of participants achieving Ab seroresponse at Day 57 will be 
summarized. The difference of SRRs between adolescents receiving mRNA-1273 in Study P203 
and young adults (18 to 25 years of age) receiving mRNA-1273 in Study P301 will be calculated 
with 95% CI. The noninferiority in SRR of adolescents in Study P203 compared to young adults 
(18 to 25 years of age) in Study P301 will be considered demonstrated if the lower bound of the 
95% CI of the SRR difference is >-10%, based on the noninferiority margin of 10%. 
In addition, the GM level of specific nAb and bAb with corresponding 95% CI will be provided 
at each timepoint. The 95% CIs will be calculated based on the t-distribution of the log 
transformed values then back transformed to the original scale. The GMFR of nAb and bAb with 
corresponding 95% CI will be provided at each timepoint with Day 57 as the primary timepoint 
of interest. Descriptive summary statistics including median, minimum, and maximum will also 
be provided. 
8.5.4. 
Efficacy Analyses  
To evaluate the incidence of COVID-19 after vaccination with mRNA-1273 or placebo, the 
incidence rate will be provided by vaccination group, calculated as the number of cases divided 
by the total person-time. The incidence rate ratio of mRNA-1273 versus placebo may be 
provided with its 95% CI computed using the exact method conditional upon the total number of 
cases adjusted by the total person-time. 
For SARS-CoV-2 infection (serologically confirmed SARS-CoV-2 infection or COVID-19), 
regardless of symptomatology or severity, infection rate will be provided by vaccination group. 
The infection rate ratio of mRNA-1273 versus placebo may be provided with its 95% CI using 
the exact method conditional upon the total number of cases adjusted by the total person-time. 
The incidence rate of asymptomatic SARS-CoV-2 infection will also be provided. 
The secondary efficacy analyses will be performed in the PP set, with sensitivity analyses in the 
FAS, mITT Set, and mITT1 Set. 
8.5.5. 
Long-term Analysis (Including Part 1B)  
Long-term analysis will be performed including data collected in the Open-label Observational 
Phase (Part 1B), and prior to BD if a BD is received. The analysis will include participants who 
are randomized to mRNA-1273 in Part 1A and remained in the study with or without unblinding, 
and participants who are originally randomized to placebo and later crossed over to receive 
mRNA-1273 in Part 1B after unblinding. Long-term analysis of applicable safety, efficacy, and 
immunogenicity endpoints will be summarized descriptively by treatment cohort as defined in 
Table 9 without treatment group comparison. 
In the long-term safety analysis, unsolicited AEs (SAE, AESI, MAAE, and AE leading to 
discontinuation) and deaths will be summarized. 
In the long-term immunogenicity analysis, nAb and bAb values will be summarized at specified 
timepoints. 
In the long-term efficacy analysis, the incidence rates of COVID-19 and of SARS-CoV-2 
infection cases will be counted starting 14 days after the second dose of IP for participants in 
treatment cohort of mRNA-1273 or starting 14 days after the second dose of mRNA-1273 for 
participants in the Placebo-mRNA-1273 cohort. Incidence rate with 95% CI adjusting for 

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person-time will be provided. The incidence rate of asymptomatic SARS-CoV-2 infection will 
also be provided. 
Table 9: 
Treatment Cohorts for the Long-term Analysis  
Long-term Treatment Cohort 
Description 
mRNA-1273 
Participants randomized to mRNA-1273 in the Blinded Phase  
Placebo-mRNA-1273 
Participants randomized to Placebo in the Blinded Phase who crossed over to 
mRNA-1273 in the Open-label Observational Phase 
8.5.6. 
Booster Phase Analysis  
8.5.6.1. 
Part 1C-1 – Homologous Booster Phase  
Booster Phase analysis will be performed in participants who receive a BD in Part 1C-1. Safety, 
immunogenicity endpoints, and incidence of COVID-19 and SARS-CoV-2 infection will be 
summarized descriptively, and by prebooster SARS-CoV-2 status if applicable. 
In the Booster Phase safety analysis, the number and percentage of participants with unsolicited 
AEs, severe AEs, treatment-related AEs, SAEs, MAAEs, AESIs, and AEs leading to 
discontinuation from the study participation in Part 1C-1 will be summarized. 
The number and percentage of participants with any solicited local AR, with any solicited 
systemic AR, and with any solicited AR during the 7-day follow-up period after the BD will be 
provided. 
In the Part 1C-1 Booster Phase, for the coprimary endpoints (Ab GM value and SRR against the 
ancestral strain) and key secondary endpoints (Ab GM value and SRR against the circulating 
strain), the following analyses will be performed for the respective hypothesis testing: 
• The GM titers with 95% CI will be summarized using t-distribution of the log 
transferred values and then back transformed to the original scale. The GMR with 
95% CI to compare postbooster GM value at BD-Day 29 in adolescents in 
Study P203 with the primary series GM value at Day 57 (28 days after Dose 2) in 
young adults (18 to 25 years of age) in Study P301 will be computed based on the 
t-distribution of mean difference in the log transferred values and then back 
transformed to the original scale. 
• The SRR with 95% CI (using Clopper-Pearson method) will be summarized. The 
SRR difference with 95% CI (using Miettinen-Nurminen score method) to compare 
postbooster SRR at BD-Day 29 in adolescents in Study P203 with the primary series 
SRR at Day 57 (28 days after Dose 2) in young adults in Study P301 will be 
computed. Seroresponse is defined as Ab value change from baseline (pre Dose 1) 
below the LLOQ to ≥4 × LLOQ, or at least a 4-fold rise if baseline is ≥LLOQ. 
In the Booster Phase immunogenicity analyses, the GM titers or levels for specific nAb and bAb, 
with corresponding 95% CI will be provided at BD-Day 1, BD-Day 29, BD-Day 181, and 
BD-Day 361 (Part 1C-1). GMFR relative to pre Dose 1, (Homologous Booster) BD-Day 1 and 
prior Day 57 in the phase of primary 2-dose series of mRNA-1273 will be summarized with 95% 
CIs at BD-Day 29, BD-Day 181, and BD-Day 361 (Part 1C-1). The 95% CIs will be calculated 

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based on the t-distribution of the log transformed values then back transformed to the original 
scale. Descriptive summary statistics including median, minimum, and maximum will also be 
provided. The immunogenicity descriptive summaries will be provided in the participants who 
have available nAb and bAb assay results for the specified timepoints. 
In the Booster Phase, the incidence rate of the first occurrence of symptomatic COVID-19 
starting 14 days after the BD will be summarized by prebooster SARS-CoV-2 status. The 
incidence rate of SARS-CoV-2 infection (symptomatic or asymptomatic infection) starting 
14 days after the BD, and the incidence rate of asymptomatic SARS-CoV-2 infection starting 
14 days after the BD will be summarized. The incidence rates with 95% CI will be computed 
adjusting for person-years starting from BD-Day 1 in Part 1C-1. 
8.5.6.2. 
Part 1C-2 – Heterologous Booster Phase Analysis  
Heterologous Booster Phase analysis will be performed in participants who receive mRNA-1273 
50 µg in Part 1C-2. Safety, immunogenicity endpoints, and incidence of COVID-19 and 
SARS-CoV-2 infection will be summarized descriptively, and by prebooster SARS-CoV-2 status 
if applicable. 
In the Heterologous Booster Phase safety analysis, the number and percentage of participants 
with unsolicited AEs, severe AEs, treatment-related AEs, SAEs, MAAEs, AESIs, and AEs 
leading to discontinuation from the study participation in Part 1C-2 will be summarized. 
The number and percentage of participants with any solicited local AR, with any solicited 
systemic AR, and with any solicited AR during the 7-day follow-up period after the BD will be 
provided. 
In the Heterologous Booster Phase immunogenicity analyses, the GM titers or levels for specific 
nAb and bAb (against the ancestral strain or against specific circulating variants of concern), 
with corresponding 95% CI will be provided at BD-Day 1, BD-Day 29, BD-Day 181, and 
BD-Day 361. Geometric mean fold rise relative to BD-Day 1 will be summarized with 95% CIs 
at BD-Day 29, BD-Day 181, and BD-Day 361. The 95% CIs will be calculated based on the 
t-distribution of the log transformed values then back transformed to the original scale. 
Descriptive summary statistics including median, minimum, and maximum will also be provided 
for GM value and GMFR. The SRR and category of at least 2-fold rise relative to BD-Day 1 will 
be summarized with numbers and percentages of participants. The immunogenicity descriptive 
summaries will be provided in the PP Immunogenicity Subset who have available nAb and bAb 
assay results for the specified timepoints. 
In the Heterologous Booster Phase, the incidence rate of the first occurrence of symptomatic 
COVID-19 starting 14 days after the BD will be summarized by prebooster SARS-CoV-2 status. 
The incidence rate of SARS-CoV-2 infection (symptomatic or asymptomatic infection) starting 
14 days after the BD, and the incidence rate of asymptomatic SARS-CoV-2 infection starting 
14 days after the BD will be summarized. The incidence rates with 95% CI will be computed 
adjusting for person-years starting from BD-Day 1 in Part 1C-2. 
8.5.7. 
Part 2 Analysis  
Part 2 safety and immunogenicity endpoints will be summarized descriptively. 

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In the safety analysis, the number and percentage of participants with unsolicited AEs, severe 
AEs, treatment-related AEs, SAEs, MAAEs, AESIs, and AEs leading to discontinuation from the 
study participation in Part 2 will be summarized. 
The number and percentage of participants with any solicited local AR, with any solicited 
systemic AR, and with any solicited AR during the 7-day follow-up period after each injection 
will be provided. 
In the immunogenicity descriptive analyses, the GM value for specific Ab (against the ancestral 
strain or against specific circulating variants of concern) with corresponding 95% CI, and GMFR 
from baseline with 95% CI will be provided by timepoint. GM and GMFR 95% CIs will be 
calculated based on the t-distribution of the log transformed values then back transformed to the 
original scale. Descriptive summary statistics including median, minimum, and maximum will 
also be provided for GM and GMFR. The SRR and category of at least 2-fold rise from baseline 
by timepoint will be summarized with numbers and percentages of participants. The 
immunogenicity descriptive summaries will be provided in the PP Immunogenicity Subset who 
have available nAb and bAb assay results for the specified timepoints. 
8.5.8. 
Part 3 Analysis  
In the safety analysis, the number and percentage of participants with unsolicited AEs, severe 
AEs, treatment-related AEs, SAEs, MAAEs, AESIs, and AEs leading to discontinuation from the 
study participation in Part 3 will be summarized. 
The number and percentage of participants with any solicited local AR, with any solicited 
systemic AR, and with any solicited AR during the 7-day follow-up period after each injection 
will be provided. 
In the Part 3 immunogenicity analysis, for the coprimary endpoints (Ab GM value against 
Omicron BA.4/BA.5 and the ancestral strain at Day 29 after Dose 1 of 50 µg mRNA-1273.222 in 
baseline SARS-CoV-2 positive adolescents in Study P203 compared with those at Day 57 after 
Dose 2 of 100 µg mRNA-1273 in baseline SARS-CoV-2 negative adults 18 to 25 years of age in 
Study P301), the following analyses will be performed for the respective hypothesis testing: 
An ANCOVA model will be carried out with Ab value at Day 29 in P203 and Ab value at 
Day 57 in P301 as a dependent variable and a group variable (baseline SARS-CoV-2 positive 
adolescents in Study P203 and baseline negative SARS-CoV-2 young adults in Study P301) as 
the fixed variable, where a covariate may be included in the model (to be specified in the SAP). 
The GM value at Day 29 in P203 and the GM value at Day 57 in P301, and respective GMR for 
P203 compared to P301 will be estimated from the model. A corresponding 2-sided 95% CI of 
GMR estimated from the ANCOVA model will be provided to assess the difference in immune 
response after Dose 1 (Day 29) for the adolescents in Study P203 compared to that after Dose 2 
(Day 57) in the young adults (18 to 25 years of age) in Study P301. 
The first coprimary endpoint, superiority of immune response to mRNA-1273.222 against 
Omicron BA.4/BA.5 after Dose 1 compared to mRNA-1273 against Omicron BA.4/BA.5 after 
Dose 2 as measured by GM value will be considered demonstrated if the respective GMR 
95% CI lower bound is >1 based on a superiority margin of 1. 
The second coprimary endpoint, noninferiority of immune response to mRNA-1273.222 against 
ancestral strain after Dose 1 compared to mRNA-1273 against the ancestral strain after Dose 2 as 

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measured by GM value will be considered demonstrated if the respective GMR 95% CI lower 
bound is >0.667 based on the noninferiority margin of 1.5. The GM value and GMR with 
specified CIs will also be summarized using t-distribution of the log transferred values and then 
back transformed to the original scale, and by baseline SARS-CoV-2 status. 
Secondary endpoints evaluating SRR with 95% CIs (using Clopper-Pearson method) will be 
summarized by baseline SARS-CoV-2 status at Day 29 in adolescents in Study P203, and at 
Day 57 in adults in Study P301. Seroresponse at subject level is defined as Ab value change from 
baseline (preDose 1) below the LLOQ to ≥4 × LLOQ, or at least a 4-fold rise if baseline is 
≥LLOQ. The SRR and category of at least 2-fold rise from baseline by timepoint will be 
summarized with numbers and percentages of participants. 
The GM values for specific nAb and bAb, with corresponding 95% CIs, and GMFR from 
baseline with 95% CIs will be summarized by timepoint. The 95% CIs will be calculated based 
on the t-distribution of the log transformed values then back transformed to the original scale. 
Descriptive summary statistics including median, minimum, and maximum will also be 
provided.  
The incidence rate of the first occurrence of symptomatic COVID-19 14 days after Dose 1 will 
be summarized. The incidence rates with 95% CIs will be computed adjusting for person-years. 
8.5.9. 
Exploratory Analyses  
Exploratory analyses will be described in the SAP before database lock. 
8.5.10. 
Subgroup Analyses  
Subgroup analyses will be performed as described in the SAP. 
8.6. 
Multiplicity Adjustment  
A hierarchical sequential hypothesis testing (fixed-sequence) method will be used to adjust 
multiplicity to preserve the family-wise type I error rate (α = 0.05). The hypothesis testing for the 
2 coprimary endpoints (GMT and SRR) for the primary series of mRNA-1273 in Part 1A was 
completed and statistically significant based on data snapshot dated 08 May 2021, and thus the α 
level of 0.05 can be passed to Part 1C-1 hypothesis testing. In Part 1C-1 Homologous Booster 
Phase, the hypothesis testing for the 2 coprimary endpoints (GMT and SRR against the ancestral 
strain) after BD of mRNA-1273 will be tested at α level of 0.05. The testing in Part 1A and 1C-1 
will continue through the sequence only until an endpoint is not statistically significant (did not 
meet specified noninferiority success criteria), in which case the testing will stop. If the 
hypothesis testing for the 2 coprimary endpoints in Part 1C-1-Homologous Booster Phase is 
statistically significant (meeting the noninferiority success criteria of the coprimary endpoints), 
the α level of 0.05 will be passed to the hypothesis testing in Part 3. 
For the key secondary objective in Part 1C-1 Homologous Booster Phase to evaluate immune 
response elicited by the 50 µg prototype booster of mRNA-1273 against variant(s) of interest, the 
key secondary endpoints will be analyzed independently, given that prototype vaccine 
mRNA-1273 does not contain variant specific sequences. 

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Part 3 
Since the hypothesis testing for the coprimary endpoints in Part 1C-1 was statistically significant 
based on an IA with a data cutoff dated 16 May 2022, the α level of 0.05 (two-sided) was passed 
to Part 3 hypothesis testing.  
8.7. 
Study Analyses  
8.7.1. 
Interim Analyses  
More than one IA may be performed. 
• The IA of immunogenicity, safety, and efficacy will be performed after Day 57 
immunogenicity data are available for the Immunogenicity Subset and at least 
1500 participants (1,000 participants receiving mRNA-1273) have completed Day 57 
(1 month after Dose 2, Part 1A). This IA will be considered the primary analysis of 
immunogenicity for Part 1A. 
• An IA of immunogenicity and safety may be performed after all or subset of 
participants who receive BD have completed BD-Day 29 after the BD in Part 1C-1. 
• An IA of immunogenicity and safety may be performed after all or subset of 
participants who receive heterologous BD have completed BD-Day 29 after the BD in 
Part 1C-2. 
• An IA of immunogenicity and safety may be performed after Day 57 immunogenicity 
data are available after all or a subset of participants in Part 2 have completed Day 57 
(1 month after Dose 2, Part 2). 
• An IA of immunogenicity and safety may be performed after all or a subset of 
participants who receive 50 µg mRNA-1273.222 dose have completed Day 29 
(1 month after Dose 1). 
• At the Sponsor’s discretion, a CSR may be developed for an IA. 
8.7.2. 
Final Analysis  
The final analysis of all applicable endpoints will be performed after all participants have 
completed all planned study procedures. Results of this analysis will be presented in a final CSR, 
including individual listings. 
Additional information about all study analyses may be provided in the SAP. 

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10. 
SUPPORTING DOCUMENTATION AND OPERATIONAL 
CONSIDERATIONS  

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10.1. 
APPENDIX 1: Schedule of Assessments  
The schedules of assessments are presented in Table 10 for Part 1A, Table 12 for Part 1B, 
Table 13 for Part 1C-1, Table 14 for Part 1C-2, Table 15 for Part 2 participants who receive the 
booster dose, Table 16 for Part 2 participants who do not receive the booster dose, Table 17 for 
Part 3 participants who receive Dose 2, and Table 18 for Part 3 participants who receive a single 
dose. 
If a participant cannot attend a study site visit (scheduled or unscheduled) with the exception of 
Screening or Day 1, a home visit is acceptable if performed by appropriately delegated study site 
staff or a home healthcare service provided by the Sponsor (Section 7). If neither a participant 
visit to the study site nor a home visit to the participant is possible (with the aforementioned 
exceptions), a safety telephone call should be performed that includes the assessments scheduled 
for the safety telephone calls. 
After the Participant Decision Clinic Visit, participants will continue to follow the Part 1A SoA 
(Table 10) or Part 1B SoA (Table 12), as described in Section 3.1.1.2 and as shown in Figure 10. 
All eligible participants will be offered a BD and those who choose to receive BD will follow 
Part 1C-1 SoA (Table 13). Eligible participants that completed their primary COVID-19 
vaccination series under EUA and choose to receive a BD will follow Part 1C-2 SoA (Table 14). 
Eligible participants enrolled in Part 2 will follow Part 2 SoA (Table 15 and Table 16). Eligible 
participants enrolled in Part 3 will follow Part 3 SoA (Table 17 and Table 18). 

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Table 10: 
Schedule of Assessments Part 1A, the Blinded Phase; Part 1B Open-label Observational Phase for Participants 
who Received mRNA-1273 in Part 1A  
Visit Number 
0 
1 
2 
3 
4 
5 
- 
6 
- 
7 
Type of Visit 
C 
C 
Virtual 
Call 
C 
Virtual 
Call 
C 
SFU 
C 
SFU 
C 
Month Timepoint 
 
M0 
 
M1 
 
M2 
eDiary 
SC 
M7 
eDiary 
SC 
M13 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D82 
D293 
D362, 3 
D572, 3 
Every 4 weeks  
D71 – D1833, 4 
Every 4 weeks  
D85– D1973, 5 
D209/ Participant 
Decision Visit 3,6 
Every 4 weeks 
D223– D3633, 4 
Every 4 weeks 
D237– D3773, 5 
D3943 
Window Allowance (Days) 
- 28 
 
+ 3 
+ 7 
+ 3 
+ 7 
±3 
± 3 
- 56/+ 56 
± 3 
± 3 
± 14 
Days Since Most Recent 
Injection 
- 
0 
7 
28/0 
7 
28 
- 
- 
180 
- 
- 
365 
Informed consent/assent form, 
demographics, concomitant 
medications, medical history  
X 
 
 
 
 
 
 
 
 
 
 
 
Revised informed 
consent/assent form 
 
 
 
 
 
 
 
 
X 
 
 
 
Review of inclusion and 
exclusion criteria 
X 
X 
 
 
 
 
 
 
 
 
 
 
Physical examination 
including vital signs, height, 
weight7 
X 
X 
 
X 
  
X 
 
 
X 
 
 
X 
Pregnancy test8 
X 
X 
 
X 
 
 
 
 
 
 
 
 
Randomization 
 
X 
 
 
 
 
 
 
 
 
 
 
Study injection (including 
30-minute post dose 
observation period) 
 
X 
 
X 
 
 
 
 
 
 
 
 

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Visit Number 
0 
1 
2 
3 
4 
5 
- 
6 
- 
7 
Type of Visit 
C 
C 
Virtual 
Call 
C 
Virtual 
Call 
C 
SFU 
C 
SFU 
C 
Month Timepoint 
 
M0 
 
M1 
 
M2 
eDiary 
SC 
M7 
eDiary 
SC 
M13 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D82 
D293 
D362, 3 
D572, 3 
Every 4 weeks  
D71 – D1833, 4 
Every 4 weeks  
D85– D1973, 5 
D209/ Participant 
Decision Visit 3,6 
Every 4 weeks 
D223– D3633, 4 
Every 4 weeks 
D237– D3773, 5 
D3943 
Window Allowance (Days) 
- 28 
 
+ 3 
+ 7 
+ 3 
+ 7 
±3 
± 3 
- 56/+ 56 
± 3 
± 3 
± 14 
Days Since Most Recent 
Injection 
- 
0 
7 
28/0 
7 
28 
- 
- 
180 
- 
- 
365 
Blood sample for vaccine 
immunogenicity9 
 
X 
 
 
 
X 
 
 
X 
 
 
X 
Nasopharyngeal or nasal swab 
sample for SARS-CoV-210 
 
X 
 
X 
 
X 
 
 
X 
 
 
 
Surveillance for COVID-19/ 
Illness visit11/ Unscheduled 
visit 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Convalescent Visit12 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
eDiary activation for recording 
solicited ARs (7 days)13 
 
X 
 
X 
 
 
 
 
 
 
 
 
Review of eDiary data 
 
 
X 
 
X 
 
 
 
 
 
 
 
Follow-up safety telephone 
calls14 
 
 
 
 
 
 
 
X 
 
X 
 
 
Recording of unsolicited AEs 
 
X 
X 
X 
X 
X 
 
 
 
 
 
 
Recording of MAAEs and 
concomitant medications 
relevant to or for the treatment 
of the MAAE15 
 
X 
X 
X 
X 
X 
X 
 
X 
X 
 
X 

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Visit Number 
0 
1 
2 
3 
4 
5 
- 
6 
- 
7 
Type of Visit 
C 
C 
Virtual 
Call 
C 
Virtual 
Call 
C 
SFU 
C 
SFU 
C 
Month Timepoint 
 
M0 
 
M1 
 
M2 
eDiary 
SC 
M7 
eDiary 
SC 
M13 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D82 
D293 
D362, 3 
D572, 3 
Every 4 weeks  
D71 – D1833, 4 
Every 4 weeks  
D85– D1973, 5 
D209/ Participant 
Decision Visit 3,6 
Every 4 weeks 
D223– D3633, 4 
Every 4 weeks 
D237– D3773, 5 
D3943 
Window Allowance (Days) 
- 28 
 
+ 3 
+ 7 
+ 3 
+ 7 
±3 
± 3 
- 56/+ 56 
± 3 
± 3 
± 14 
Days Since Most Recent 
Injection 
- 
0 
7 
28/0 
7 
28 
- 
- 
180 
- 
- 
365 
Recording of SAEs and 
concomitant medications 
relevant to or for the treatment 
of the SAE15 
 
X 
X 
X 
X 
X 
X 
 
X 
X 
 
X 
Recording of AESI  
 
X 
X 
X 
X 
X 
X 
 
X 
X 
 
X 
Recording of concomitant 
medications and nonstudy 
vaccinations15 
 
X 
X 
X 
X 
X 
 
 
 
 
 
 
Study completion 
 
 
 
 
 
 
 
 
 
 
 
X 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; BMI = body mass index; C = clinic visit; COVID-19 = coronavirus disease 
2019; D = day; eDiary = electronic diary; FDA = USA Food and Drug Administration; IP = investigational product; IRB = institutional review board; LAR = legally acceptable 
representative; M = month; MAAE = medically attended AE; NP = nasopharyngeal; SC = safety (telephone) call; SFU = safety follow-up; RT-PCR = reverse transcriptase 
polymerase chain reaction; SAE = serious adverse event; SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2. 
Note: In accordance with FDA Guidance on Conduct of Clinical Trials of Medical Products during COVID-19 Public Health Emergency (DHHS 2020), investigators may convert 
study site visits to home visits or telemedicine visits with the approval of the Sponsor. 
Note: If during the Participant Decision Visit (Table 11) the participant is unblinded and determined to have received 2 doses of mRNA-1273 in Part 1A, due to statistical 
considerations, they will be considered in the Open-label Observational Phase but will continue to follow the Part 1A SoA. 
1. 
Day 0 and Day 1 may be combined on the same day. Additionally, the Day 0 Visit may be performed over multiple visits if preformed within the 28-day Screening window. 
2. 
All scheduled study visits should be completed within the respective visit windows. If the participant is not able to attend a study site visit due to the COVID-19 pandemic 
(self-quarantine or disruption of study site activities following business continuity plans and/or local government mandates for “stay at home” or “shelter in place”), a safety 
telephone call to the participant should be made in place of the study site visit. The safety telephone call should encompass all scheduled visit assessments that can be 
completed remotely, such as assessment for AEs and concomitant medications (eg, as defined in scheduled safety telephone calls). Home visits will be permitted for all 

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nondosing visits, except for Screening, if a participant cannot visit the study site due to the COVID-19 pandemic. Home visits must be permitted by the study site IRB and the 
participant via informed consent/assent and have prior approval from the Sponsor (or its designee). 
3. 
If the visit for the second dose (Day 29) is disrupted and cannot be completed at Day 29 +7 days due to the COVID-19 pandemic (self-quarantine or disruption of study site 
activities following business continuity plans and/or local government mandates for “stay at home” or “shelter in place”), the visit window may be extended to 
Day 29 + 21 days. When the extended visit window is used, the remaining study visits should be rescheduled to follow the inter-visit interval from the actual date of the 
second dose. 
4. 
Safety follow-up via an eDiary questionnaire will be performed every 4 weeks from Day 71 to Day 183 and again from Day 223 to Day 363. 
5. 
Safety follow-up via a safety telephone call will be performed every 4 weeks from Day 85 to Day 197 and again from Day 237 to Day 377. 
6. 
The Participant Decision Visit may be performed over multiple visits. Once the Participant Decision Visit has been initiated, all assessments must be completed within a 7-
day period. 
7. 
Physical examination: A full physical examination, including height and weight, will be performed at Day 1, Day 29, Day 57, Day 209, and Day 394. BMI will be calculated 
only at Screening Visit (Day 0). Symptom-directed physical examinations may be performed at other timepoints at the discretion of the investigator. On each injection day 
before injection and again 7 days after injection, the arm receiving the injection should be examined and the associated lymph nodes should be evaluated. Any clinically 
significant finding identified during a study visit should be reported as a MAAE. Vital signs are to be measured predose and postdose on days of injection (Day 1 and 
Day 29). When applicable, vital signs should be measured before blood collection. Participants who are febrile (body temperature ≥ 38.0°C/100.4°F) before injection on 
Day 1 or Day 29 must have the visit rescheduled within the relevant visit window to receive the injection. Afebrile participants with minor illnesses can be enrolled at the 
discretion of the investigator. 
8. 
Pregnancy test at Screening and Day 1 and before the second study injection will be a point-of-care urine test. At the discretion of the investigator, a pregnancy test either via 
blood or point-of-care urine test can be performed at any time. 
9. 
Sample must be collected prior to dosing of injection on Day 1. 
10. 
The nasopharyngeal or nasal swab sample will be used to ascertain the presence of SARS-CoV-2 via RT-PCR. 
11. 
An unscheduled visit may be prompted by reactogenicity issues, illness visit criteria for COVID-19, or new or ongoing AEs. If a participant meets the prespecified criteria of 
suspicion for COVID-19 (Section 7.1.6), the participants will be asked to return within 72 hours or as soon as possible to the study site for an unscheduled illness visit, to 
include an NP or nasal swab sample (for RT-PCR testing) and other clinical evaluations. If a study site visit is not possible, a home visit may be arranged to collect the NP or 
nasal sample and conduct clinical evaluations. If a home visit is not possible, the participant will be asked to submit a saliva sample to the study site by a Sponsor-approved 
method. At this illness visit, the NP or nasal swab samples will be collected to evaluate for the presence of SARS-CoV-2 infection. NP or nasal swab samples will also be 
tested for the presence of other respiratory pathogens. If due to COVID-19 related restrictions in the community, the participant’s LAR performed a home test rather than 
obtaining a test performed by a health care professional, see Section 7.1.6. In addition, the study site may collect an additional NP or nasal sample for SARS-CoV-2 testing to 
be able to render appropriate medical care for the study participant as determined by local standards of care. Additionally, clinical information will be carefully collected to 
evaluate the severity of the clinical case. 
12. 
A convalescent visit will be scheduled approximately 28 days (+7 days) after diagnosis. At this visit, an NP or nasal swab sampling for viral PCR and a blood sample will be 
collected for potential immunologic assessment of SARS-CoV-2 infection. 
13. 
Diary entries will be recorded by the participant at approximately 30 minutes after injection while at the study site with instruction provided by study staff. Study participants 
will continue to record entries in the eDiary each day after they leave the study site, preferably in the evening, on the day of injection and for 6 days following injection. If a 
solicited local or systemic AR continues beyond Day 7 after vaccination, the participant will be prompted to capture details of the solicited local or systemic AR in the eDiary 
until the AR is resolves or the next IP injection occurs, whichever occurs first; capture of details of ARs in the eDiary should not exceed 28 days after each vaccination. ARs 
recorded in eDiaries beyond Day 7 should be reviewed either via telephone call or at the following study visit. 
14. 
Trained study site personnel will call all participants to collect information relating to any AEs, MAAEs, SAEs, AEs leading to study withdrawal, information on concomitant 
medications associated with those events, and any nonstudy vaccinations. In addition, study personnel will collect information on known participant exposure to someone 
with known COVID-19 or SARS-CoV-2 infection and on participant experience of COVID-19 symptoms. 
15. 
All concomitant medications and nonstudy vaccinations will be recorded through 28 days after each injection; all concomitant medications relevant to or for the treatment of 
an SAE or MAAE will be recorded from Day 1 through the final visit (Day 394). 

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Table 11: 
Participant Decision Clinic Visit  
 
All Participants 
Return to clinic for Participant Decision Clinic Visit 
X 
Sign revised Informed Consent Form  
X 
Confirm participant’s choice to be unblinded or not to be unblinded  
X 
Confirm participant’s choice to receive open-label mRNA-1273 
X 
Nasopharyngeal or nasal swab  
X 
Blood for immunologic analysis 
X 
Counsel about public health measures to limit virus spread1 
X 
1. 
All participants are counseled about the importance of continuing other public health measures to limit the 
spread of disease including physical-social distancing, wearing a mask, and hand-washing. 
Figure 10: 
Schedule of Part 1A and Part 1B Participant Visits During the Part 1B 
Open-label Period 
 
 

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Table 12: 
Schedule of Assessments Part 1B, Open-label Observational Phase for 
Participants Who Previously Received Placebo  
Visit Number 
7 
8 
9 
10 
11 
Type of Visit 
C 
C 
C 
SC8 
C 
Study Visit Day  
(~D209/ 
Participant 
Decision 
Visit) 
OL-D1 
OL-D29 
OL-D572 
 
 
OL-D113 
 
 
 
OL-
D1789 
Window Allowance (Days) 
-56/+561 
-3/+7 
±14 
± 3 
±14 
Days Since Most Recent Injection 
0 
28 
28 
84 
149 
Informed consent form  
These 
assessments 
are already 
performed as 
part of the 
regular D209 
Visit. 
 
 
 
 
Blood for vaccine immunogenicity 
 
X 
 
X 
Nasopharyngeal or nasal swab sample 
for SARS-CoV-23 
X 
X 
 
 
Physical examination including vital 
signs4 
PE including 
vitals 
performed as 
part of D209 
Visit.  
X 
X 
 
X 
X 
Vitals 
obtained post 
dose. 
X 
 
 
 
Pregnancy testing 
X 
X 
 
 
 
Study injection (including 30-minute 
postdosing observation period) 
X 
X 
 
 
 
Informed consent for BD 
 
 
X7 
 
 
Recording of MAAEs and concomitant 
medications relevant to or for the 
treatment of the MAAE5 
X 
X 
X 
X 
X 
Recording of SAEs and concomitant 
medications relevant to or for the 
treatment of the SAE5 
X 
X 
X 
X 
X 
Recording of AESI  
X 
X 
X 
X 
X 
Recording of concomitant medications 
and nonstudy vaccinations5 
X 
X 
X 
X 
X 
Surveillance for COVID-19/ Illness 
visit6/ Unscheduled visit 
X 
X 
X 
X 
X 
Study completion (for Part 1B) 
 
 
 
 
X 

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Abbreviations: AE = adverse event; AESI = adverse event of special interest; BD = booster dose; C = clinic visit;  
COVID-19 = coronavirus disease 2019; D = Day; M = month; MAAE = medically attended AE; NP = nasopharyngeal; 
OL = open-label; PCR = polymerase chain reaction; RT-PCR = reverse transcriptase polymerase chain reaction; SAE = serious 
adverse events; SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2; SC = safety (telephone) call. 
1. 
The Participant Decision Visit may be performed over multiple visits. Once the Participant Decision Visit has been initiated, 
all assessments must be completed within a 7-day period. 
2. 
After the OL-D57 visit, Part 1B participants who choose to receive BD will have one additional safety call at OL-D113 prior 
to entering Part 1C-1. 
3. 
The NP or nasal swab sample, collected prior to vaccination on days of injection, will be used to ascertain the presence of 
SARS-CoV-2 via PCR. 
4. 
Physical examination: A symptom-directed physical examination will be performed at OL-D1, OL-D29, OL-D57, and 
OL-D178. Symptom-directed physical examinations may be performed at other timepoints at the discretion of the 
investigator. Any clinically significant finding identified during a study visit should be reported as a MAAE. Vital signs are 
to be collected predosing and postdosing on days of injection (OL-D1 and OL-D29). When applicable, vital sign 
measurements should be performed before blood collection. Participants who are febrile (body temperature 
≥ 38.0°C/100.4°F) before injection on OL-D1 or OL-D29 must be rescheduled within the relevant window period to receive 
the injection. Afebrile participants with minor illnesses can be administered investigational product at the discretion of the 
investigator. 
5. 
All concomitant medications and nonstudy vaccinations will be recorded throughout the study; all concomitant medications 
relevant to or for the treatment of an SAE or MAAE will be recorded from Day 1 through OL-D113 before entering Part 1C-
1. If a participant declines a BD, all concomitant medications relevant to or for the treatment of an SAE or MAAE will be 
recorded from Day 1 through OL-D178. 
6. 
If a participant meets the prespecified criteria of suspicion for COVID-19 (Section 7.1.6), the participants will be asked to 
return within 72 hours or as soon as possible to the study site for an unscheduled illness visit, to include an NP or nasal swab 
sample (for RT-PCR testing) and other clinical evaluations. If a study site visit is not possible, a home visit may be arranged 
to collect the NP or nasal sample and conduct clinical evaluations. If a home visit is not possible, the participant will be 
asked to submit a saliva sample to the study site by a Sponsor-approved method. At this illness visit, the NP or nasal swab 
samples will be collected to evaluate for the presence of SARS-CoV-2 infection. NP or nasal swab samples will also be 
tested for the presence of other respiratory pathogens. If due to COVID-19 related restrictions in the community, the 
participant’s LAR performed a home test rather than obtaining a test performed by a health care professional, see 
Section 7.1.6. In addition, the study site may collect an additional NP or nasal sample for SARS-CoV-2 testing to be able to 
render appropriate medical care for the study participant as determined by local standards of care. Additionally, clinical 
information will be carefully collected to evaluate the severity of the clinical case. 
7. 
During OL-D57, all participants will be given the option to receive a BD. Participants will choose whether to receive the BD 
or not and sign the consent form. Those who decline BD will continue with Part 1B. Those who choose to receive a BD will 
have one safety call prior to entering Part 1C-1. 
8. 
All participants in Part 1B who choose to receive BD will have one additional safety call at OL-D113 prior to entering Part 
1C-1. 
9. 
OL-D178 is only for those who decline BD. Participants who choose to receive a BD will follow Part 1C-1 SoA after the 
OL-D113 safety call. The BD-D1 has a window of -1 month, thus, can be scheduled at least 5 months after the second dose, 
and participants will need to complete the OL-D113 safety call. 

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Table 13: 
Schedule of Assessments Part 1C-1 – Homologous Booster Dose Phase  
Visit Number 
BD-1 
BD-1a 
 
BD-2 
BD-3 
 
BD-4 
Type of Visit 
C 
C 
SC11 
C 
C 
SC 
C 
Study Visit Day 
BD-D11 
(D209: 
mRNA-1273; 
D394: 
placebo-
mRNA-1273) 
BD-D4 
7, 14, and 21 
days 
after BD-D1 
(BD-D8,  
BD-D15, 
and BD-D22) 
BD-D29 
BD-D181 
(Day 390: 
mRNA-
1273; Day 
571: 
placebo-
mRNA-
1273) 
270 days 
after BD-1 
(BD-D271) 
BD-D361 
(Day 571 
mRNA-1273; 
Day 751 
placebo- 
mRNA-1273) 
Window Allowance (Days) 
-28 days  
-2 
+3 
-3/+14 
-3/+14 
+3 
-3/+14 
Days Since Most Recent 
Vaccination (in Part 1C-1) 
0 
3 
7, 14, 21 
28 
180 
270 
360 
Confirm informed consent form 
signing 
X 
 
 
 
 
 
 
Physical examination2 
X 
 
 
X 
X 
 
X 
Pregnancy testing3 
X 
 
 
 
 
 
 
Immunogenicity Assessment 
 
 
 
 
 
 
 
Blood for immunologic analysis4 
X 
 
 
X 
X 
 
X 
Biomarker Assessment 
 
 
 
 
 
 
 
Blood sample for potential 
biomarker analysis5 
 
X 
 
 
 
 
 
Dosing 
 
 
 
 
 
 
 
Study injection (including 30-minute 
postdosing observation period6) 
X 
 
 
 
 
 
 
Efficacy Assessment 
 
 
 
 
 
 
 
Surveillance for COVID-
19/Unscheduled Visit7 
X 
X 
X 
X 
X 
X 
X 
Nasal swab8 
X 
 
 
 
 
 
 
Safety Assessments 
 
 
 
 
 
 
 

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Visit Number 
BD-1 
BD-1a 
 
BD-2 
BD-3 
 
BD-4 
Type of Visit 
C 
C 
SC11 
C 
C 
SC 
C 
Study Visit Day 
BD-D11 
(D209: 
mRNA-1273; 
D394: 
placebo-
mRNA-1273) 
BD-D4 
7, 14, and 21 
days 
after BD-D1 
(BD-D8,  
BD-D15, 
and BD-D22) 
BD-D29 
BD-D181 
(Day 390: 
mRNA-
1273; Day 
571: 
placebo-
mRNA-
1273) 
270 days 
after BD-1 
(BD-D271) 
BD-D361 
(Day 571 
mRNA-1273; 
Day 751 
placebo- 
mRNA-1273) 
Window Allowance (Days) 
-28 days  
-2 
+3 
-3/+14 
-3/+14 
+3 
-3/+14 
Days Since Most Recent 
Vaccination (in Part 1C-1) 
0 
3 
7, 14, 21 
28 
180 
270 
360 
Follow-up safety9 
 
 
X 
 
 
X 
X 
eDiary activation for recording 
solicited ARs (7 days)10 
X 
 
 
 
 
 
 
Review of eDiary data10 
 
 
X10(BD-D8) 
 
 
 
 
Recording of unsolicited AEs11 
X 
X 
X 
X 
 
 
 
Recording of MAAEs and 
concomitant medications relevant to 
or for the treatment of the MAAE12 
X 
X 
X 
X 
X 
X 
X 
Recording of AE leading to 
withdrawal  
X 
X 
X 
X 
X 
X 
X 
Recording of AESIs 
X 
X 
X 
X 
X 
X 
X 
Recording of SAEs and concomitant 
medications relevant to or for the 
treatment of the SAE12 
X 
X 
X 
X 
X 
X 
X 
Recording of concomitant 
medications and nonstudy 
vaccinations 
X 
X 
X 
X 
X 
X 
X 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; BD = booster dose; C = clinic visit; D = day; 
eDiary = electronic diary; MAAE = medically attended AE; NP = nasopharyngeal; SAE = serious adverse event; SC = safety (phone) call. 

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Note: In accordance with FDA Guidance on Conduct of Clinical Trials of Medical Products during COVID-19 Public Health Emergency (DHHS 2020), 
investigators may convert study site visits to home visits or telemedicine visits with the approval of the Sponsor. 
1. 
A BD may be administered to all participants who are currently enrolled in Part 1A or Part 1B provided there are no current contraindications for further 
dosing (Section 6). A participant who is currently in the Convalescent Period may come in for a BD-1 visit and receive a BD as long they are no longer 
symptomatic, and this includes the possibility for a Convalescent Visit Day 28 to overlap and be combined with a BD-1 visit. 
2. 
Symptom-directed physical examination will be performed at the BD-Day 1. On dosing day before injection, the arm receiving the injection should be 
examined and the associated lymph nodes should be evaluated. At visits BD-2 (BD-D29), BD-3 (BD-D181) and BD-4 (BD-D361), a symptom-directed 
physical examination may be performed at the discretion of the investigator. Any clinically significant finding identified during a study visit should be 
reported as a MAAE. Vital signs are to be collected predosing and postdosing (participant will be seated for at least 5 minutes before all measurements are 
taken per Section 7.1.4) on the day of injection (BD-D1). Participants who are febrile (body temperature ≥ 38.0°C/100.4°F) before dosing (BD-D1) must be 
rescheduled to receive the injection. Afebrile participants with minor illnesses can be vaccinated at the discretion of the investigator. 
3. 
The pregnancy test at the BD-1 visit will be a point-of-care urine test. At the discretion of the investigator, a pregnancy test either via blood or point-of-care 
urine test can be performed. 
4. 
Sample should be collected prior to dosing on BD-D1. 
5. 
All participants who chose to receive a BD. Serum sample from two ~4 mL blood draws. Biomarker plasma and biomarker serum samples will be stored for 
potential future biomarker assessment. 
6. 
Postdosing, participants will have a 30-minute observation period. 
7. 
An unscheduled visit may be prompted by reactogenicity issues, illness visit criteria for COVID-19, or new or ongoing AEs. If a participant meets the 
prespecified criteria of suspicion for COVID-19 (Section 7.1.6), the participants will be asked to return within 72 hours or as soon as possible to the study 
site for an unscheduled illness visit, to include an NP or nasal swab sample (for RT-PCR testing) and other clinical evaluations. If a study site visit is not 
possible, a home visit may be arranged to collect the nasal swab sample and conduct clinical evaluations. If a home visit is not possible, the participant will 
be asked to submit a saliva sample to the study site by a Sponsor-approved method. At this illness visit, the NP or nasal swab samples will be collected to 
evaluate for the presence of SARS-CoV-2 infection. Nasal swab samples will also be tested for the presence of other respiratory pathogens. If due to 
COVID-19 related restrictions in the community, the participant’s LAR performed a home test rather than obtaining a test performed by a health care 
professional, see Section 7.1.6. In addition, the study site may collect an additional nasal swab sample for SARS-CoV-2 testing to be able to render 
appropriate medical care for the study participant as determined by local standards of care. Additionally, clinical information will be carefully collected to 
evaluate the severity of the clinical case. 
8. 
The nasal swab sample must be collected prior to injection at the BD-1 visit. 
9. 
Trained study personnel will call all participants to collect information relating to any unsolicited AEs, MAAEs (including any signs and symptoms of 
COVID-19), AESIs, AEs leading to withdrawal, SAEs, information on concomitant medications associated with those events, and any nonstudy 
vaccinations. 
10. Diary entries will be recorded by the participant at approximately 30 minutes after injection while at the study site with instruction provided by study staff. 
Study participants will continue to record entries in the eDiary each day after they leave the study site, preferably in the evening, on the day of injection and 
for 6 days following injection. If a solicited local or systemic AR continues beyond Day 7 after vaccination, the participant will be prompted to capture 
details of the solicited local or systemic AR in the eDiary until the AR resolves; capture of details of ARs in the eDiary should not exceed 28 days after 
vaccination. ARs recorded in eDiaries beyond Day 7 should be reviewed either via telephone call or at the following study visit. Review of eDiary will occur 
on BD-D8. 
11. Only for participants who chose to receive a BD. 
12. All concomitant medications relevant to or for the treatment of an SAE or MAAE will be recorded from Screening through the final visit. 

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Table 14: 
Schedule of Assessments Part 1C-2 – Heterologous Booster Phase  
Visit Number 
BD-0 
BD-1 
BD-1a 
 
BD-2 
BD-3 
 
BD-4 
Type of Visit 
C 
C 
C 
SC11 
C 
C 
SC 
C 
Study Visit Day 
BD-D01 
BD-D11 
BD-D4 
7, 14, and 
21 days 
after BD-
D1 
(BD-D8, 
BD-D15, 
BD-D22) 
BD-D29 
BD-D181 
 
270 days 
after BD-1 
(BD-D271) 
BD-D361 
 
Window Allowance (Days) 
-7 
- 
-2 
+3 
-3/+14 
-3/+14 
+3 
-3/+14 
Days Since Most Recent 
Vaccination (in Part 1C-2) 
- 
0 
3 
7, 14, 21 
28 
180 
270 
360 
Informed consent/assent form, 
demographics, concomitant 
medications, medical history 
X 
 
 
 
 
 
 
 
Physical examination including 
vital signs, height, weight 2 
X 
X 
 
 
X 
X 
 
X 
Pregnancy testing3 
X 
X 
 
 
 
 
 
 
Immunogenicity Assessment 
 
 
 
 
 
 
 
 
Blood for immunologic analysis4 
 
X 
 
 
X 
X 
 
X 
Biomarker Assessment 
 
 
 
 
 
 
 
 
Blood sample for potential 
biomarker analysis5 
 
 
X 
 
 
 
 
 
Dosing 
 
 
 
 
 
 
 
 
Study injection (including 30-
minute postdosing observation 
period6) 
 
X 
 
 
 
 
 
 

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Visit Number 
BD-0 
BD-1 
BD-1a 
 
BD-2 
BD-3 
 
BD-4 
Type of Visit 
C 
C 
C 
SC11 
C 
C 
SC 
C 
Study Visit Day 
BD-D01 
BD-D11 
BD-D4 
7, 14, and 
21 days 
after BD-
D1 
(BD-D8, 
BD-D15, 
BD-D22) 
BD-D29 
BD-D181 
 
270 days 
after BD-1 
(BD-D271) 
BD-D361 
 
Window Allowance (Days) 
-7 
- 
-2 
+3 
-3/+14 
-3/+14 
+3 
-3/+14 
Days Since Most Recent 
Vaccination (in Part 1C-2) 
- 
0 
3 
7, 14, 21 
28 
180 
270 
360 
Efficacy Assessment 
 
 
 
 
 
 
 
 
Surveillance for COVID-
19/Unscheduled Visit7 
 
X 
X 
X 
X 
X 
X 
X 
Nasal swab8 
 
X 
 
 
 
 
 
 
Safety Assessments 
 
 
 
 
 
 
 
 
Follow-up safety9 
 
 
 
X 
 
 
X 
X 
eDiary activation for recording 
solicited ARs (7 days)10 
 
X 
 
 
 
 
 
 
Review of eDiary data10 
 
 
 
X10(BD-D8) 
 
 
 
 
Recording of unsolicited AEs11 
 
X 
X 
X 
X 
 
 
 
Recording of MAAEs and 
concomitant medications 
relevant to or for the treatment of 
the MAAE12 
 
X 
X 
X 
X 
X 
X 
X 
Recording of AE leading to 
withdrawal  
 
X 
X 
X 
X 
X 
X 
X 
Recording of AESIs 
 
X 
X 
X 
X 
X 
X 
X 

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Visit Number 
BD-0 
BD-1 
BD-1a 
 
BD-2 
BD-3 
 
BD-4 
Type of Visit 
C 
C 
C 
SC11 
C 
C 
SC 
C 
Study Visit Day 
BD-D01 
BD-D11 
BD-D4 
7, 14, and 
21 days 
after BD-
D1 
(BD-D8, 
BD-D15, 
BD-D22) 
BD-D29 
BD-D181 
 
270 days 
after BD-1 
(BD-D271) 
BD-D361 
 
Window Allowance (Days) 
-7 
- 
-2 
+3 
-3/+14 
-3/+14 
+3 
-3/+14 
Days Since Most Recent 
Vaccination (in Part 1C-2) 
- 
0 
3 
7, 14, 21 
28 
180 
270 
360 
Recording of SAEs and 
concomitant medications 
relevant to or for the treatment of 
the SAE12 
 
X 
X 
X 
X 
X 
X 
X 
Recording of concomitant 
medications and nonstudy 
vaccinations 
 
X 
X 
X 
X 
X 
X 
X 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; BD = booster dose; C = clinic visit; D = day; 
eDiary = electronic diary; EUA = Emergency Use Authorization; LAR = legally acceptable representative; MAAE = medically attended AE; 
NP = nasopharyngeal; SAE = serious adverse event; SC = safety (phone) call. 
Note: In accordance with FDA Guidance on Conduct of Clinical Trials of Medical Products during COVID-19 Public Health Emergency (DHHS 2020), 
investigators may convert study site visits to home visits or telemedicine visits with the approval of the Sponsor. 
1. 
BD-Day 0 and BD-Day 1 may be combined on the same day. Additionally, the BD-Day 0 Visit may be performed over multiple visits if preformed within 
the 7-day Screening window. A BD will be administered to all eligible participants who are at least 3 months from completion of primary series under EUA 
(outside of the study). 
2. 
A full physical examination including height, weight, and vital signs will be performed at the BD-Day 1. On dosing day before injection, the arm receiving 
the injection should be examined and the associated lymph nodes should be evaluated. At visits BD-2 (BD-D29), BD-3 (BD-D181) and BD-4 (BD-D361), a 
symptom-directed physical examination may be performed at the discretion of the investigator. Any clinically significant finding identified during a study 
visit should be reported as a MAAE. Vital signs are to be collected predosing and postdosing (participant will be seated for at least 5 minutes before all 
measurements are taken per Section 7.1.4 on the day of injection (BD-D1). Participants who are febrile (body temperature ≥38.0°C/100.4°F) before dosing 
(BD-D1) must be rescheduled to receive the injection. Afebrile participants with minor illnesses can be vaccinated at the discretion of the investigator. 
3. 
The pregnancy test at the BD-1 Visit will be a point-of-care urine test. At the discretion of the investigator, a pregnancy test either via blood or point-of-care 
urine test can be performed. 

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4. 
Sample should be collected prior to dosing on BD-D1. 
5. 
Serum sample from two ~4 mL blood draws. Biomarker plasma and biomarker serum samples will be stored for potential future biomarker assessment. 
6. 
Postdosing, participants will have a 30-minute observation period. 
7. 
An unscheduled visit may be prompted by reactogenicity issues, illness visit criteria for COVID-19, or new or ongoing AEs. If a participant meets the 
prespecified criteria of suspicion for COVID-19 (Section 7.1.6), the participants will be asked to return within 72 hours or as soon as possible to the study 
site for an unscheduled illness visit, to include an NP or nasal swab sample (for RT-PCR testing) and other clinical evaluations. If a study site visit is not 
possible, a home visit may be arranged to collect the nasal swab sample and conduct clinical evaluations. If a home visit is not possible, the participant will 
be asked to submit a saliva sample to the study site by a Sponsor-approved method. At this illness visit, the NP or nasal swab samples will be collected to 
evaluate for the presence of SARS-CoV-2 infection. Nasal swab samples will also be tested for the presence of other respiratory pathogens. If due to 
COVID-19 related restrictions in the community, the participant’s LAR performed a home test rather than obtaining a test performed by a health care 
professional, see Section 7.1.6. In addition, the study site may collect an additional nasal swab sample for SARS-CoV-2 testing to be able to render 
appropriate medical care for the study participant as determined by local standards of care. Additionally, clinical information will be carefully collected to 
evaluate the severity of the clinical case. 
8. 
The nasal swab sample must be collected prior to injection at the BD-1 Visit. 
9. 
Trained study personnel will call all participants to collect information relating to any unsolicited AEs, MAAEs (including any signs and symptoms of 
COVID-19), AESIs, AEs leading to withdrawal, SAEs, information on concomitant medications associated with those events, and any nonstudy 
vaccinations. 
10. Diary entries will be recorded by the participant at approximately 30 minutes after injection while at the study site with instruction provided by study staff. 
Study participants will continue to record entries in the eDiary each day after they leave the study site, preferably in the evening, on the day of injection and 
for 6 days following injection. If a solicited local or systemic AR continues beyond Day 7 after vaccination, the participant will be prompted to capture 
details of the solicited local or systemic AR in the eDiary until the AR resolves; capture of details of ARs in the eDiary should not exceed 28 days after 
vaccination. ARs recorded in eDiaries beyond Day 7 should be reviewed either via telephone call or at the following study visit. Review of eDiary will occur 
on BD-D8. 
11. Only for participants who chose to receive a BD. 
12. All concomitant medications relevant to or for the treatment of an SAE or MAAE will be recorded from Screening through the final visit. 

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Table 15: Schedule of Assessments Part 2 (For Participants Who Receive The Booster Dose)  
Visit Number 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
- 
11 
- 
12 
Type of Visit 
C 
C 
Virtua
l Call 
C 
C 
Virtua
l Call 
C 
C 
C 
Virtua
l Call 
C 
SFU 
C 
SFU 
C 
Month Time 
Point 
 
M0 
 
M1 
 
 
M2 
M5 
 
 
 
eDiary 
SC 
M11 eDiary 
SC 
M17 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D8 
D292 
D32 
D362 
D572 
D1491 
D152 
D156 
D177 
Every 4 weeks 
D191-303 2, 3 
Every 4 weeks  
D205-317 2, 4 
D329 2 
Every 4 weeks 
D343-455 2, 3 
Every 4 weeks 
D357-469 2, 4 
D5142 
Window 
Allowance 
(Days) 
- 7 
 
+ 3 
+ 7 
-2 
+ 3 
+ 7 
-28 
-2 
+3 
+7 
±3 
± 3 
+7 
± 3 
± 3 
± 14 
Days Since Most 
Recent Injection 
- 
0 
7 
28 
3 
7 
28 
120 
3 
7 
28 
- 
- 
180 
- 
- 
365 
Informed 
consent/assent 
form, 
demographics, 
concomitant 
medications, 
medical history  
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Review of 
inclusion and 
exclusion criteria 
X 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Physical 
examination 
including vital 
signs, height, 
weight5 
X 
X 
 
X 
 
 
X 
X 
 
 
 
 
 
X 
 
 
X 
Pregnancy test6 
X 
X 
 
X 
 
 
 
X 
 
 
 
 
 
 
 
 
 

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Visit Number 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
- 
11 
- 
12 
Type of Visit 
C 
C 
Virtua
l Call 
C 
C 
Virtua
l Call 
C 
C 
C 
Virtua
l Call 
C 
SFU 
C 
SFU 
C 
Month Time 
Point 
 
M0 
 
M1 
 
 
M2 
M5 
 
 
 
eDiary 
SC 
M11 eDiary 
SC 
M17 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D8 
D292 
D32 
D362 
D572 
D1491 
D152 
D156 
D177 
Every 4 weeks 
D191-303 2, 3 
Every 4 weeks  
D205-317 2, 4 
D329 2 
Every 4 weeks 
D343-455 2, 3 
Every 4 weeks 
D357-469 2, 4 
D5142 
Window 
Allowance 
(Days) 
- 7 
 
+ 3 
+ 7 
-2 
+ 3 
+ 7 
-28 
-2 
+3 
+7 
±3 
± 3 
+7 
± 3 
± 3 
± 14 
Days Since Most 
Recent Injection 
- 
0 
7 
28 
3 
7 
28 
120 
3 
7 
28 
- 
- 
180 
- 
- 
365 
Study injection 
(including 
30-minute post-
dose observation 
period) 
 
X 
 
X 
 
 
 
X 
 
 
 
 
 
 
 
 
 
Blood sample for 
potential 
biomarker 
analysis7 
 
 
 
 
X 
 
 
 
X 
 
 
 
 
 
 
 
 
Blood sample for 
vaccine 
immunogenicity8 
 
X 
 
X 
 
 
X 
X 
 
 
X 
 
 
X 
 
 
X 
Nasal swab 
sample for SARS-
CoV-29 
 
X 
 
X 
 
 
X 
X 
 
 
 
 
 
X 
 
 
 

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Visit Number 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
- 
11 
- 
12 
Type of Visit 
C 
C 
Virtua
l Call 
C 
C 
Virtua
l Call 
C 
C 
C 
Virtua
l Call 
C 
SFU 
C 
SFU 
C 
Month Time 
Point 
 
M0 
 
M1 
 
 
M2 
M5 
 
 
 
eDiary 
SC 
M11 eDiary 
SC 
M17 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D8 
D292 
D32 
D362 
D572 
D1491 
D152 
D156 
D177 
Every 4 weeks 
D191-303 2, 3 
Every 4 weeks  
D205-317 2, 4 
D329 2 
Every 4 weeks 
D343-455 2, 3 
Every 4 weeks 
D357-469 2, 4 
D5142 
Window 
Allowance 
(Days) 
- 7 
 
+ 3 
+ 7 
-2 
+ 3 
+ 7 
-28 
-2 
+3 
+7 
±3 
± 3 
+7 
± 3 
± 3 
± 14 
Days Since Most 
Recent Injection 
- 
0 
7 
28 
3 
7 
28 
120 
3 
7 
28 
- 
- 
180 
- 
- 
365 
Surveillance for 
COVID-19/ 
Illness visit10/ 
Unscheduled visit 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Convalescent 
Visit11 
 
X 
X 
X 
X 
X 
X 
X 
X 
 
X 
X 
X 
X 
X 
X 
X 
eDiary activation 
for recording 
solicited ARs 
(7 days)12 
 
X 
 
X 
 
 
 
X 
 
 
 
 
 
 
 
 
 
Review of eDiary 
data 
 
 
X 
 
 
X 
 
 
 
X 
 
 
 
 
 
 
 
Follow-up safety 
telephone calls13 
 
 
 
 
 
 
 
 
 
 
 
 
X 
 
 
X 
 
Recording of 
unsolicited AEs 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
 
 
 
 
 
 

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Visit Number 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
- 
11 
- 
12 
Type of Visit 
C 
C 
Virtua
l Call 
C 
C 
Virtua
l Call 
C 
C 
C 
Virtua
l Call 
C 
SFU 
C 
SFU 
C 
Month Time 
Point 
 
M0 
 
M1 
 
 
M2 
M5 
 
 
 
eDiary 
SC 
M11 eDiary 
SC 
M17 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D8 
D292 
D32 
D362 
D572 
D1491 
D152 
D156 
D177 
Every 4 weeks 
D191-303 2, 3 
Every 4 weeks  
D205-317 2, 4 
D329 2 
Every 4 weeks 
D343-455 2, 3 
Every 4 weeks 
D357-469 2, 4 
D5142 
Window 
Allowance 
(Days) 
- 7 
 
+ 3 
+ 7 
-2 
+ 3 
+ 7 
-28 
-2 
+3 
+7 
±3 
± 3 
+7 
± 3 
± 3 
± 14 
Days Since Most 
Recent Injection 
- 
0 
7 
28 
3 
7 
28 
120 
3 
7 
28 
- 
- 
180 
- 
- 
365 
Recording of 
MAAEs and 
concomitant 
medications 
relevant to or for 
the treatment of 
the MAAE14 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of 
SAEs and 
concomitant 
medications 
relevant to or for 
the treatment of 
the SAE14 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of 
AESI 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 

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Visit Number 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
- 
11 
- 
12 
Type of Visit 
C 
C 
Virtua
l Call 
C 
C 
Virtua
l Call 
C 
C 
C 
Virtua
l Call 
C 
SFU 
C 
SFU 
C 
Month Time 
Point 
 
M0 
 
M1 
 
 
M2 
M5 
 
 
 
eDiary 
SC 
M11 eDiary 
SC 
M17 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D8 
D292 
D32 
D362 
D572 
D1491 
D152 
D156 
D177 
Every 4 weeks 
D191-303 2, 3 
Every 4 weeks  
D205-317 2, 4 
D329 2 
Every 4 weeks 
D343-455 2, 3 
Every 4 weeks 
D357-469 2, 4 
D5142 
Window 
Allowance 
(Days) 
- 7 
 
+ 3 
+ 7 
-2 
+ 3 
+ 7 
-28 
-2 
+3 
+7 
±3 
± 3 
+7 
± 3 
± 3 
± 14 
Days Since Most 
Recent Injection 
- 
0 
7 
28 
3 
7 
28 
120 
3 
7 
28 
- 
- 
180 
- 
- 
365 
Recording of AEs 
leading to 
withdrawal 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of 
concomitant 
medications and 
non-study 
vaccinations14 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Study completion 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
X 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; BD = booster dose; BMI = body mass index; C = clinic 
visit; COVID 19 = coronavirus disease 2019; D = day; eDiary = electronic diary; FDA = USA Food and Drug Administration; IP = investigational product; 
IRB = institutional review board; M = month; MAAE = medically attended AE; NP = nasopharyngeal; SC = safety (telephone) call; SFU = safety follow-up; 
RT-PCR = reverse transcriptase polymerase chain reaction; SAE = serious adverse event; SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2. 
Note: In accordance with FDA Guidance on Conduct of Clinical Trials of Medical Products during COVID-19 Public Health Emergency (DHHS 2020), 
investigators may convert study site visits to home visits or telemedicine visits with the approval of the Sponsor. 
Note: All scheduled study visits should be completed within the respective visit windows. If the participant is not able to attend a study site visit as a result of the 
COVID 19 pandemic (self-quarantine or disruption of study site activities following business continuity plans and/or local government mandates for “stay at 
home” or “shelter in place”), a safety telephone call to the participant should be made in place of the study site visit. The safety telephone call should 

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encompass all scheduled visit assessments that can be completed remotely, such as assessment for AEs and concomitant medications (eg, as defined in 
scheduled safety telephone calls). Home visits will be permitted for all nondosing visits, with the exception of Screening, if a participant cannot visit the 
study site as a result of the COVID-19 pandemic. Home visits must be permitted by the study site IRB and the participant via informed consent/assent and 
have prior approval from the Sponsor (or its designee). 
1. 
Day 0 and Day 1 may be combined on the same day. Additionally, the Day 0 visit may be performed over multiple visits if preformed within the 7-day 
screening window. If eligible, participants will receive 50 µg mRNA-1273 28 days apart and will receive a BD at least 3 months from second dose. 
2. 
If the visit for the second dose (Day 29) or BD (Day 149) is disrupted and cannot be completed at Day 29 +7 or at Day 149 -28 days as a result of the 
COVID-19 pandemic (self-quarantine or disruption of study site activities following business continuity plans and/or local government mandates for “stay at 
home” or “shelter in place”), the visit window may be extended to Day 29 + 21 days or Day 149 +21 days. When the extended visit window is used, the 
remaining study visits should be rescheduled to follow the inter-visit interval from the actual date of the second dose. 
3. 
Safety follow-up via an eDiary questionnaire will be performed every 4 weeks from Day 191 to Day 303 and again from Day 343 to Day 455. 
4. 
Safety follow-up via a safety telephone call will be performed every 4 weeks from Day 205 to Day 317 and again from Day 357 to Day 469.  
5. 
Physical examination: A full physical examination, including height, weight, and vital signs will be performed at Day 1, Day 29, Day 57, Day 149, Day 329, 
and Day 514. BMI will be calculated only at Screening Visit (Day 0). Symptom-directed physical examinations may be performed at other time points at the 
discretion of the investigator. On each injection day before injection and again 7 days after injection, the arm receiving the injection should be examined and 
the associated lymph nodes should be evaluated. Any clinically significant finding identified during a study visit should be reported as an MAAE. Vital signs 
are to be measured pre and post-dose on days of injection (Day 1, Day 29, and Day 149). When applicable, vital signs should be measured before blood 
collection. Participants who are febrile (body temperature ≥ 38.0°C/100.4°F) before injection on Day 1, Day 29, or Day 149 must have the visit rescheduled 
within the relevant visit window to receive the injection. Afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 
6. 
Pregnancy test at Screening and Day 1 and before the second and third/booster study injection will be a point-of-care urine test. At the discretion of the 
investigator, a pregnancy test either via blood or point-of-care urine test can be performed at any time. 
7. 
Serum sample from two ~4 mL blood draws. Biomarker plasma and biomarker serum samples will be stored for potential future biomarker assessment. 
8. 
Sample must be collected prior to dosing of injection on Day 1, Day 29, and Day 149. 
9. 
The nasal swab sample will be used to ascertain the presence of SARS-CoV-2 via RT-PCR. 
10. An unscheduled visit may be prompted by reactogenicity issues, illness visit criteria for COVID-19, or new or ongoing AEs. If a participant meets the 
prespecified criteria of suspicion for COVID-19 (Section 7.1.6), the participants will be asked to return within 72 hours or as soon as possible to the study 
site for an unscheduled illness visit, to include a nasal swab sample (for RT-PCR testing) and other clinical evaluations. If a study site visit is not possible, a 
home visit may be arranged to collect the NP or nasal sample and conduct clinical evaluations. If a home visit is not possible, the participant will be asked to 
submit a saliva sample to the study site by a Sponsor-approved method. At this illness visit, the NP or nasal swab samples will be collected to evaluate for 
the presence of SARS-CoV-2 infection. NP or nasal swab samples will also be tested for the presence of other respiratory pathogens. In addition, the study 
site may collect an additional NP or nasal sample for SARS-CoV-2 testing to be able to render appropriate medical care for the study participant as 
determined by local standards of care. Additionally, clinical information will be carefully collected to evaluate the severity of the clinical case. 
11. A convalescent visit will be scheduled approximately 28 days (+7 days) after diagnosis. At this visit, a nasal swab sampling for viral PCR and a blood 
sample will be collected for potential immunologic assessment of SARS-CoV-2 infection. 
12. Diary entries will be recorded by the participant at approximately 30 minutes after injection while at the study site with instruction provided by study staff. 
Study participants will continue to record entries in the eDiary each day after they leave the study site, preferably in the evening, on the day of injection and 
for 6 days following injection. If a solicited local or systemic AR continues beyond Day 7 after vaccination, the participant will be prompted to capture 
details of the solicited local or systemic AR in the eDiary until the AR resolves or the next IP injection occurs, whichever occurs first; capture of details of 

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ARs in the eDiary should not exceed 28 days after each vaccination. Adverse reactions recorded in eDiaries beyond Day 7 should be reviewed either via 
telephone call or at the following study visit. 
13. Trained study site personnel will call all participants to collect information relating to any AEs, MAAEs, SAEs, AEs leading to study withdrawal, 
information on concomitant medications associated with those events, and any nonstudy vaccinations. In addition, study personnel will collect information 
on known participant exposure to someone with known COVID-19 or SARS-CoV-2 infection and on participant experience of COVID-19 symptoms. 
14. All concomitant medications and nonstudy vaccinations will be recorded throughout the study; all concomitant medications relevant to or for the treatment 
of an SAE or MAAE will be recorded from Day 1 through the final visit (Day 514). 

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Table 16: 
Schedule of Assessments Part 2 (For Participants Who Do Not Receive The Booster Dose)  
Visit Number 
0 
1 
2 
3 
4 
5 
6 
7 
8 
- 
9 
- 
10 
Type of Visit 
C 
C 
Virtual 
Call 
C 
C 
Virtual 
Call 
C 
Virtual 
Call 
C 
SFU 
C 
SFU 
C 
Month Timepoint 
 
M0 
 
M1 
 
 
M2 
 
M3 
eDiary 
SC 
M7 
eDiary 
SC 
M13 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D8 
D292 
D32 
D362 
D572 
D64 
D85 
Every 4 weeks 
D99-1832, 3 
Every 4 weeks  
D113-1972, 4 
209 2 
Every 4 weeks 
D223-3072, 3 
Every 4 weeks 
D237-3212, 4 
3942 
Window Allowance 
(Days) 
- 7 
 
+ 3 
+ 7 
-2 
+ 3 
+ 7 
+3 
+7 
±3 
± 3 
+7 
± 3 
± 3 
± 14 
Days Since Most Recent 
Injection 
- 
0 
7 
28 
3 
7 
28 
35 
65 
- 
- 
180 
- 
- 
365 
Informed consent/assent 
form, demographics, 
concomitant medications, 
medical history  
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Review of inclusion and 
exclusion criteria5 
X 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
Physical examination 
including vital signs, 
height, weight6 
X 
X 
 
X 
 
 
X 
 
 
 
 
X 
 
 
X 
Pregnancy test7 
X 
X 
 
X 
 
 
 
 
 
 
 
 
 
 
 
Study injection (including 
30-minute post dose 
observation period) 
 
X 
 
X 
 
 
 
 
 
 
 
 
 
 
 
Blood sample for potential 
biomarker analysis8 
 
 
 
 
X 
 
 
 
 
 
 
 
 
 
 
Blood sample for vaccine 
immunogenicity9 
 
X 
 
X 
 
 
X 
 
X 
 
 
X 
 
 
X 

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Visit Number 
0 
1 
2 
3 
4 
5 
6 
7 
8 
- 
9 
- 
10 
Type of Visit 
C 
C 
Virtual 
Call 
C 
C 
Virtual 
Call 
C 
Virtual 
Call 
C 
SFU 
C 
SFU 
C 
Month Timepoint 
 
M0 
 
M1 
 
 
M2 
 
M3 
eDiary 
SC 
M7 
eDiary 
SC 
M13 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D8 
D292 
D32 
D362 
D572 
D64 
D85 
Every 4 weeks 
D99-1832, 3 
Every 4 weeks  
D113-1972, 4 
209 2 
Every 4 weeks 
D223-3072, 3 
Every 4 weeks 
D237-3212, 4 
3942 
Window Allowance 
(Days) 
- 7 
 
+ 3 
+ 7 
-2 
+ 3 
+ 7 
+3 
+7 
±3 
± 3 
+7 
± 3 
± 3 
± 14 
Days Since Most Recent 
Injection 
- 
0 
7 
28 
3 
7 
28 
35 
65 
- 
- 
180 
- 
- 
365 
Nasal swab sample for 
SARS-CoV-210 
 
X 
 
X 
 
 
X 
 
 
 
 
X 
 
 
 
Surveillance for 
COVID-19/ Illness visit11/ 
Unscheduled visit 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
eDiary activation for 
recording solicited ARs 
(7 days)12 
 
X 
 
X 
 
 
 
 
 
 
 
 
 
 
 
Review of eDiary data13 
 
 
X 
 
 
X 
 
 
 
 
 
 
 
 
 
Follow-up safety telephone 
calls14 
 
 
 
 
 
 
 
 
 
 
X 
 
 
X 
 
Recording of unsolicited 
AEs 
 
X 
X 
X 
X 
X 
X 
 
 
 
 
 
 
 
 
Recording of MAAEs and 
concomitant medications 
relevant to or for the 
treatment of the MAAE15 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 

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Visit Number 
0 
1 
2 
3 
4 
5 
6 
7 
8 
- 
9 
- 
10 
Type of Visit 
C 
C 
Virtual 
Call 
C 
C 
Virtual 
Call 
C 
Virtual 
Call 
C 
SFU 
C 
SFU 
C 
Month Timepoint 
 
M0 
 
M1 
 
 
M2 
 
M3 
eDiary 
SC 
M7 
eDiary 
SC 
M13 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D8 
D292 
D32 
D362 
D572 
D64 
D85 
Every 4 weeks 
D99-1832, 3 
Every 4 weeks  
D113-1972, 4 
209 2 
Every 4 weeks 
D223-3072, 3 
Every 4 weeks 
D237-3212, 4 
3942 
Window Allowance 
(Days) 
- 7 
 
+ 3 
+ 7 
-2 
+ 3 
+ 7 
+3 
+7 
±3 
± 3 
+7 
± 3 
± 3 
± 14 
Days Since Most Recent 
Injection 
- 
0 
7 
28 
3 
7 
28 
35 
65 
- 
- 
180 
- 
- 
365 
Recording of SAEs and 
concomitant medications 
relevant to or for the 
treatment of the SAE15 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of AESI 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of AEs leading 
to withdrawal 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of concomitant 
medications and nonstudy 
vaccinations15 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Study completion 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
X 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; BMI = body mass index; C = clinic visit; 
COVID-19 = coronavirus disease 2019; D = day; eDiary = electronic diary; FDA = USA Food and Drug Administration; IRB = institutional review board; 
M = month; MAAE = medically attended AE; NP = nasopharyngeal; SC = safety (telephone) call; SFU = safety follow-up; RT-PCR = reverse transcriptase 
polymerase chain reaction; SAE = serious adverse event; SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2. 
Note: In accordance with FDA Guidance on Conduct of Clinical Trials of Medical Products during COVID-19 Public Health Emergency (DHHS 2020), 
investigators may convert study site visits to home visits or telemedicine visits with the approval of the Sponsor. 
Note: All scheduled study visits should be completed within the respective visit windows. If the participant is not able to attend a study site visit due to the 
COVID-19 pandemic (self-quarantine or disruption of study site activities following business continuity plans and/or local government mandates for “stay at 
home” or “shelter in place”), a safety telephone call to the participant should be made in place of the study site visit. The safety telephone call should 

ModernaTX, Inc. 
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mRNA-1273 
Confidential 
Page 186 
encompass all scheduled visit assessments that can be completed remotely, such as assessment for AEs and concomitant medications (eg, as defined in 
scheduled safety telephone calls). Home visits will be permitted for all nondosing visits, except for Screening, if a participant cannot visit the study due to the 
COVID-19 pandemic. Home visits must be permitted by the study site IRB and the participant via informed consent/assent and have prior approval from the 
Sponsor (or its designee). 
1. 
Day 0 and Day 1 may be combined on the same day. Additionally, the Day 0 Visit may be performed over multiple visits if they occur within the 7-day 
Screening window. If eligible, participants will receive 50 µg mRNA-1273 28 days apart. 
2. 
If the visit for the second dose (Day 29) is disrupted and cannot be completed at Day 29 +7 due to the COVID-19 pandemic (self-quarantine or disruption of 
study site activities following business continuity plans and/or local government mandates for “stay at home” or “shelter in place”), the visit window may be 
extended to Day 29 + 21 days. When the extended visit window is used, the remaining study visits should be rescheduled to follow the inter-visit interval 
from the actual date of the second dose. 
3. 
Safety follow-up via an eDiary questionnaire will be performed every 4 weeks from Day 99 to Day 183 and again from Day 223 to Day 307. 
4. 
Safety follow-up via a safety telephone call will be performed every 4 weeks from Day 113 to Day 197 and again from Day 237 to Day 321. 
5. 
Review of inclusion and exclusion criteria will be conducted during Screening. However, this review may be conducted on Day 1 if Screening and Baseline 
procedures are conducted on the same day. 
6. 
Physical examination: A full physical examination, including height, weight, and vital signs will be performed at Screening, Day 1, Day 29, Day 57, Day 
209, and Day 394. BMI will be calculated only at Screening Visit (Day 0). Symptom-directed physical examinations may be performed at other timepoints at 
the discretion of the investigator. On each injection day before injection and again 7 days after injection, the arm receiving the injection should be examined 
and the associated lymph nodes should be evaluated. Any clinically significant finding identified during a study visit should be reported as a MAAE. Vital 
signs are to be measured predose and postdose on days of injection (Day 1 and Day 29). When applicable, vital signs should be measured before blood 
collection. Participants who are febrile (body temperature ≥38.0°C/100.4°F) before injection on Day 1 and Day 29 must have the visit rescheduled within the 
relevant visit window to receive the injection. Afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 
7. 
Pregnancy test at Screening and Day 1 and before the second study injection will be a point-of-care urine test. At the discretion of the investigator, a 
pregnancy test either via blood or point-of-care urine test can be performed at any time. 
8. 
Serum sample from two ~4 mL blood draws. Biomarker plasma and biomarker serum samples will be stored for potential future biomarker assessment. 
9. 
Sample must be collected prior to dosing of injection on Day 1 and Day 29. 
10. The nasal swab sample will be used to ascertain the presence of SARS-CoV-2 via RT-PCR. 
11. An unscheduled visit may be prompted by reactogenicity issues, illness visit criteria for COVID-19, or new or ongoing AEs. If a participant meets the 
prespecified criteria of suspicion for COVID-19 (Section 7.1.6), the participants will be asked to return within 72 hours or as soon as possible to the study 
site for an unscheduled illness visit, to include a nasal swab sample (for RT-PCR testing) and other clinical evaluations. If a study site visit is not possible, a 
home visit may be arranged to collect the NP or nasal sample and conduct clinical evaluations. If a home visit is not possible, the participant will be asked to 
submit a saliva sample to the study site by a Sponsor-approved method. At this illness visit, the NP or nasal swab samples will be collected to evaluate for 
the presence of SARS-CoV-2 infection. NP or nasal swab samples will also be tested for the presence of other respiratory pathogens. In addition, the study 
site may collect an additional NP or nasal sample for SARS-CoV-2 testing to be able to render appropriate medical care for the study participant as 
determined by local standards of care. Additionally, clinical information will be carefully collected to evaluate the severity of the clinical case. 
12. Diary entries will be recorded by the participant at approximately 30 minutes after injection while at the study site with instruction provided by study staff. 
Study participants will continue to record entries in the eDiary each day after they leave the study site, preferably in the evening, on the day of injection and 
for 6 days following injection. If a solicited local or systemic AR continues beyond Day 7 after vaccination, the participant will be prompted to capture 
details of the solicited local or systemic AR in the eDiary until the AR resolves or the next IP injection occurs, whichever occurs first; capture of details of 
ARs in the eDiary should not exceed 28 days after each vaccination. 
13. ARs recorded in eDiaries beyond Day 7 after vaccination should be reviewed either via telephone call or at the following study visit. 

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14. Trained study site personnel will call all participants to collect information relating to any AEs, MAAEs, SAEs, AEs leading to study withdrawal, 
information on concomitant medications associated with those events, and any nonstudy vaccinations. In addition, study personnel will collect information 
on known participant exposure to someone with known COVID-19 or SARS-CoV-2 infection and on participant experience of COVID-19 symptoms. 
15. All concomitant medications and nonstudy vaccinations will be recorded throughout the study; all concomitant medications relevant to or for the treatment 
of an SAE or MAAE will be recorded from Day 1 through the final visit (Day 394). 

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Table 17: 
Schedule of Assessments Part 3 (For Participants Who Receive Dose 2)  
Visit Number 
0 
1 
2 
3 
4 
5 
6 
- 
7 
8 
9 
10 
Type of Visit 
C 
C 
C 
Virtual 
Call 
C 
C 
C 
SFU 
C 
C 
Virtual 
Call 
C 
Month Timepoint 
 
M0 
 
 
M1 
M2 
M3 
SC 
M6 
 
 
M7 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D3 
D8 
D29 
D57 
D85 
Every 6 weeks 
D99-1412 
D1813 
D184 
D188 
D209 
Window Allowance (Days) 
- 7 
 
-2 
+ 3 
+ 7 
+3 
+7 
±3 
+ 7 
-2 
+ 3 
+ 7 
Days Since Most Recent Injection 
- 
0 
3 
7 
28 
56 
84 
- 
180/0 
3 
7 
28 
Informed consent/assent form, demographics, concomitant 
medications, medical history  
X 
 
 
 
 
 
 
 
 
 
 
 
Review of inclusion and exclusion criteria4 
X 
X 
 
 
 
 
 
 
 
 
 
 
Physical examination including vital signs, height, weight5 
X 
X 
 
 
X 
 
 
 
X 
 
 
X 
Pregnancy test6 
X 
X 
 
 
 
 
 
 
X 
 
 
 
Study injection (including 30-minute post dose observation 
period) 
 
X 
 
 
 
 
 
 
X 
 
 
 
Blood sample for potential biomarker analysis7 
 
 
X 
 
 
 
 
 
 
X 
 
 
Blood sample for vaccine immunogenicity8 
 
X 
 
 
X 
 
X 
 
X 
 
 
X 
Nasal swab sample for SARS-CoV-29 
 
X 
 
 
X 
 
X 
 
X 
 
 
X 
Surveillance for COVID-19/ Illness visit10/ Unscheduled visit 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
eDiary activation for recording solicited ARs (7 days)11 
 
X 
 
 
 
 
 
 
X 
 
 
 
Review of eDiary data12 
 
 
 
X 
 
 
 
 
 
 
X 
 
Follow-up safety telephone calls13 
 
 
 
 
 
 
 
X 
 
 
 
 
Recording of unsolicited AEs 
 
X 
X 
X 
X 
 
 
 
X 
X 
X 
X 
Recording of MAAEs and concomitant medications relevant to 
or for the treatment of the MAAE14 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 

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Visit Number 
0 
1 
2 
3 
4 
5 
6 
- 
7 
8 
9 
10 
Type of Visit 
C 
C 
C 
Virtual 
Call 
C 
C 
C 
SFU 
C 
C 
Virtual 
Call 
C 
Month Timepoint 
 
M0 
 
 
M1 
M2 
M3 
SC 
M6 
 
 
M7 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D3 
D8 
D29 
D57 
D85 
Every 6 weeks 
D99-1412 
D1813 
D184 
D188 
D209 
Window Allowance (Days) 
- 7 
 
-2 
+ 3 
+ 7 
+3 
+7 
±3 
+ 7 
-2 
+ 3 
+ 7 
Days Since Most Recent Injection 
- 
0 
3 
7 
28 
56 
84 
- 
180/0 
3 
7 
28 
Recording of SAEs and concomitant medications relevant to or 
for the treatment of the SAE14 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of AESI 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of AEs leading to withdrawal 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of concomitant medications and nonstudy 
vaccinations14 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Study completion 
 
 
 
 
 
 
 
 
 
 
 
X 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; BMI = body mass index; C = clinic visit; 
COVID-19 = coronavirus disease 2019; D = day; eDiary = electronic diary; FDA = USA Food and Drug Administration; IP = investigational product; 
IRB = institutional review board; M = month; MAAE = medically attended AE; NP = nasopharyngeal; SC = safety (telephone) call; SFU = safety follow-up; 
RT-PCR = reverse transcriptase polymerase chain reaction; SAE = serious adverse event; SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2. 
Note: In accordance with FDA Guidance on Conduct of Clinical Trials of Medical Products during COVID-19 Public Health Emergency (DHHS 2020), 
investigators may convert study site visits to home visits or telemedicine visits with the approval of the Sponsor. 
Note: All scheduled study visits should be completed within the respective visit windows. If the participant is not able to attend a study site visit due to the 
COVID-19 pandemic (self-quarantine or disruption of study site activities following business continuity plans and/or local government mandates for “stay at 
home” or “shelter in place”), a safety telephone call to the participant should be made in place of the study site visit. The safety telephone call should 
encompass all scheduled visit assessments that can be completed remotely, such as assessment for AEs and concomitant medications (eg, as defined in 
scheduled safety telephone calls). Home visits will be permitted for all nondosing visits, except for Screening, if a participant cannot visit the study site due to 
the COVID-19 pandemic. Home visits must be permitted by the study site IRB and the participant via informed consent/assent and have prior approval from 
the Sponsor (or its designee). 
1. 
Day 0 and Day 1 may be combined on the same day. Additionally, the Day 0 Visit may be performed over multiple visits if they occur within the 7-day 
Screening window. 
2. 
Safety follow-up via a safety telephone call will be performed every 6 weeks from Day 99 to Day 141. 

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3. 
If the visit for the second dose (Day 181) is disrupted and cannot be completed at Day 181 +7 due to the COVID-19 pandemic (self-quarantine or disruption 
of study site activities following business continuity plans and/or local government mandates for “stay at home” or “shelter in place”), the visit window may 
be extended to Day 181 +21 days. When the extended visit window is used, the remaining study visits should be rescheduled to follow the inter-visit interval 
from the actual date of the second dose. 
4. 
Review of inclusion and exclusion criteria will be conducted during Screening. However, this review will be conducted on Day 1 if Screening and Baseline 
procedures are conducted on the same day. 
5. 
Physical examination: A full physical examination, including height, weight, and vital signs will be performed at Screening, Day 1, Day 29, Day 181, and 
Day 209. BMI will be calculated only at Screening Visit (Day 0). Symptom-directed physical examinations may be performed at other timepoints at the 
discretion of the investigator. On each injection day before injection and again 7 days after injection, the arm receiving the injection should be examined and 
the associated lymph nodes should be evaluated. Any clinically significant finding identified during a study visit should be reported as a MAAE. Vital signs 
are to be measured predose and postdose on days of injection (Day 1 and Day 181). When applicable, vital signs should be measured before blood collection. 
Participants who are febrile (body temperature ≥38.0°C/100.4°F) before injection on Day 1 and Day 181 must have the visit rescheduled within the relevant 
visit window to receive the injection. Afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 
6. 
Pregnancy test at Screening and Day 1 and before the second study injection (Day 181) will be a point-of-care urine test. At the discretion of the investigator, 
a pregnancy test either via blood or point-of-care urine test can be performed at any time. 
7. 
Serum and plasma samples from two ~4 mL blood draws. Biomarker plasma and biomarker serum samples will be stored for potential future biomarker 
assessment. 
8. 
Sample must be collected prior to dosing of injection on Day 1 and Day 181. 
9. 
The nasal swab sample will be used to ascertain the presence of SARS-CoV-2 via RT-PCR. 
10. An unscheduled visit may be prompted by reactogenicity issues, illness visit criteria for COVID-19, or new or ongoing AEs. If a participant meets the 
prespecified criteria of suspicion for COVID-19 (Section 7.1.6), the participants will be asked to return within 72 hours or as soon as possible to the study 
site for an unscheduled illness visit, to include a nasal swab sample (for RT-PCR testing) and other clinical evaluations. If a study site visit is not possible, a 
home visit may be arranged to collect the NP or nasal sample and conduct clinical evaluations. If a home visit is not possible, the participant will be asked to 
submit a saliva sample to the study site by a Sponsor-approved method. At this illness visit, the NP or nasal swab samples will be collected to evaluate for 
the presence of SARS-CoV-2 infection. NP or nasal swab samples will also be tested for the presence of other respiratory pathogens. In addition, the study 
site may collect an additional NP or nasal sample for SARS-CoV-2 testing to be able to render appropriate medical care for the study participant as 
determined by local standards of care. Additionally, clinical information will be carefully collected to evaluate the severity of the clinical case. 
11. Diary entries will be recorded by the participant at approximately 30 minutes after injection while at the study site with instruction provided by study staff. 
Study participants will continue to record entries in the eDiary each day after they leave the study site, preferably in the evening, on the day of injection and 
for 6 days following injection. If a solicited local or systemic AR continues beyond Day 7 after vaccination, the participant will be prompted to capture 
details of the solicited local or systemic AR in the eDiary until the AR resolves or the next IP injection occurs, whichever occurs first; capture of details of 
ARs in the eDiary should not exceed 28 days after each vaccination. 
12. ARs recorded in eDiaries beyond Day 7 after vaccination should be reviewed either via telephone call or at the following study visit. 
13. Trained study site personnel will call all participants to collect information relating to any AEs, MAAEs, SAEs, AEs leading to study withdrawal, 
information on concomitant medications associated with those events, and any nonstudy vaccinations. In addition, study personnel will collect information 
on known participant exposure to someone with known COVID-19 or SARS-CoV-2 infection and on participant experience of COVID-19 symptoms. 
14. All concomitant medications and nonstudy vaccinations will be recorded throughout the study; and all concomitant medications relevant to or for the 
treatment of an SAE or MAAE will be recorded from Day 1 through the final visit (Day 209). 
 

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Table 18: 
Schedule of Assessments Part 3 (For Participants Who Receive a Single Dose)  
Visit Number 
0 
1 
2 
3 
4 
5 
6 
- 
7 
Type of Visit 
C 
C 
C 
Virtual 
Call 
C 
C 
C 
SFU 
C 
Month Timepoint 
 
M0 
 
 
M1 
M2 
M3 
SC 
M6 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D3 
D8 
D29 
D57 
D85 
Every 6weeks 
D99-1412 
D181 
Window Allowance (Days) 
- 7 
 
-2 
+ 3 
+ 7 
+3 
+7 
±3 
+ 7 
Days Since Most Recent Injection 
- 
0 
3 
7 
28 
56 
84 
- 
180 
Informed consent/assent form, demographics, concomitant medications, 
medical history  
X 
 
 
 
 
 
 
 
 
Review of inclusion and exclusion criteria3 
X 
X 
 
 
 
 
 
 
 
Physical examination including vital signs, height, weight4 
X 
X 
 
 
X 
 
 
 
X 
Pregnancy test5 
X 
X 
 
 
 
 
 
 
 
Study injection (including 30-minute post dose observation period) 
 
X 
 
 
 
 
 
 
 
Blood sample for potential biomarker analysis6 
 
 
X 
 
 
 
 
 
 
Blood sample for vaccine immunogenicity7 
 
X 
 
 
X 
 
X 
 
X 
Nasal swab sample for SARS-CoV-28 
 
X 
 
 
X 
 
X 
 
X 
Surveillance for COVID-19/ Illness visit9/ Unscheduled visit 
 
X 
X 
X 
X 
X 
X 
X 
X 
eDiary activation for recording solicited ARs (7 days)10 
 
X 
 
 
 
 
 
 
 
Review of eDiary data11 
 
 
 
X 
 
 
 
 
 
Follow-up safety telephone calls12 
 
 
 
 
 
 
 
X 
 
Recording of unsolicited AEs 
 
X 
X 
X 
X 
 
 
 
 
Recording of MAAEs and concomitant medications relevant to or for the 
treatment of the MAAE13 
 
X 
X 
X 
X 
X 
X 
X 
X 

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Visit Number 
0 
1 
2 
3 
4 
5 
6 
- 
7 
Type of Visit 
C 
C 
C 
Virtual 
Call 
C 
C 
C 
SFU 
C 
Month Timepoint 
 
M0 
 
 
M1 
M2 
M3 
SC 
M6 
Study Visit Day 
D01 
(Screening) 
D1 (Baseline) 
D3 
D8 
D29 
D57 
D85 
Every 6weeks 
D99-1412 
D181 
Window Allowance (Days) 
- 7 
 
-2 
+ 3 
+ 7 
+3 
+7 
±3 
+ 7 
Days Since Most Recent Injection 
- 
0 
3 
7 
28 
56 
84 
- 
180 
Recording of SAEs and concomitant medications relevant to or for the 
treatment of the SAE13 
 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of AESI 
 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of AEs leading to withdrawal 
 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of concomitant medications and nonstudy vaccinations13 
 
X 
X 
X 
X 
X 
X 
X 
X 
Study completion 
 
 
 
 
 
 
 
 
X 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; BMI = body mass index; C = clinic visit; 
COVID-19 = coronavirus disease 2019; D = day; eDiary = electronic diary; FDA = USA Food and Drug Administration; IP = investigational product; 
IRB = institutional review board; M = month; MAAE = medically attended AE; NP = nasopharyngeal; SC = safety (telephone) call; SFU = safety follow-up; 
RT-PCR = reverse transcriptase polymerase chain reaction; SAE = serious adverse event; SARS-CoV-2 = Severe Acute Respiratory Syndrome coronavirus 2. 
Note: In accordance with FDA Guidance on Conduct of Clinical Trials of Medical Products during COVID-19 Public Health Emergency (DHHS 2020), 
investigators may convert study site visits to home visits or telemedicine visits with the approval of the Sponsor. 
Note: All scheduled study visits should be completed within the respective visit windows. If the participant is not able to attend a study site visit due to the 
COVID-19 pandemic (self-quarantine or disruption of study site activities following business continuity plans and/or local government mandates for “stay at 
home” or “shelter in place”), a safety telephone call to the participant should be made in place of the study site visit. The safety telephone call should 
encompass all scheduled visit assessments that can be completed remotely, such as assessment for AEs and concomitant medications (eg, as defined in 
scheduled safety telephone calls). Home visits will be permitted for all nondosing visits, except for Screening, if a participant cannot visit the study site due to 
the COVID-19 pandemic. Home visits must be permitted by the study site IRB and the participant via informed consent/assent and have prior approval from 
the Sponsor (or its designee). 
1. 
Day 0 and Day 1 may be combined on the same day. Additionally, the Day 0 Visit may be performed over multiple visits if they occur within the 7-day 
Screening window. 
2 
Safety follow-up via a safety telephone call will be performed every 6 weeks from Day 99 to Day 141. 

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3. 
Review of inclusion and exclusion criteria will be conducted during Screening. However, this review will be conducted on Day 1 if Screening and Baseline 
procedures are conducted on the same day. 
4. 
Physical examination: A full physical examination, including height, weight, and vital signs will be performed at Screening, Day 1, Day 29, and Day 181. 
BMI will be calculated only at Screening Visit (Day 0). Symptom-directed physical examinations may be performed at other timepoints at the discretion of 
the investigator. On the injection day before injection and again 7 days after injection, the arm receiving the injection should be examined and the associated 
lymph nodes should be evaluated. Any clinically significant finding identified during a study visit should be reported as a MAAE. Vital signs are to be 
measured predose and postdose on day of injection (Day 1). When applicable, vital signs should be measured before blood collection. Participants who are 
febrile (body temperature ≥38.0°C/100.4°F) before injection on Day 1 must have the visit rescheduled within the relevant visit window to receive the 
injection. Afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 
5. 
Pregnancy test at Screening and Day 1 will be a point-of-care urine test. At the discretion of the investigator, a pregnancy test either via blood or point-of-
care urine test can be performed at any time. 
6. 
Serum and plasma samples from two ~4 mL blood draws. Biomarker plasma and biomarker serum samples will be stored for potential future biomarker 
assessment. 
7. 
Sample must be collected prior to dosing of injection on Day 1. 
8. 
The nasal swab sample will be used to ascertain the presence of SARS-CoV-2 via RT-PCR. 
9. 
An unscheduled visit may be prompted by reactogenicity issues, illness visit criteria for COVID-19, or new or ongoing AEs. If a participant meets the 
prespecified criteria of suspicion for COVID-19 (Section 7.1.6), the participants will be asked to return within 72 hours or as soon as possible to the study 
site for an unscheduled illness visit, to include a nasal swab sample (for RT-PCR testing) and other clinical evaluations. If a study site visit is not possible, a 
home visit may be arranged to collect the NP or nasal sample and conduct clinical evaluations. If a home visit is not possible, the participant will be asked to 
submit a saliva sample to the study site by a Sponsor-approved method. At this illness visit, the NP or nasal swab samples will be collected to evaluate for 
the presence of SARS-CoV-2 infection. NP or nasal swab samples will also be tested for the presence of other respiratory pathogens. In addition, the study 
site may collect an additional NP or nasal sample for SARS-CoV-2 testing to be able to render appropriate medical care for the study participant as 
determined by local standards of care. Additionally, clinical information will be carefully collected to evaluate the severity of the clinical case. 
10. Diary entries will be recorded by the participant at approximately 30 minutes after injection while at the study site with instruction provided by study staff. 
Study participants will continue to record entries in the eDiary each day after they leave the study site, preferably in the evening, on the day of injection and 
for 6 days following injection. If a solicited local or systemic AR continues beyond Day 7 after vaccination, the participant will be prompted to capture 
details of the solicited local or systemic AR in the eDiary until the AR resolves or the next IP injection occurs, whichever occurs first; capture of details of 
ARs in the eDiary should not exceed 28 days after vaccination. 
11. ARs recorded in eDiaries beyond Day 7 after vaccination should be reviewed either via telephone call or at the following study visit. 
12. Trained study site personnel will call all participants to collect information relating to any AEs, MAAEs, SAEs, AEs leading to study withdrawal, 
information on concomitant medications associated with those events, and any nonstudy vaccinations. In addition, study personnel will collect information 
on known participant exposure to someone with known COVID-19 or SARS-CoV-2 infection and on participant experience of COVID-19 symptoms. 
13. All concomitant medications and nonstudy vaccinations will be recorded throughout the study; and all concomitant medications relevant to or for the 
treatment of an SAE or MAAE will be recorded from Day 1 through the final visit (Day 181). 

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10.2. 
APPENDIX 2: Study Governance Considerations  
10.2.1. 
Regulatory and Ethical Considerations  
This study will be conducted in accordance with the protocol and with the following: 
• Consensus ethical principles derived from international guidelines including the 
Declaration of Helsinki and Council for International Organizations of Medical 
Sciences International Ethical Guidelines. 
• Applicable ICH GCP Guidelines. 
• Applicable laws and regulatory requirements. 
• The protocol, protocol amendments, ICF, IB, and other relevant documents (eg, 
advertisements) must be submitted to an IRB by the investigator and reviewed and 
approved by the IRB before the study is initiated. 
• Any amendments to the protocol will require IRB approval before implementation of 
changes made to the study design, except for changes necessary to eliminate an 
immediate hazard to study participants. 
• The investigator will be responsible for the following: 
− Providing written summaries of the status of the study to the IRB annually or 
more frequently in accordance with the requirements, policies, and procedures 
established by the IRB 
− Notifying the IRB of SAEs or other significant safety findings as required by IRB 
procedures 
− Providing oversight of the conduct of the study at the site and adherence to 
requirements of 21 CFR, ICH guidelines, the IRB, European regulation 536/2014 
for clinical studies (if applicable), and all other applicable local regulations. 
10.2.2. 
Study Monitoring  
Before an investigational site can enter a participant into the study, a representative of the 
Sponsor or its representatives will visit the investigational study site to do the following: 
• Determine the adequacy of the facilities 
• Discuss with the investigator(s) and other personnel their responsibilities with regard 
to protocol adherence, and the responsibilities of the Sponsor or its representatives. 
This will be documented in a clinical study agreement between the Sponsor, the 
designated CRO, and the investigator. 
According to ICH GCP guidelines, the Sponsor of the study is responsible for ensuring the 
proper conduct of the study with regard to protocol adherence and validity of data recorded on 
the eCRFs. The study monitor’s duties are to aid the investigator and the Sponsor in the 
maintenance of complete, accurate, legible, well-organized, and easily retrievable data. The 
study monitor will advise the investigator of the regulatory necessity for study-related 
monitoring, audits, IRB review, and inspection by providing direct access to the source 

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data/documents. In addition, the study monitor will explain to and interpret for the investigator 
all regulations applicable to the clinical evaluation of an IP as documented in ICH guidelines. 
It is the study monitor’s responsibility to inspect the eCRFs and source documentation 
throughout the study to protect the rights of the participants; to verify adherence to the protocol; 
to verify completeness, accuracy, and consistency of the data; and to confirm adherence of study 
conduct to any local regulations. Details will be outlined in the Clinical Monitoring Plan. During 
the study, a monitor from the Sponsor or a representative will have regular contacts with the 
investigational site, for the following: 
• Provide information and support to the investigator(s). 
• Confirm that facilities remain acceptable. 
• Confirm that the investigational team is adhering to the protocol, that the data are 
being accurately recorded in the eCRFs, and that IP accountability checks are being 
performed. 
• Perform source data verification. This includes a comparison of the data in the eCRFs 
with the participant’s medical records at the hospital or practice, and other records 
relevant to the study. This will require direct access to all original records for each 
participant (eg, clinical charts or electronic medical record system). 
• Record and report any protocol deviations not previously sent. 
• Confirm AEs and SAEs have been properly documented on eCRFs and confirm any 
SAEs have been forwarded to the SAE Hotline, and those SAEs that met criteria for 
reporting have been forwarded to the IRB. 
The monitor will be available between visits if the investigator(s) or other staff needs 
information or advice. 
10.2.3. 
Audits and Inspections  
The Sponsor, their designee(s), the IRB, or regulatory authorities will be allowed to conduct 
study site visits to the investigational facilities for the purpose of monitoring or inspecting any 
aspect of the study. The investigator agrees to allow the Sponsor, their designee(s), the IRB, or 
regulatory authorities to inspect the IP storage area, IP stocks, IP records, participant charts and 
study source documents, and other records relative to study conduct. 
Authorized representatives of the Sponsor, a regulatory authority, and any IRB may visit the 
study site to perform audits or inspections, including source data verification. The purpose of a 
Sponsor audit or inspection is to systematically and independently examine all study-related 
activities and documents to determine whether these activities were conducted, and data were 
recorded, analyzed, and accurately reported according to the protocol, ICH E6(R2) GCP, and any 
applicable regulatory requirements. The investigator should contact the Sponsor immediately if 
contacted by a regulatory agency about an inspection. 
The principal investigator must obtain IRB approval for the investigation. Initial IRB approval, 
and all materials approved by the IRB for this study including the participant consent/assent form 
and recruitment materials, must be maintained by the investigator and made available for 
inspection. 

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10.2.4. 
Financial Disclosure  
The investigator is required to provide financial disclosure information to allow the Sponsor to 
submit the complete and accurate certification or disclosure statements required under 21 CFR 54. 
In addition, the investigator must provide the Sponsor with a commitment to promptly update 
this information if any relevant changes occur during the course of the investigation and for 
1 year following the completion of the study. 
The Sponsor, the CRO, and the study site are not financially responsible for further testing or 
treatment of any medical condition that may be detected during the screening process. In addition, 
in the absence of specific arrangements, the Sponsor, the CRO, and the study site are not 
financially responsible for further treatment of the disease under study. 
10.2.5. 
Recruitment Procedures  
Advertisements to be used for the recruitment of study participants, and any other written 
information regarding this study to be provided to the participant should be submitted to the 
Sponsor for approval. All documents must be approved by the IRB. 
10.2.6. 
Informed Consent/Assent Process  
The informed consent/assent document(s) must meet the requirements of 21 CFR 50, local 
regulations, ICH guidelines, Health Insurance Portability and Accountability Act, where 
applicable, and the IRB or study site. All consent documents will be approved by the appropriate 
IRB. The actual ICF used at each study site may differ, depending on local regulations and IRB 
requirements. However, all versions of the ICF must contain the standard information found in 
the sample ICF provided by the Sponsor. Any change to the content of the ICF must be approved 
by the Sponsor and the IRB prior to the ICF being used. 
If new information becomes available that may be relevant to the participant’s willingness to 
continue participation in the study, this will be communicated to them in a timely manner. Such 
information will be provided via a revised ICF or an addendum to the original ICF. 
The investigator or his/her representative will explain the nature of the study to the participant 
and answer all questions regarding the study. 
The investigator is responsible for ensuring that the participant fully understands the nature and 
purpose of the study. Information should be given in both oral and written form whenever 
possible. 
No participant should be obliged to participate in the study. The participant must be informed 
that participation is voluntary. Participants, their relatives, guardians, or (if applicable) LARs 
must be given ample opportunity to inquire about details of the study. The information must 
make clear that refusal to participate in the study or withdrawal from the study at any stage is 
without any prejudice to the participant’s subsequent care. 
The participant must be allowed sufficient time to decide whether they wish to participate in the 
study. 
The participant must be made aware of, and give consent to, direct access to his/her source 
medical records by study monitors, auditors, the IRB, and regulatory authorities. The participant 
should be informed that such access will not violate participant confidentiality or any applicable 

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regulations. The participant and/or participants’ parent(s)/LAR(s) should also be informed that 
he/she is authorizing such access by signing the ICF. 
A copy of the ICF(s) must be provided to the participant and/or participants’ parent(s)/LAR(s). 
A participant who is rescreened is not required to sign another ICF if the rescreening occurs 
within 28 days from the previous ICF signature date (within the initial Screening Period). 
The ICF will also explain that excess serum from immunogenicity testing may be used for future 
research, which may be performed at the discretion of the Sponsor to further characterize the 
immune response to SARS-CoV-2, additional assay development, and the immune response 
across CoVs. 
10.2.7. 
Protocol Amendments  
No change or amendment to this protocol may be made by the investigator or the Sponsor after 
the protocol has been agreed to and signed by all parties unless such change(s) or amendment(s) 
has (have) been agreed upon by the investigator or the Sponsor. Any change agreed upon will be 
recorded in writing, and the written amendment will be signed by the investigator and the 
Sponsor. IRB approval is required prior to the implementation of an amendment, unless 
overriding safety reasons warrant immediate action, in which case the IRB(s) will be promptly 
notified. 
Any modifications to the protocol or the ICF, which may impact the conduct of the study, 
potential benefit of the study, or may affect participant safety, including changes of study 
objectives, study design, participant population, sample sizes, study procedures, or significant 
administrative aspects will require a formal amendment to the protocol. Such an amendment will 
be released by the Sponsor, agreed by the investigator(s), and approved by the relevant IRB(s) 
prior to implementation. A signed and dated statement that the protocol, any subsequent relevant 
amended documents, and the ICF have been approved by relevant IRB(s) must be provided to 
the Sponsor before the study is initiated. 
Administrative changes of the protocol are minor corrections and/or clarifications that have no 
effect on the way the study is to be conducted. These administrative changes will be released by 
the Sponsor, agreed by the investigators, and notified to the IRB(s). 
10.2.8. 
Protocol Deviations  
The noncompliance may be either on the part of the participant, the investigator, or the study site 
staff. As a result of protocol deviations, corrective actions are to be developed by the study site 
and implemented promptly. 
After a participant proceeds to the Participant Decision Visit (Part 1A) of the study, participants 
who received mRNA-1273 will continue to follow the open-label Part 1A SoA (Table 10). 
Participants who received placebo will transition to open-label Part 1B of the study and will 
follow the Part 1B SoA (Table 12). Participants who transitioned to Part 1C-1, at least 5 months 
after last dose, will follow the Part 1C-1 SoA (Table 13). Eligible participants that completed 
their primary COVID-19 vaccination series under EUA and choose to receive a BD will follow 
Part 1C-2 SoA (Table 14). Participants enrolled in Part 2 will follow Part 2 SoA (Table 15 and 
Table 16). Participants enrolled in Part 3 will follow Part 3 SoA (Table 17 and Table 18). 

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It is the responsibility of the study site investigator to use continuous vigilance to identify and 
report protocol deviations to the Sponsor or its designee. All protocol deviations must be 
addressed in study source documents, reported to study monitor. Protocol deviations must be 
sent to the reviewing IRB per their policies. The study site investigator is responsible for 
knowing and adhering to the reviewing IRB requirements. 
10.2.9. 
Data Protection  
Participants will be assigned a unique identifier by the Sponsor. Any participant records or 
datasets that are transferred to the Sponsor will contain the identifier only; participant names or 
any information which would make the participant identifiable will not be transferred. 
The participant must be informed that his/her personal study-related data will be used by the 
Sponsor in accordance with local data protection law. The level of disclosure must also be 
explained to the participant. 
The participant must be informed that his/her medical records may be examined by clinical QA 
auditors or other authorized personnel appointed by the Sponsor, by appropriate IRB members, 
and by inspectors from regulatory authorities. 
Individual participant medical information obtained as a result of this study is considered 
confidential, and disclosure to third parties is prohibited. Information will be accessible to 
authorized parties or personnel only. Medical information may be given to the participant’s 
physician or to other appropriate medical personnel responsible for the participant’s well-being. 
Each participant will be asked to complete a form allowing the investigator to notify the 
participant’s primary health care provider of his/her participation in this study. 
All laboratory specimens, evaluation forms, reports, and other records will be identified in a 
manner designed to maintain participant confidentiality. All records will be kept in a secure 
storage area with limited access. Clinical information will not be released without the written 
permission of the participant, except as necessary for monitoring and auditing by the Sponsor, 
its designee, relevant regulatory authority, or the IRB. 
The investigator and all employees and coworkers involved with this study may not disclose or 
use for any purpose other than performance of the study, any data, record, or other unpublished, 
confidential information disclosed to those individuals for the purpose of the study. Prior written 
agreement from the Sponsor or its designee must be obtained for the disclosure of any 
confidential information to other parties. 
10.2.10. 
Sample Retention and Future Biomedical Research  
The retention period of laboratory samples will be 20 years, or as permitted by local regulations, 
to address further scientific questions related to mRNA-1273 or antirespiratory virus immune 
response. In addition, identifiable samples can be destroyed at any time at the request of the 
participant. During the study, or during the retention period, in addition to the analysis outlined 
in the study endpoints, exploratory analysis may be conducted using other Ab-based 
methodologies on any remaining blood or serum samples, including samples from participants 
who are screened but are not subsequently enrolled. These analyses will extend the search for 
other potentially relevant biomarkers to investigate the effect of mRNA-1273, as well as to 
determine how changes in biomarkers may relate to exposure and clinical outcomes. A decision 

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to perform such exploratory research may arise from new scientific findings related to the drug 
class or disease, as well as reagent and assay availability. 
10.2.11. 
Dissemination of Clinical Study Data  
The Sponsor shares information about clinical trials and results on publicly accessible websites, 
based on international and local legal and regulatory requirements, and other clinical trial 
disclosure commitments established by pharmaceutical industry associations. These websites 
include clinicaltrials.gov, EU clinical trial register (eu.ctr), as well as some national registries. 
In addition, results from clinical trials are required to be submitted to peer-reviewed journals 
following internal company review for accuracy, fair balance, and intellectual property. For 
those journals that request sharing of the analyzable data sets that are reported in the publication, 
interested researchers are directed to submit their request to clinicalstudydatarequest.com. 
Individual participant data and supporting clinical documents are available for request at 
clinicalstudydatarequest.com. While making information available, the privacy of participants in 
clinical studies sponsored by the Sponsor is assured. Details on data sharing criteria and process 
for requesting access can be found at this web address: clinicalstudydatarequest.com. 
10.2.12. 
Data Quality Assurance and Quality Control  
Data collection is the responsibility of the clinical study staff at the study site under the 
supervision of the study site investigator. The investigator is responsible for ensuring the 
accuracy, completeness, legibility, and timeliness of the data reported. 
• All participant data relating to the study will be recorded in the eCRF unless 
transmitted to the Sponsor or designee electronically (eg, laboratory data). The 
investigator is responsible for verifying that data entries are accurate and correct 
by physically or electronically signing the eCRF. 
• The investigator must maintain accurate documentation (source data) that 
supports the information entered in the eCRF. 
• The investigator must permit study-related monitoring, audits, IRB review, and 
regulatory agency inspections and provide direct access to source data documents. 
• Monitoring details describing strategy (eg, risk-based initiatives in operations and 
quality such as Risk Management and Mitigation Strategies and Analytical 
Risk-Based Monitoring), methods, responsibilities and requirements, including 
handling of noncompliance issues and monitoring techniques (central, remote, or 
on-site monitoring) are provided in the Clinical Monitoring Plan. 
• The Sponsor or designee is responsible for the data management of this study 
including quality checking of the data. 
• The Sponsor assumes accountability for actions delegated to other individuals (eg, 
CRO). 
• Study monitors will perform ongoing source data verification to confirm that data 
entered into the eCRF by authorized study site personnel are accurate, complete, 
and verifiable from source documents; that the safety and rights of participants are 

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being protected; and that the study is being conducted in accordance with the 
currently approved protocol and any other study agreements, ICH GCP, and all 
applicable regulatory requirements. 
• Records and documents, including signed ICFs, pertaining to the conduct of this 
study must be retained by the investigator for a period of at least 2 years after the 
last marketing application approval or, if not approved, 2 years following the 
discontinuance of the test article for investigation. If this requirement differs from 
any local regulations, the local regulations will take precedence unless the local 
retention policy is less than 2 years. No records may be destroyed during the 
retention period without the written approval of the Sponsor. No records may be 
transferred to another location or party without written notification to the Sponsor. 
Quality assurance includes all the planned and systematic actions that are established to ensure 
that the clinical study is performed and the data are generated, documented (recorded), and 
reported according to ICH GCP and local/regional regulatory standards. 
A QA representative from the Sponsor or a qualified designee, who is independent of and 
separated from routine monitoring, may periodically arrange inspections/audits of the clinical 
study by reviewing the data obtained and procedural aspects. These inspections may include 
on-site inspections/audits and source data checks. Direct access to source documents is required 
for the purpose of these periodic inspections/audits. 
10.2.13. 
Data Collection and Management  
This study will be conducted in compliance with ICH CGP guidelines. This study will also be 
conducted in accordance with the most recent version of the Declaration of Helsinki. 
This study will use electronic data collection to collect data directly from the study site using 
eCRFs. The investigator is responsible for ensuring that all sections of each eCRF are completed 
promptly and correctly and that entries can be verified against any source data. 
Study monitors will perform source document verification to identify inconsistencies between 
the eCRFs and source documents. Discrepancies will be resolved in accordance with the 
principles of GCP. Detailed study monitoring procedures are provided in the Clinical Monitoring 
Plan. 
Adverse events will be coded with MedDRA. Concomitant medications will be coded using 
WHO - Drug Dictionary. 
10.2.14. 
Source Documents  
Source documents are original documents or certified copies, and include, but are not limited to, 
eDiaries, medical and hospital records, screening logs, informed consent/assent forms, telephone 
contact logs, and worksheets. Source documents provide evidence for the existence of the 
participant and substantiate the integrity of the data collected. Source documents are filed at the 
investigator’s study site. 
Data reported on the CRF or entered in the eCRF that are transcribed from source documents 
must be consistent with the source documents or the discrepancies must be explained. The 

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investigator may need to request previous medical records or transfer records, depending on the 
study. Also, current medical records must be available. 
The Sponsor or its designee requires that the investigator prepare and maintain adequate and 
accurate records for each participant treated with the IP. Source documents such as any hospital, 
clinic, or office charts, and the signed ICFs are to be included in the investigator’s files with the 
participant’s study records. 
10.2.15. 
Retention of Records  
The principal investigator must maintain all documentation relating to the study for a period of at 
least 2 years after the last marketing application approval or, if not approved, 2 years following 
the discontinuance of the test article for investigation. If this requirement differs from any local 
regulations, the local regulations will take precedence unless the local retention policy is 
> 2 years. 
If it becomes necessary for the Sponsor or the regulatory authority to review any documentation 
relating to the study, the investigator must permit access to such records. No records will be 
destroyed without the written consent of the Sponsor, if applicable. It is the responsibility of the 
Sponsor to inform the investigator when these documents no longer need to be retained. 
10.2.16. 
Study and Site Closure  
If the study is prematurely terminated or suspended, the Sponsor shall promptly inform the 
investigators, the IRBs, the regulatory authorities, and any CRO(s) used in the study of the 
reason for termination or suspension, as specified by the applicable regulatory requirements. The 
investigator shall promptly inform the participants and should assure appropriate participant 
therapy and/or follow-up. 
The Sponsor or designee reserves the right to close the study site or terminate the study at any 
time for any reason at the sole discretion of the Sponsor. 
The investigator may initiate study site closure at any time, provided there is reasonable cause 
and sufficient notice is given in advance of the intended termination. 
Reasons for the early closure of a study site by the Sponsor or investigator may include but are 
not limited to: 
• Continuation of the study represents a significant medical risk to participants 
• Failure of the investigator to comply with the protocol, the requirements of the 
IRB or local health authorities, the Sponsor’s procedures, or GCP guidelines 
• Inadequate recruitment of participants by the investigator 
• Discontinuation of further mRNA-1273 development 
Study sites will be closed upon study completion. A study site is considered closed when all 
required documents and study supplies have been collected and a study site closure visit has been 
performed. 

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10.2.17. 
Publication Policy  
The results of this study may be published or presented at scientific meetings. If this is foreseen, 
the investigator agrees to submit all manuscripts or abstracts to the Sponsor before submission. 
This allows the Sponsor to protect proprietary information and to provide comments. 
The Sponsor will comply with the requirements for publication of study results. In accordance 
with standard editorial and ethical practice, the Sponsor will generally support publication of 
multicenter studies only in their entirety and not as individual study site data. In this case, a 
coordinating investigator will be designated by mutual agreement. 
Authorship will be determined by mutual agreement and in line with International Committee of 
Medical Journal Editors authorship requirements. 
The clinical study plan and the results of the study will be published on www.ClinicalTrials.gov 
in accordance with 21 CFR 50.25(c). The results of and data from this study belong to the 
Sponsor. 
10.2.18. 
BMI Charts for Boys and Girls  
For boys aged 5 through 19 years: 
 

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For girls aged 5 through 19 years: 
 

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10.3. 
APPENDIX 3: Contraceptive Guidance  
Woman of Childbearing Potential (WOCBP) 
Females of childbearing potential are those who are considered fertile following menarche and 
until becoming postmenopausal unless permanently sterile (see below). If fertility is unclear (eg, 
amenorrhea in adolescents or athletes) and a menstrual cycle cannot be confirmed before first 
dose of study treatment, additional evaluation should be considered. 
Women in the following categories are not considered WOCBP: 
1. Premenarchal 
2. Premenopausal, surgically sterile female with 1 of the following: 
• Documented complete hysterectomy 
• Documented surgical sterilization 
For individuals with permanent infertility due to an alternate medical cause other than the above, 
(eg, Mullerian agenesis, androgen insensitivity), investigator discretion should be applied in 
determining study entry. 
Note: Documentation can come from the study site personnel’s review of the participant’s 
medical records, medical examination, or medical history interview. 
Contraception Guidance: 
A highly effective method of birth control is defined as one which results in a low failure rate 
(eg, less than 1% per year) when used consistently and correctly, such as implants, injectables, 
combined oral contraceptives, some intrauterine devices, sexual abstinence or vasectomized 
partner. For participants using a hormonal contraceptive method, information regarding the 
product under evaluation and its potential effect on the contraceptive should be addressed. 
Adequate female contraception is defined as consistent and correct use of an FDA-approved 
contraceptive method in accordance with the product label. For example: 
• Barrier method (such as condoms, diaphragm, or cervical cap) used in conjunction 
with spermicide 
• Intrauterine device 
• Prescription hormonal contraceptive taken or administered via oral (pill), transdermal 
(patch), subdermal, or IM route 
• Sterilization of a female participant’s monogamous male partner prior to entry into 
the study 
Note that periodic abstinence (eg, calendar, ovulation, symptothermal, postovulation methods) 
and withdrawal are not acceptable methods of contraception. 

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10.4. 
APPENDIX 4: Adverse Event of Special Interest Terms  
Investigators should report all events which fall into the following categories as an AESI per the 
reporting processes specified in Section 7.5.5. The following AESIs are medical concepts that 
may be related to COVID-19 or are of interest in COVID-19 vaccine safety surveillance. Even if 
the events below occur in the setting of a COVID infection, the event should still be reported as 
an AESI if it is one of the medical concepts described in Table 19. 
Table 19: 
Medical Concepts that Qualify as Adverse Events of Special Interest  
Anosmia, Ageusia 
• 
New onset COVID associated or idiopathic events without other 
etiology excluding congenital etiologies or trauma 
Subacute thyroiditis 
• 
Including but not limited to events of atrophic thyroiditis, 
autoimmune thyroiditis, immune-mediated thyroiditis, silent 
thyroiditis, thyrotoxicosis and thyroiditis 
Acute pancreatitis 
• 
Including but not limited to events of autoimmune pancreatitis, 
immune-mediated pancreatitis, ischemic pancreatitis, edematous 
pancreatitis, pancreatitis, acute pancreatitis, hemorrhagic pancreatitis, 
necrotizing pancreatitis, viral pancreatitis, and subacute pancreatitis 
• 
Excluding known etiologic causes of pancreatitis (alcohol, gallstones, 
trauma, recent invasive procedures) 
Appendicitis  
• 
Include any event of appendicitis  
Rhabdomyolysis 
• 
New onset rhabdomyolysis without known etiology such as excessive 
exercise or trauma 
Acute respiratory distress 
syndrome 
• 
Including but not limited to new events of ARDS and respiratory 
failure  
Coagulation disorders 
• 
Including but not limited to thromboembolic and bleeding disorders, 
disseminated intravascular coagulation, pulmonary embolism, deep 
vein thrombosis  
Acute cardiovascular injury 
• 
Including but not limited to myocarditis, pericarditis, 
microangiopathy, coronary artery disease, arrhythmia, stress 
cardiomyopathy, heart failure, or acute myocardial infarction 
Acute kidney injury 
• 
Include events with idiopathic or autoimmune etiologies 
• 
Exclude events with clear alternate etiology (trauma, infection, tumor, 
or iatrogenic causes such as medications or radiocontrast etc.) 
• 
Include all cases that meet the following criteria 
− 
Increase in serum creatinine by ≥0.3 mg/dl (≥26.5 µmol/l) within 
48 hours; 
OR 
− 
Increase in serum creatinine to ≥1.5 times baseline, known or 
presumed to have occurred within prior 7 days 
OR 
− 
Urine volume ≤0.5 ml/kg/hour for 6 hours 

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Acute liver injury 
• 
Include events with idiopathic or autoimmune etiologies 
• 
Exclude events with clear alternate etiology (trauma, infection, tumor, 
etc.) 
• 
Include all cases that meet the following criteria 
− 
3-fold elevation above the upper normal limit for ALT or AST 
OR 
− 
>2-fold elevation above the upper normal limit for total serum 
bilirubin or GGT or ALP 
Dermatologic findings  
• 
Chilblain-like lesions 
• 
Single organ cutaneous vasculitis 
• 
Erythema multiforme 
• 
Bullous rashes 
• 
Severe cutaneous ARs including but not limited to: SJS, TEN, 
DRESS, and fixed drug eruptions 
Multisystem inflammatory 
disorders  
• 
MIS-A 
• 
MIS-C 
• 
Kawasaki’s disease 
Thrombocytopenia 
• 
Platelet counts <150 x109 
• 
Including but not limited to immune thrombocytopenia, platelet 
production decreased, thrombocytopenia, thrombocytopenic purpura, 
thrombotic thrombocytopenic purpura, or HELLP syndrome 
Acute aseptic arthritis 
 
• 
New onset aseptic arthritis without clear alternate etiology (eg, gout, 
osteoarthritis, and trauma) 
New onset of or worsening of 
neurologic disease 
• 
Including but not limited to: 
− 
Guillain-Barre Syndrome 
− 
ADEM 
− 
Peripheral facial nerve palsy (Bell’s palsy) 
− 
Transverse myelitis 
− 
Encephalitis/encephalomyelitis 
− 
Aseptic meningitis 
− 
Febrile seizures 
− 
Generalized seizures/convulsions 
− 
Stroke (Hemorrhagic and nonhemorrhagic) 
− 
Narcolepsy 
Anaphylaxis  
• 
Anaphylaxis as defined PP. 
• 
Follow reporting procedures in protocol Section 7.5.5 
Other syndromes 
 
• 
Fibromyalgia 
• 
Postural orthostatic tachycardia syndrome 
• 
Chronic fatigue syndrome (includes myalgic encephalomyelitis and 
post viral fatigue syndrome) 
• 
Myasthenia gravis 

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Abbreviations: ADEM = acute disseminated encephalomyelitis; ALP = alkaline phosphatase; ALT = alanine 
transaminase; AST = aspartate aminotransferase; AR = adverse reaction; ARDS = acute respiratory distress 
syndrome; COVID = coronavirus disease; DRESS = drug reaction with eosinophilia and systemic symptoms; 
GGT = gamma-glutamyl transpeptidase; HELLP = hemolysis, elevated liver enzymes, and low platelets; 
MIS-A = multisystem inflammatory syndrome in adults; MIS-C = multisystem inflammatory syndrome in 
children; SJS = Stevens-Johnson syndrome; TEN = toxic epidermal necrolysis. 

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10.5. 
APPENDIX 5: Protocol Amendment History  
Amendment 6, 22 Jun 2023 
This amendment is considered to be substantial based on the criteria set forth in Article 10(a) of 
Directive 2001/20/EC of the European Parliament and the Council of the European Union. 
Main Rationale for the Amendment: 
The main purpose of this amendment is to update the primary immunogenicity objective of 
Part 3, per regulatory feedback, to evaluate the effectiveness of a single 50 μg dose of 
mRNA-1273.222 in COVID-19 vaccine-naïve, baseline SARS-CoV-2 positive individuals 12 to 
17 years of age, by comparing the immune response in these individuals at 1-month post single 
dose (50 μg mRNA-1273.222) to the 1-month post Dose 2 (100 μg mRNA-1273) immune 
response from baseline SARS-CoV-2 negative participants in Study P301 adults for whom 
clinical vaccine efficacy was demonstrated. 
Summary of Major Changes in Protocol Amendment 6: 
The Summary of Changes table provided below describes the major changes made in Protocol 
Amendment 6 relative to Protocol Amendment 5, including the sections modified and the 
corresponding rationales. The synopsis of Protocol Amendment 6 has been modified to 
correspond to changes in the body of the protocol. Formatting edits were introduced throughout 
the protocol to accommodate the recent update to the Sponsor’s style guide. Literature references 
were updated based on changes in cited content. Minor copy edits and administrative updates 
were made throughout the protocol to align with new content as well as for clarity, readability, 
and/or accuracy. 
Section Number and 
Name 
Description of Change 
Brief Rationale 
Section 2 Objectives and 
Endpoints; Section 3 Study 
Design; Section 3.2 
Scientific Rationale for 
Study Design; Section 
8.2.3 Statistical Hypothesis 
(Part 3); Section 8.3.3 
Power and Sample Size 
(Part 3); Section 8.5.8 Part 
3 Analysis; Section 8.6 
Multiplicity Adjustment 
Modifications to primary and (key) 
secondary immunogenicity objectives and 
endpoints, statistical hypothesis, power and 
sample size, and analysis in Part 3 of the 
study. 
Revised primary immunogenicity objective 
to include coprimary immunogenicity 
endpoints: 
• 
To demonstrate superior GM value of 
Ab against Omicron BA.4/BA.5 after 
single 50 μg dose of mRNA-1273.222 in 
COVID-19 vaccine-naïve, baseline 
SARS-CoV-2 positive adolescents in 
Part 3 of study P203 compared to GM 
value of Ab against Omicron 
BA.4/BA.5 after 2 doses (100 μg each) 
of mRNA-1273 in baseline SARS-CoV-
2 negative young adult participants 18 to 
25 years of age in Study P301 
Updates to 
immunogenicity 
objectives and endpoints 
were made in response to 
regulatory feedback. 

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Section Number and 
Name 
Description of Change 
Brief Rationale 
• 
To demonstrate noninferior GM value of 
Ab against ancestral strain after single 
50 μg dose of mRNA-1273.222 in 
COVID-19 vaccine-naïve, baseline 
SARS-CoV-2 positive adolescents in 
Part 3 of study P203 compared to GM 
value of Ab against ancestral strain after 
2 doses (100 μg each) of mRNA-1273 in 
baseline SARS-CoV-2 negative young 
adult participants 18 to 25 years of age 
in Study P301 
Key secondary endpoints were revised to 
secondary endpoints without hypothesis 
testing. 
Section 3.1.3 Part 3 Study 
Design; Section 8.3.3 
Power and Sample Size 
(Part 3) 
The target number of enrolled participants 
was also revised (from N of 500 to N of at 
least 300) according to the new sample size 
and power calculation (based on new 
information): With at least 300 adolescents 
enrolled, the study will have at least a 95% 
probability to observe at least 1 participant 
with an AE at a true AE rate of 1%. A 
sample size of approximately 168 
participants is required to sufficiently power 
the hypothesis testing of new 
coprimary immunogenicity endpoints, 
resulting in approximately 240 enrolled 
participants required for immunogenicity 
primary analysis after considering the 
potential 30% exclusion rate for the PP 
Immunogenicity Subset-baseline 
SARS-CoV-2 positive (PPIS-POS), as 
participants may be baseline SARS-CoV-2 
negative or have missing immunogenicity 
results due to any reason or protocol 
deviations impacting critical data. 
Update to sample size 
based revised Part 2 data 
based and made in 
response to regulatory 
feedback. 
Section 4.1.2 Exclusion 
Criteria 
Updated Exclusion Criterion #12 as follows: 
Any licensed vaccine within 28 days before 
the first dose of IP or plans for receipt of any 
licensed vaccine within 28 days before 
and/or after each dose of IP. 
Participants can be 
enrolled if they have 
received or plan to 
receive a licensed 
vaccine outside of these 
clarified windows and in 
between doses. 
Section 1.2.2 Clinical 
Studies 
Added Study mRNA-1273-P206 in the list 
of ongoing trials being conducted to support 
SARS-CoV-2 variants. 
Updated section with the 
latest information. 

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Section Number and 
Name 
Description of Change 
Brief Rationale 
Section 1.2.2.3 Phase 2/3 
Study mRNA-1273-P205; 
Section 3.2 Scientific 
Rationale for Study 
Design; Section 3.3 
Justification for Dose, 
Control Product, and 
Choice of Study Population 
Addition of interim results from Part 1C-1 
and Part 2. 
Updated section with the 
latest information. 
Section 1.2.2 Clinical 
Studies, Section 3.3 
Justification for Dose, 
Control Product, and 
Choice of Study Population 
Added latest effectiveness data on 
mRNA-1273.222 vaccine from literature 
based on the mRNA-1273-P205 Study. 
Updated section with the 
latest information. 
Table 7 Analysis Sets 
For the PP Immunogenicity Subset for Part 
3, clarified the following points: 
The PP Immunogenicity Subset for Part 3 
with baseline-positive SARS-CoV-2 status 
will serve as the population for the primary 
and secondary analysis of immunogenicity 
data at Day 29 in Part 3. The PP 
Immunogenicity Subset (Part 3, at Day 209) 
will serve as the population for the primary 
and secondary analysis of immunogenicity 
data at Day 209 in Part 3. 
Additionally, added the following note 
under Table 7: 
Positive SARS-CoV-2 status at baseline is 
defined as a positive RT-PCR test for 
SARS-CoV-2, and/or a positive serology 
test based on bAb specific to SARS-CoV-2 
nucleocapsid (as measured by Roche 
Elecsys Anti SARS-CoV-2 assay) on or 
before Day 1. Negative status is defined as a 
negative RT-PCR test for SARS-CoV-2, and 
a negative serology test based on bAb 
specific to SARS-CoV-2 nucleocapsid (as 
measured by Roche Elecsys Anti 
SARS-CoV-2 assay) on or before Day 1. 
Clarifying the definition 
of the SARS-CoV-2 
status at baseline. 
Abbreviations: AR = adverse reaction; bAb = binding antibody; CBER = Center for Biologics Evaluation and 
Research; D = day; EUA = Emergency Use Authorization; ICH = International Council for Harmonisation; 
IP = investigational product; MAAE = medically attended adverse event; mITT = modified intent-to-treat; 
nAb = neutralizing antibody; PP = per-protocol; SAE = serious adverse event; RT-PCR = reverse transcriptase 
polymerase chain reaction; SARS-CoV2 = Severe Acute Respiratory Syndrome coronavirus 2; SoA = Schedule of 
Assessments. 

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Amendment 5, 11 Oct 2022 
This amendment is considered to be substantial based on the criteria set forth in Article 10(a) of 
Directive 2001/20/EC of the European Parliament and the Council of the European Union. 
Main Rationale for the Amendment: 
To add an open-label Part 3 of the study with 50 µg of a bivalent mRNA-1273.222 vaccine given 
as 2 primary doses, 6 months apart, in COVID-19 vaccine-naïve participants. This amendment is 
expected to generate safety and immunogenicity data on 50 µg mRNA-1273.222 in the 12 to 
<18 years old adolescent population. 
Summary of Major Changes in Protocol Amendment 5: 
The Summary of Changes table provided below describes the major changes made in Protocol 
Amendment 5 relative to Protocol Amendment 4, including the sections modified and the 
corresponding rationales. The synopsis of Protocol Amendment 5 has been modified to 
correspond to changes in the body of the protocol. Formatting edits were introduced throughout 
the protocol to accommodate the recent update to the Sponsor’s style guide. Literature references 
were updated based on changes in cited content. Minor copy edits and administrative updates 
were made throughout the protocol to align with new content as well as for clarity, readability, 
and/or accuracy. 
Section Number and Name 
Description of Change 
Brief Rationale 
Section 1.1 Study Rationale 
Updated background text with 
recent epidemiology information, 
potential complications due to 
myocarditis, pericarditis, MIS-C, 
and Long COVID in the pediatric 
population, information on variants 
of concern, updates on ongoing 
studies, updates of findings from 
Study P301, Granting of EUA by 
FDA for adolescent population, and 
objectives of Part 3 of study with 
mRNA-1273.222. Additional 
information is described on the 
development of monovalent and 
bivalent vaccine candidates mRNA-
1273.214 and mRNA-1273.222.  
Updated to reflect COVID-19 
epidemiology and pathology 
information in the younger age 
groups, updated clinical studies, 
changes in COVID-19 vaccine 
regulations, and the rationale for the 
new Part 3 of the study. 
Section 1.2 Background and 
Overview 
Added information on the 
emergence of new Omicron 
variants, the authorization of 
mRNA-1273 under emergency use 
in adolescents, 12 to <18 years of 
age and on molecular 
characteristics and approval status 
of bivalent mRNA-1273.222. 
Updated to reflect the Sponsor’s 
activities around modification of 
mRNA-1273 vaccine against 
emerging Omicron variants. 
Section 1.2.1 Nonclinical Studies 
Added information on nonclinical 
studies in monovalent and bivalent 
vaccines. 
Evidence of protection of 
mRNA-1273 vaccines against 
different SARS-CoV-2 variants. 

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Section Number and Name 
Description of Change 
Brief Rationale 
Section 1.2.2 Clinical Studies 
Updated with additional studies in 
the adult and pediatric population 
on safety and immunogenicity of 
mRNA-1273 against new variants. 
Updates with interim results of 
current study and from Study 
mRNA-1273-P205 on the 
effectiveness of bivalent booster 
vaccine mRNA-1273.214 as well as 
safety findings 
Report of emerging case of 
myocarditis and/or pericarditis in 
the study. 
Updated to reflect emerging 
effectiveness and safety data from 
clinical studies in adult and 
pediatric populations. 
Section 2 Objectives and 
Endpoints; Section 3 Study Design; 
Section 8 Statistical Analysis Plan; 
Section 10.1 Appendix 1: Schedule 
of Assessments 
Modifications to primary objectives 
and endpoints, secondary 
endpoints, statistical hypothesis, 
power and sample size, analysis, 
and procedures in Part 2 of the 
study. 
Clarified that immunogenicity 
hypothesis testing will not be 
performed for Part 2. 
Discontinuation of enrollment in 
Part 1C-2 and Part 2 of the study. 
Clarified that Convalescent Visits 
are applicable to Part 1A and 1B 
only. 
Updated to reflect adjustments 
made due to small sample size for 
Part 2 of the study and the 
implications of adding Part 3 on the 
conduct of Part 2 of the study. 
Removed Convalescent visit 
because data/samples collected 
from this visit are not analyzed and 
to minimize the additional visits 
which could be burdensome for 
some participants. 
Section 1.1 Study Rationale, 
Section 1.2 Background and 
Overview, Section 1.3.1 Potential 
Benefits from Participation, Section 
1.3.2 Risks to Study Participants 
and Risk Mitigation; Section 2 
Objectives and Endpoints, Section 
3.1.3 Part 3 Study Design, Section 
3.2 Scientific Rationale for Study 
Design; Section 3.4 End-of-Study 
Definition; Section 4.1 Eligibility 
Criteria (Part 1A, Part 2, and Part 
3), Section 5.4 Study Treatment 
Compliance, Section 5.5.4; 
Concomitant Medications and 
Vaccines that May Lead to the 
Elimination of a Participant from 
Per-Protocol Analyses; Section 7 
Study Assessments and Procedures, 
Section 8 Statistical Analysis Plan, 
Section 8.4 Analysis Sets; Section 
8.5.7 Part 2 Analysis; Section 8.5.8 
Part 3 Analysis; Section 10.1 
Appendix 1: Schedule of 
Updated potential benefits to 
include effectiveness of mRNA-
1273.222 against disease caused by 
variants of concern. 
Updated risks to study participants 
with evaluation of risks related to 
myocarditis and pericarditis. 
Removed BD from Part 2 and 
convalescent visits from Part 1C-1, 
Part 1C-2, and Part 2 of the study. 
Added Part 3 where participants 
will get a 50 µg mRNA-1273.222 
administered in 2 doses 6 months 
apart. 
Generalized language around End-
of-Study definition. 
Updated exclusion criteria to 
include history of SARS-CoV-2 
infection or exposure to someone 
with COVID-19 within 90 days 
prior to receipt of the IP for 
participants in Part 3. Clarified 
Exclusion criteria in Part 1C2 that 
Updates to risks and benefits of the 
mRNA-1273 program based on 
development of bivalent vaccine 
and reports of myocarditis and 
pericarditis. 
Addition of a new part to study to 
test the safety and effectiveness of a 
bivalent mRNA against ancestral 
strain and Omicron in the young 
adolescent population. 

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Section Number and Name 
Description of Change 
Brief Rationale 
Assessments, Section 10.2.8 
Protocol Deviations 
monovalent COVID-19 primary 
series vaccines as well as 
authorized/approved bivalent 
vaccine against SARS-CoV-2 as 
4th booster are not exclusionary. 
Added a note to clarify that 
participants in Part 1C2 and Part 2 
planning to receive updated 
bivalent vaccine outside of study 
may continue in the study. 
On Section “exceptions to 
concomitant medications and 
vaccines that may lead to the 
elimination of a participant from 
per-protocol analyses” it was 
clarified that exclusion/withdrawal 
of participants who received 
COVID-19 vaccine apply only to 
participants in Part 1A. 
Updated study assessments and 
procedures to reflect updates to 
SoA for Part 1C-1, Part 1C-2, 
Part 2, and Part 3 of the study. 
Added PP Immunogenicity Subset 
for Part 3 in the Analysis Sets 
summary table. 
Clarified that confirmed 
symptomatic COVID-19 cases will 
be recorded as MAAEs.  
Section 7.5.5.1 Acute Myocarditis 
and/or Pericarditis 
Clarifications on the diagnostic 
evaluation, management, and 
reporting of myocarditis and/or 
pericarditis for the investigator. 
To enhance investigator 
understanding of practice related to 
mRNA-1273 and mRNA-1273.222-
associated AESI.  
Section 10.3 Appendix 3: 
Contraceptive Guidance 
Updated definition of highly 
effective birth control methods 
using definition containing ICH 
language. 
To ensure appropriate birth control 
method, accepted by health 
authorities outside the USA, is used 
in the study. 
Abbreviations: AESI = adverse event of special interest; AR = adverse reaction; bAb = binding antibody; 
CBER = Center for Biologics Evaluation and Research; D = day; EUA = Emergency Use Authorization; 
ICH = International Council for Harmonisation; IP = investigational product; MAAE = medically attended adverse 
event; mITT = modified intent-to-treat; nAb = neutralizing antibody; SAE = serious adverse event; 
RT-PCR = reverse transcriptase polymerase chain reaction; SARS-CoV2 = Severe Acute Respiratory Syndrome 
coronavirus 2; SoA = Schedule of Assessments. 
Amendment 4, 25 Jan 2022 
Main Rationale for the Amendment: 
To add 2 additional arms in the study, the 50 µg primary series and BD and heterologous 
boosting using the 50-µg dose. This amendment is expected to generate immunogenicity data on 
a lower primary series dose of 50 µg and heterologous boosting in the adolescent population. 

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Summary of Major Changes in Protocol Amendment 4: 
The Summary of Changes table provided below describes the major changes made in Protocol 
Amendment 4 relative to Protocol Amendment 3, including the sections modified and the 
corresponding rationales. The synopsis of Protocol Amendment 4 has been modified to 
correspond to changes in the body of the protocol. Minor copy edits and administrative updates 
were made throughout the protocol to align with new content as well as for clarity, readability, 
and/or accuracy. 
Section Number and Name 
Description of Change 
Brief Rationale 
Section 1.1. (Study Rationale), 
Section 1.3.2. (Risks to Study 
Participants and Risk Mitigation), 
Section 3.2. (Scientific Rationale for 
Study Design), Section 3.3. 
(Justification for Dose, Control 
Product, and Choice of Study 
Population) 
Added information about 50 µg 
dose levels and heterologous or 
mixed series coronavirus disease 
2019 (COVID-19) vaccines in 
adults 
Updated to reflect the change in data 
Section 1.2.2. (Clinical Studies) 
Added information about Study 
mRNA-1273-P205 which is 
evaluating boosters for variants  
Updated to reflect updated clinical 
studies 
Section 1.3.3. (Overall Benefit/Risk 
Conclusion), Section 2. (Objectives 
and Endpoints), Section 3.1. (General 
Design), Section 3.1.1.4. (Part 1C-2, 
Heterologous Booster Phase), 
Section 3.2. (Scientific Rationale for 
Study Design), Section 3.4. (End-of-
Study Definition) Section 4.4 (Study 
Eligibility Criteria [Part 1C-2 – 
Heterologous Booster Dose]), 
Section 5.4. (Study Treatment 
Compliance), Section 8.3.1.2.2. (Part 
1C-2 – Heterologous Booster Phase), 
Section 8.5.6.2. (Part 1C-2 – 
Heterologous Booster Phase 
Analysis), Section 10.1. 
(APPENDIX 1: Schedule of 
Assessments; Table 13), Section 
10.2.8. (Protocol Deviations) 
Addition of Part 1C-2 
Added to assess the heterologous or 
mixed series COVID-19 vaccine in 
this population  
Section 1.3.3. (Overall Benefit/Risk 
Conclusion), Section 2. (Objectives 
and Endpoints), Section 3.1. (General 
Design), Section 3.1.2. (Part 2 Study 
Design), Section 3.2. (Scientific 
Rationale for Study Design), Section 
3.3. (Justification for Dose, Control 
Product, and Choice of Study 
Population), Section 3.4. (End-of-
Study Definition), Section 4.1. 
(Eligibility Criteria [Part 1A and Part 
2]), Section 4.6. (Screen Failures 
[Part 1A: Blinded Phase and Part 2]), 
Added Part 2 where participants 
will get a 50 µg primary series 
and BD  
Changes made to test a lower dosing 
regimen to test safety and efficacy 

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Section Number and Name 
Description of Change 
Brief Rationale 
Section 5.1. (Investigational Product 
Administered), Section 5.3.1 
(Administration of Study Vaccine) 
Section 5.3.2. (Administration of 
Study Vaccine), Section 5.3.4. 
(Study Vaccine Packaging and 
Labeling), Section 5.4. (Study 
Treatment Compliance), Section 6.4. 
(Study Pause Rules), Section 7. 
(Study Assessments and Procedures), 
Section 7.1. (Safety Assessments and 
Procedures), Section 7.1.1. (Use of 
Electronic Diaries), Section 7.1.2. 
(Safety Telephone Calls), Section 
7.1.4. (Vital Sign Measurements), 
Section 7.1.5. (Physical 
Examinations), Section 7.1.6. 
(Assessment for SARS-CoV-2 
Infection), Section 7.2. 
(Immunogenicity Assessments), 
Section 7.5.7. (Eliciting and 
Documenting Adverse Events), 
Section 8.2.2. (Part 2), Section 
8.2.2.1. (Justification of Using 
Immunogenicity Subset of Adults 
(≥18 Years of Age) from Study P301 
as the Comparator for Part 2 
Hypothesis testing), Section 8.3.2. 
(Part 2), Section 8.5.7. (Part 2 
Analysis), Section 8.7.1. (Interim 
Analyses), Section 10.1. 
(APPENDIX 1: Schedule of 
Assessments, Table 14), Section 
10.2.8. (Protocol Deviations) 
Section 5.3.4. (Study Vaccine 
Packaging and Labeling) 
Updated vial information for 
investigational product for Part 
1C and Part 2 
Changes made to reflect current 
investigational product availability 
Section 7.1.6. (Assessment for 
SARS-CoV-2 Infection) 
Added information about 
restrictions due to Severe Acute 
Respiratory Syndrome 
coronavirus 2 related surges 
Changes made to allow for flexibility 
due to COVID-19 related restrictions 
Section 7.10. (Biomarkers) 
Changed that biomarkers are not 
evaluated in the study to that they 
will be stored for future 
assessment 
Changes made to allow for further 
testing as the landscape changes 
Section 8.6. (Multiplicity 
Adjustment) 
Added section to define the 
multiplicity adjustment with the 
multiple parts 
Changes made to clarify procedure to 
preserve the family-wise type I error 
rate 

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Amendment 3, 04 Nov 2021 
Main Rationale for the Amendment: 
To provide a 50 μg BD of mRNA-1273 to participants. This change is prompted by new interim 
data from an ongoing Moderna Phase 2 study, mRNA-1273-P201 (Study P201). Adult 
participants in Study mRNA-1273-P201 received 2 doses of either 50 μg or 100 μg of 
mRNA-1273 and were administered a 50 μg booster of mRNA-1273 6 to 8 months after the 
second dose. Participants in mRNA-1273-P201 who received the BD, demonstrated enhanced 
immune responses to SARS-CoV-2 compared to preboost levels and met the noninferiority 
criteria stipulated in the USA FDA Guidance on EUA for Vaccines to Prevent COVID-19. 
Additionally, no new safety signals emerged upon administration of the BD in Study P201. 
Based on cumulative evidence, the benefit-risk profile of a BD of mRNA-1273 is favorable, 
particularly in light of increasing breakthrough disease with the emergence of the Delta variant. 
Providing the option for a BD to all eligible participants currently enrolled is expected to 
generate valuable booster data in the adolescent population. 
Summary of Major Changes in Protocol Amendment 3: 
The Summary of Changes table provided below describes the major changes made in Protocol 
Amendment 3 relative to Protocol Amendment 2, including the sections modified and the 
corresponding rationales. The synopsis of Protocol Amendment 3 has been modified to 
correspond to changes in the body of the protocol. Minor grammar and formatting corrections 
were made throughout the document to enhance clarity and readability (which did not affect the 
conduct of the study). 
Section Number and Name 
Description of Change 
Brief Rationale 
Title Page, Signature page, Protocol 
Amendment Summary of Changes, 
and Header 
Updated the protocol version and 
date. 
Updated to reflect the new version 
and date. 
Synopsis, Section 4 (Study 
Population [Part A: Blinded Phase 
and Part B: Open-Label 
Observational Phase]) 
Updated the estimated date last 
participant completed and total 
number of sites. 
Changes made to reflect the 
confirmation of study sites and 
updated participant timeline. 
Synopsis, Section 3.1 (General 
Design) 
Extended the study duration.  
Changes made to reflect the addition 
of a new study part (Part C). 
Synopsis, Section 2 (Objectives and 
Endpoints) 
Added exploratory objectives for 
Part B.  
Changes made to reflect the planned 
analyses.  
Added primary, key secondary, 
and exploratory objectives for 
Part C. 
Changes made to reflect the addition 
of a new study part (Part C). 
Synopsis, Section 1.3.2 (Risks to 
Study Participants and Risk 
Mitigation), Section 1.3.3 (Overall 
Benefit/Risk Conclusion), Section 2 
(Objectives and Endpoints), Section 
3.1 (General Design), Section 3.1.3 
(Part C, Booster Dose Phase), 
Section 3.2 (Scientific Rationale for 
Study Design), Section 3.3 
Part C is being added to Study 
P203. 
Part C evaluates the safety and 
immunogenicity of a third BD of 
50 µg of mRNA-1273 in 
adolescents who have previously 
received 2 doses of mRNA-1273 
as a primary series.  
Changes made to reflect the addition 
of a new study part (Part C) to 
continue to evaluate the benefit-risk 
profile of a BD of mRNA-1273. 

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Section Number and Name 
Description of Change 
Brief Rationale 
(Justification for Dose, Control 
Product, and Choice of Study 
Population), Section 4.3 (Study 
Eligibility Criteria [Part C]), 
Section 5.1 (Investigational Product 
Administered), Section 5.3.1 
(Preparation of Study Vaccine for 
Injection), Section 5.3.2 
(Administration of Study Vaccine), 
Section 5.3.4 (Study Vaccine 
Packaging and Labeling), Section 5.4 
(Study Treatment Compliance), 
Section 6.4 (Study Pause Rules), 
Section 7 (Study Assessments and 
Procedures), Section 7.1 (Safety 
Assessments and Procedures), 
Section 7.1.1 (Use of Electronic 
Diaries), Section 8.1 (Blinding and 
Responsibility for Analyses), 
Section 8.2 (Statistical Hypothesis), 
Section 8.3 (Power and Sample 
Size), Section 8.5 (Statistical 
Methods), Section 10.1 (APPENDIX 
1: Schedule of Events; Table 10), 
Section 10.2.8 (Protocol Deviations) 
Synopsis, Section 3.1.1 (Part A, the 
Blinded Phase), Section 3.1.2 (Part 
B, the Open-label Observational 
Phase), Section 3.2 (Scientific 
Rationale for Study Design), Section 
7.1.6 (Assessment for SARS-CoV-2 
Infection), Section 7.3 (Exploratory 
Assessments and Biomarkers), 
Section 7.4.1 (Vaccine Effectiveness 
Assessments), Section 7.4.2 
(Surveillance for COVID-19 
Symptoms), Section 7.4.3 (Follow-
up/Convalescent Period After 
Diagnosis with COVID-19), 
Section 10.1 (APPENDIX 1: 
Schedule of Assessments, Table 7, 
Table 8, Table 9, Table 10) 
Add nasal swab to 
nasopharyngeal at all timepoints. 
To align with the original unblinding 
plan.  
Synopsis, Section 5.3.1 (Preparation 
of Study Vaccine for Injection), 
Section 5.3.2 (Administration of 
Study Vaccine), Section 5.3.4 (Study 
Vaccine Packaging and Labeling) 
Part C language was added to 
discuss the difference in volume. 
Changes made to reflect different 
vaccine volumes given during the 
primary series and the boost.  
Synopsis, Section 7.3 (Exploratory 
Assessments and Biomarkers) 
Addition of Exploratory 
Assessments and Biomarkers. 
To align language with other clinical 
studies. 
Synopsis, Section 8.5.5 (Long-term 
Analysis [including Part B]), Section 
Updated long-term analysis and 
Booster Phase analysis. 
Changes made to reflect the addition 
of a BD. 

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Section Number and Name 
Description of Change 
Brief Rationale 
8.5.6 (Booster Phase Analysis [Part 
C]) 
Synopsis, Section 8.6.1 (Interim 
Analyses) 
Addition of booster IAs. 
Changes made to reflect the addition 
of a BD. 
Section 1.1 (Study Rationale), 
Section 1.2.2 (Clinical Studies) 
Added updated clinical 
information of mRNA-1273. 
Changes made to reflect new and 
ongoing clinical data in the current 
and other studies. 
Section (5.3.5) Study Vaccine 
Storage 
Updated storage conditions to 
follow the investigational product 
label. 
Changes made to reflect differences 
in storage conditions between 
different vial volumes. 
Section 5.5.4 (Concomitant 
Medications and Vaccines that May 
Lead to the Elimination of a 
Participant from Per-Protocol 
Analyses) 
Added receipt or planned receipt 
of a nonstudy COVID-19 would 
require withdrawal from the 
study. 
To clarify that participants could not 
get other COVID-19 vaccines. 
Section 6.1.1 (Individual Participant 
Criteria for Delay of Study 
Vaccination) 
Added investigator judgment to 
rescheduling of visits. 
To allow for flexibility of visits. 
Section 7.1.6 (Assessment for 
SARS-CoV-2 Infection), Section 
7.4.2 (Surveillance for COVID-19 
Symptoms), Section 7.4.3 (Follow-
up/Convalescent Period After 
Diagnosis with COVID-19), Section 
10.1 (APPENDIX 1 Schedule of 
Events; Table 9) 
Added nasal swab for samples for 
SARS-CoV-2. 
To allow more flexibility for 
participants.  
Section 8.5.3 (Immunogenicity 
Analysis) 
Added the primary 
immunogenicity analysis is 
performed in Part A and Part C. 
To clarify that only Part A and Part C 
will have primary immunogenicity 
analyses. 
Amendment 2, 27 Jul 2021 
Main Rationale for the Amendment: 
The main rationale for this amendment is to increase awareness of possible cases and to add a 
case definition for myocarditis and pericarditis as well as guidance for reporting and assessing 
suspected cases for this study, given the recent reports in the EUA experience of cases with a 
temporal association between COVID-19 mRNA vaccine administration and signs and 
symptoms of myocarditis and pericarditis. 
Summary of Major Changes in Protocol Amendment 2: 
The Summary of Changes table provided below describes the major changes made in Protocol 
Amendment 2 relative to Protocol Amendment 1, including the sections modified and the 
corresponding rationales. The synopsis of Protocol Amendment 2 has been modified to 
correspond to changes in the body of the protocol. Minor grammar and formatting corrections 
were made throughout the document to enhance clarity and readability, and new references were 
added in support of the definition of myocarditis and pericarditis (which did not affect the 
conduct of the study). 

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Section Number and Name 
Description of Change 
Brief Rationale 
Title Page, Signature page, Protocol 
Amendment Summary of Changes, 
and Header 
• Updated the protocol version 
and date. 
• Added Protocol Amendment 
Summary of Changes for 
Amendment 2. 
Updated to reflect the new version 
and date. 
Section 1.3.2 (Risks to Study 
Participation and Risk Mitigation) 
Added paragraph on rare reports of 
myocarditis and pericarditis 
occurring after vaccination with 
Moderna coronavirus disease 2019 
(COVID-19) vaccine under EUA in 
adults 18 years of age and older. 
To reflect addendum made to 
Investigator’s Brochure. 
Section 7.4.5 (Adverse Events of 
Special Interest) 
Added CDC case definitions for 
myocarditis and pericarditis. 
To provide guidance to the 
investigators regarding assessing and 
reporting myocarditis and 
pericarditis for this study population. 
Section 7.5.2 (Independent Cardiac 
Event Adjudication Committee) 
Added new section. 
To describe the proposed mechanism 
to assess risk of myocarditis and 
pericarditis in the study population 
(to address CBER request to describe 
how the risk of myocarditis and 
pericarditis will be assessed in the 
study population receiving 
mRNA-1273). 
Section 8.1 (Blinding and 
Responsibility for Analyses) and 
Section 8.6.1 (Interim Analysis) 
Updated these sections to align 
with the revised SAP V2.0, which 
states the IA will be performed for 
immunogenicity, safety, and 
efficacy. 
To align with the updated SAP. 
Section 9 (References) 
Updated reference list. 
To support the text added to the 
protocol for myocarditis and 
pericarditis. 
Appendix 1, Schedule of 
Assessments, Table 7, and Table 9 
Increased D209 Participant 
Decision Visit window to -56/+56. 
Minus window expanded to 
accommodate participants whose 
D209 Visit is expected to occur after 
EUA is granted in this age group. 
Appendix 1, Schedule of 
Assessments, Table 9 
New footnote was added. 
To clarify that D209/Participant 
Decision Visit may occur over 
multiple visits but must be 
completed within 7 days. 
Section 10.4 (Appendix 4: Adverse 
Event of Special Interest Terms) 
Added new appendix to the 
protocol. 
To include AESI list in the protocol 
instead of as a separate document. 
Section 10.5 (Appendix 5: Protocol 
Amendment History) 
Moved the Summary of Changes 
for Protocol Amendment 1 to 
Appendix 5: Protocol Amendment 
History. 
To reflect the Summary of Changes 
for the new version of the 
amendment. 

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Amendment 1, 23 Mar 2021 
Main Rationale for the Amendment: 
The primary rationales for this amendment are as follows: 
• To update the primary endpoints and null hypotheses (or success criteria) for establishing 
immunobridging and assumptions for the sample size calculations, as recommended by 
health authorities. 
•  Following the authorization of a COVID-19 vaccine under an EUA, this study 
amendment is designed to transition to Part B, the Open-Label Observational Phase. 
Transitioning the study to Part B, the Open-label Observational Phase permits all ongoing 
study participants (a) to be informed of the availability and eligibility criteria of any 
COVID-19 vaccine made available under an EUA and (b) for EUA-eligible study 
participants, the opportunity to schedule a study visit to know their original group 
assignment (placebo versus mRNA-1273). 
• Part B, the Open-label Observational Phase also provides the opportunity for study 
participants who previously received placebo to request to receive 2 doses of the 
mRNA-1273 vaccine. 
The Summary of Changes table provided here describes the major changes made in Protocol 
Amendment 1 relative to the original protocol, including the sections modified and the 
corresponding rationales. The synopsis of Protocol Amendment 1 has been modified to 
correspond to changes in the body of the protocol. 
Summary of Major Changes in Protocol Amendment 1: 
Section Number and Name 
Description of Change 
Brief Rationale 
Title Page, Protocol Approval Page, 
Headers, Protocol Amendment 
Summary of Changes 
Updated the protocol version and 
date. 
To reflect the new version and date 
of the protocol. 
Protocol Synopsis – Objectives and 
Section 2 (Objectives and 
Endpoints) 
The primary endpoints were 
redefined. Secondary and 
exploratory endpoints were 
refined. An additional secondary 
objective and corresponding 
endpoint were added. A new 
exploratory objective and endpoint 
were added.  
If an accepted threshold of 
protection is not available, using 
coprimary endpoints based on nAb 
geometric mean and SRR (added) in 
the noninferiority test was 
recommended by health authorities, 
as it is considered standard in 
immunobridging. A secondary 
objective/endpoint to evaluate 
asymptomatic SARS-CoV-2 
infection was added to be separate 
from the objective/endpoint of 
SARS-CoV-2 infection in 
participants with SARS-CoV-2 
negative at baseline. An exploratory 
objective/endpoint was added to 
evaluate asymptomatic SARS-CoV-
2 infection in participants 
seropositive at baseline. 

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Section Number and Name 
Description of Change 
Brief Rationale 
Protocol Synopsis – Overall Study 
Design, Section 3.1 (General Study 
Design), Section 3.1.1 (Part A, the 
Blinded Phase), Section 3.1.2 (Part 
B, the Open-label Observational 
Phase), and Section 7 (Study 
Assessments and Procedures) 
The study design was updated to 
describe the updated crossover 
design of the study, including 
Part A (the Blinded Phase) and 
Part B (the Open-label 
Observational Phase).  
The addition of the crossover design 
provides the opportunity for study 
participants to be informed regarding 
the EUA of mRNA-1273 for any 
persons under the age of 18 years, be 
unblinded to their original 
assignment (mRNA-1273 or 
placebo), and for those who 
previously received placebo to 
actively request to receive 2 doses of 
mRNA-1273 (100 µg) vaccine.  
Protocol Synopsis – Study Duration 
and Section 3.1.1 (Part A, the 
Blinded Phase) 
The study duration was clarified to 
reflect the differing study duration 
for participants who were initially 
randomly assigned to mRNA-1273 
versus patients who were initially 
randomized to placebo but who 
opt to receive mRNA-1273 after 
unblinding. 
The addition of the crossover design 
was one of the primary purposes of 
this amendment.  
Protocol Synopsis – Inclusion 
Criteria and Section 4.1.1 (Inclusion 
Criteria) 
Updated to allow abstinence as a 
contraception option and remove 
the criteria that participants not be 
currently breastfeeding. 
Updated to be consistent with the 
current standard of care in the USA.  
Protocol Synopsis – Exclusion 
Criteria and Section 4.1.2 (Exclusion 
Criteria) 
Updated to remove exclusion of 
participants with a known history 
of SARS-CoV-2 infection or 
contact with a confirmed case of 
SARS-CoV-2 infection. 
Updated to be consistent with the 
current standard of care in the USA, 
and to address the increasing 
prevalence of SARS-CoV-2 
infection and make the study more 
consistent with the "real world" 
(EUA) setting. 
Protocol Synopsis – Study Eligibility 
Criteria (Part B) and Section 4.2 
(Study Eligibility Criteria, Part B) 
Section added for Part B of the 
study to specify that participants 
participating in Part B must have 
been previously enrolled in the 
mRNA-1273-P203 study; and that 
female participants of childbearing 
potential may enroll in Part B if 
they have negative pregnancy tests 
at OL-Day 1 and OL-Day 29. 
To establish separate eligibility 
criteria for Part B of the study. 
Protocol Synopsis – Procedures and 
Assessments (Safety Assessments) 
and Section 7.1 (Safety Assessments 
and Procedures) 
Updated to clarify the collection 
periods for ARs, AEs leading to 
discontinuation from dosing and/or 
study participation, MAAEs, 
SAEs, and AESIs. 
To clarify based on the new 
crossover design of the study. 
Protocol Synopsis – Procedures and 
Assessments (Immunogenicity 
Assessments) and Section 7.2 
(Immunogenicity Assessments) 
Updated to note the assessments 
for Part A and Part B of the study, 
to clarify the analytes to be 
measured, and to add testing of 
serum for nAb and bAb against the 
SARS-CoV-2 S protein. 
Revised the assessments and tests 
plan for the unbinding or Participant 
Decision Visit and subsequent visits 
to be used for long-term follow-up 
analyses. 

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Section Number and Name 
Description of Change 
Brief Rationale 
Protocol Synopsis – Procedures and 
Assessments (Efficacy Assessments) 
and Section 7.3.1 (Vaccine 
Effectiveness Assessments) 
Updated to refine the Ab response 
assessment if an accepted 
threshold of protection is not 
available.  
To define the coprimary endpoints 
required for the noninferiority test to 
establish immunobridging. 
Protocol Synopsis – Statistical 
Methods (Hypothesis Testing) and 
Section 8.2 (Statistical Hypothesis)  
Updated to redefine the study 
hypotheses based on updates to the 
coprimary endpoints.  
To specify the hypotheses for the 
updated coprimary endpoints using 
noninferiority test. 
Protocol Synopsis – Statistical 
Methods (Power and Sample Size) 
and Section 8.3 (Power and Sample 
Size) 
Updated to reflect increases in the 
size of the Immunogenicity Subset 
for the purposes of establishing 
acceptable noninferiority margins. 
To detail the sample size and power 
calculations for the updated primary 
endpoints and hypotheses. 
Protocol Synopsis – Statistical 
Methods (Analysis Sets) and Section 
8.4 (Analysis Sets) 
Added mITT and miTT1 analysis 
sets. 
To define mITT and mITT1 to be 
used in the sensitivity analyses of 
secondary efficacy endpoints. 
Protocol Synopsis – Statistical 
Methods (Immunogenicity 
Analyses) and Section 8.5.3 
(Immunogenicity Analyses) 
Updated the analyses of the 
coprimary endpoints. 
To describe the analysis methods for 
the updated coprimary endpoints. 
Protocol Synopsis – Statistical 
Methods (Efficacy Analyses) and 
Section 8.5.4 (Efficacy Analyses) 
Updated to clarify the secondary 
efficacy analyses.  
To clarify the secondary efficacy 
analyses. 
Protocol Synopsis – Statistical 
Methods (Long-term Analysis) and 
Section 8.5.5 (Long-term Analysis) 
Added section to describe 
long-term analyses of safety, 
efficacy, and immunogenicity data 
to include data collected during 
Part B of the study.  
To describe long-term analyses 
including Part B data. 
Protocol Synopsis – Study Analyses 
(Interim Analyses) and Section 8.6.1 
(Interim Analyses) 
Updated to indicate that more than 
one IA may be performed, and to 
describe the timepoints at which 
the analyses will be performed.  
To support potential EUA in the 
adolescent age group. 
Section 1.2.2 (Clinical Studies) 
Revised section to provide data for 
ongoing mRNA-1273 studies. 
To harmonize section content with 
current status of development in the 
program.  
Section 1.3.2 (Risks from Study 
Participation and Their Mitigation), 
3.1.1 (Part A, the Blinded Phase), 
5.3.2 (Administration of Study 
Vaccine), 7.1.1 (Use of Electronic 
Diaries), and 7.1.4 (Vital Sign 
Measurements) 
Updated postIP administration 
observation period from 
60 minutes to 30 minutes. 
Pursuant to cross-functional 
discussion and observation period of 
15 minutes under the EUA. 
Section 3.3 (Justification for Dose, 
Control Product, and Choice of 
Study Population) 
Updated section to include 
justification for the crossover 
design. 
The addition of the crossover design 
was one of the primary purposes of 
this amendment. 
Section 5.3.2 (Administration of 
Study Vaccine) 
Updated IP administration to 
include the IP administered in Part 
A and Part B of the study.  
The addition of the crossover design 
was one of the primary purposes of 
this amendment. 

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mRNA-1273-P203 Protocol Amendment 7 
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Section Number and Name 
Description of Change 
Brief Rationale 
Section 6.2 (Discontinuing Study 
Vaccination) 
Updated to remove the allowance 
for study removal for serology or 
RT-PCR testing positive for 
SARS-CoV2 for either Day 1 or 
for an illness visit. 
Updated to be consistent with 
current standard of care in the USA.  
Section 6.4 (Study Pause Rules) 
Updated to clarify that study pause 
rules are only applicable to Part A 
of the study but that participants 
will be monitored for the events 
leading to study pause during 
Part B of the study. Updated to 
clarify actions to be taken if 
thresholds for any pause rules are 
met. 
Updated to clarify that any 
Grade 3 or higher AEs meet event 
criteria. 
To clarify safety assessments after 
crossover. 
Section 7.1.1. (Use of Electronic 
Diaries) 
Updated to clarify that eDiaries 
will only be used in Part A of the 
study.  
The solicited AR profile will be 
sufficiently demonstrated in Part A; 
therefore, it is no longer necessary to 
collect additional data on solicited 
ARs following injection in the open-
label phase.  
Section 7.3.1 (Vaccine Effectiveness 
Assessments) 
Updated to further define criteria 
for SARS-CoV-2 infection.  
To clarify the definition of 
SARS-CoV-2 infection in 
participants who are SARS-CoV-2 
negative at baseline. 
Section 7.4.4.1 (Anaphylaxis) 
Added section to characterize 
anaphylaxis and provide reporting 
requirements.  
This text is being added to all 
mRNA-1273 protocols based on 
recent reports of anaphylaxis in the 
postEUA setting. 
Section 7.4.5 (Adverse Events of 
Special Interest) 
Updated to define an AESI and 
provide reporting requirements. 
To provide more specific guidance 
to sites. 
Section 7.4.7 (Eliciting and 
Documenting Adverse Events) 
Updated to clarify that solicited 
ARs will be collected only in 
Part A, and to define the end-of-
study participation for the 
purposes of collection MAAEs and 
SAEs. 
To provide more specific guidance 
to sites. 
Section 8.1 (Blinding and 
Responsibility for Analyses) 
Updated to describe unblinding 
procedures relevant to the interim 
analyses.  
To clarify the blinding/unblinding 
plan and process. 
Section 10.1 (Appendix 1: Schedule 
of Assessments) 
Table 7 title updated to reflect Part 
A of the study. 
Updated study visit day 209 to 
“Day 209/Participant Decision 
Visit” 
To clarify as related to crossover 
design. 

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mRNA-1273-P203 Protocol Amendment 7 
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Page 224 
Section Number and Name 
Description of Change 
Brief Rationale 
Increased visit window for Day 
209 to ±56 days. 
Increased visit window for the 
safety follow-ups (Day 223-Day 
363) to ±3 days. 
Row added for revised informed 
consent/assent form. 
Added note to clarify the SoA to 
be followed after unblinding for 
participants who previously 
received mRNA-1273. 
Added footnote for time frame for 
Participant Decision Clinic Visit. 
Revised footnote to indicate that 
eDiary recording will start 
approximately 30 minutes after 
injection. 
Added table (Table 8) for the 
Participant Decision Clinic Visit. 
To allow for participant unblinding 
and decision to receive mRNA-1273 
if previously randomized to placebo. 
Added new SoA (Table 9) for 
Part B of the study.  
To provide instructions for 
participants previously randomized 
to placebo who have elected to 
receive mRNA-1273 in Part B of the 
study.  
Added flow chart (Figure 4) 
between Part A and Part B of the 
study. 
To demonstrate participants’ 
movement between Part A and 
Part B, and back to Part A.  
Section 10.2.8 (Protocol Deviations) 
Added guidance for participants’ 
movement between Part A and 
Part B. 
The addition of the crossover design 
was one of the primary purposes of 
this amendment. 
Abbreviations: AESI = adverse event of special interest; AR = adverse reaction; bAb = binding antibody; 
CBER = Center for Biologics Evaluation and Research; D = day; eDiary = electronic diary; EUA = Emergency 
Use Authorization; IP = investigational product; MAAE = medically attended adverse event; mITT = modified 
intent-to-treat; nAb = neutralizing antibody; SAE = serious adverse event; RT-PCR = reverse transcriptase 
polymerase chain reaction; SARS-CoV2 = Severe Acute Respiratory Syndrome coronavirus 2; SoA = Schedule of 
Assessments. 

Signature Page for VV-CLIN-003517 v11.0
Signature Page for VV-CLIN-003517 v11.0
2nd Approval
23-Oct-2023 18:08:40 GMT+0000
PPD