A Phase 2, Two-Part Study (Open-Label [Part 1] Followed by Observer-Blind/Randomized [Part 2]) to Evaluate the Safety, Tolerability, Reactogenicity, and Effectiveness of mRNA-1273.214 SARS-CoV-2 Vaccine in Participants Aged 12 Weeks to < 6 Months
Phase: PHASE2
Conditions: SARS-CoV-2
Sponsor: ModernaTX, Inc.

ModernaTX, Inc. 
mRNA-1273.214 
Protocol: mRNA-1273-P206, Original 
 
 
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CLINICAL STUDY PROTOCOL 
Protocol Title: 
A Phase 2, Two-Part Study (Open-Label [Part 1] Followed by 
Observer-Blind/Randomized [Part 2]) to Evaluate the Safety, 
Tolerability, Reactogenicity, and Effectiveness of 
mRNA-1273.214 SARS-CoV-2 Vaccine in Participants Aged 
12 Weeks to < 6 Months 
Protocol Number: 
mRNA-1273-P206 (BabyCOVE) 
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: 
IND: 019745 
Date of Original Protocol: 
17 Jun 2022 
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. 
 
PPD
PPD
PPD
PPD

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PROTOCOL APPROVAL – SPONSOR SIGNATORY 
Study Title: 
A Phase 2, Two-Part Study (Open-Label [Part 1] Followed by 
Observer-Blind/Randomized [Part 2]) to Evaluate the Safety, 
Tolerability, Reactogenicity, and Effectiveness of mRNA-1273.214 
SARS-CoV-2 Vaccine in Participants Aged 12 Weeks to < 6 Months 
Protocol Number: 
mRNA-1273-P206 (BabyCOVE) 
Date of Original 
Protocol: 
17 Jun 2022 
 
Protocol accepted and approved by: 
See eSignature and date signed  
on last page of the document 
 
 
 
ModernaTX, Inc. 
200 Technology Square 
Cambridge, MA 02139 
Telephone:
 
 
 
Date 
 
 
 
 
 
 
PPD
PPD

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DECLARATION OF INVESTIGATOR 
I have read and understood all sections of the protocol entitled “A Phase 2, Two-Part Study 
(Open-Label [Part 1] Followed by Observer-Blind/Randomized [Part 2]) to Evaluate the Safety, 
Tolerability, Reactogenicity, and Effectiveness of mRNA-1273.214 SARS-CoV-2 Vaccine in 
Participants Aged 12 Weeks to < 6 Months,” 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 institutional review board (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 subinvestigator. 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 
 
 
 

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TABLE OF CONTENTS 
 
CLINICAL STUDY PROTOCOL ..................................................................................................1 
PROTOCOL APPROVAL – SPONSOR SIGNATORY ................................................................2 
DECLARATION OF INVESTIGATOR .........................................................................................3 
TABLE OF CONTENTS .................................................................................................................4 
LIST OF TABLES ...........................................................................................................................9 
LIST OF FIGURES .........................................................................................................................9 
LIST OF ABBREVIATIONS ........................................................................................................10 
1. 
PROTOCOL SUMMARY ..........................................................................................13 
1.1. 
Protocol Synopsis .......................................................................................................13 
1.2. 
Study Schema .............................................................................................................29 
1.3. 
Schedule of Assessments ............................................................................................30 
2. 
INTRODUCTION ......................................................................................................34 
2.1. 
Study Rationale ...........................................................................................................34 
2.2. 
Background and Overview .........................................................................................34 
2.2.1. 
Nonclinical Studies .....................................................................................................37 
2.2.2. 
Clinical Studies ...........................................................................................................37 
2.3. 
Benefit/Risk Assessment ............................................................................................38 
2.3.1. 
Known Potential Benefits ...........................................................................................38 
2.3.2. 
Risks From Study Participation and Their Mitigation ................................................38 
2.3.3. 
Overall Benefit/Risk Conclusion ................................................................................40 
3. 
OBJECTIVES AND ENDPOINTS ............................................................................42 
4. 
STUDY DESIGN .......................................................................................................46 
4.1. 
General Design ...........................................................................................................46 
4.1.1. 
Study Periods ..............................................................................................................47 
4.2. 
Scientific Rationale for Study Design ........................................................................48 
4.3. 
Justification for Dose, Control Product, and Choice of Study Population .................49 
4.4. 
End of Study Definition ..............................................................................................50 
5. 
STUDY POPULATION .............................................................................................51 
5.1. 
Inclusion Criteria ........................................................................................................51 
5.2. 
Exclusion Criteria .......................................................................................................51 

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5.3. 
Screen Failures ............................................................................................................53 
6. 
STUDY TREATMENT ..............................................................................................55 
6.1. 
Investigational Products Administered .......................................................................55 
6.2. 
Randomization and Blinding ......................................................................................55 
6.3. 
Preparation/Handling/Storage/Accountability ............................................................56 
6.3.1. 
Clinical Study Material Preparation ...........................................................................56 
6.3.2. 
Clinical Study Material Administration......................................................................56 
6.3.3. 
Clinical Study Material Delivery and Receipt ............................................................57 
6.3.4. 
Clinical Study Material Packaging and Labeling .......................................................57 
6.3.5. 
Clinical Study Material Storage ..................................................................................57 
6.3.6. 
Clinical Study Material Accountability ......................................................................57 
6.3.7. 
Clinical Study Material Handling and Disposal .........................................................58 
6.3.8. 
Unblinding ..................................................................................................................58 
6.4. 
Study Treatment Compliance .....................................................................................58 
6.5. 
Prior and Concomitant Medications ...........................................................................59 
6.5.1. 
Maternal Medications and Therapies ..........................................................................59 
6.5.2. 
Prior Medications and Therapies ................................................................................59 
6.5.3. 
Concomitant Medications and Therapies ...................................................................59 
6.5.4. 
Concomitant Medications and Vaccines That May Lead to the Elimination of 
a Participant from Per-protocol Analyses ....................................................................60 
7. 
DELAY OR DISCONTINUATION OF STUDY INTERVENTION AND 
PARTICIPANT DISCONTINUATION/WITHDRAWAL .......................................62 
7.1. 
Criteria for Delay of Vaccine Administration ............................................................62 
7.1.1. 
Individual Participant Criteria for Delay of Study Vaccination ...................................62 
7.2. 
Discontinuation of Study Vaccination ........................................................................63 
7.3. 
Participant Discontinuation/Withdrawal From the Study ...........................................64 
7.3.1. 
End-of-study Visit (Prior to Day 422) .........................................................................65 
7.4. 
Study Pause Rules.......................................................................................................65 
7.5. 
Lost to Follow-up .......................................................................................................67 
8. 
STUDY ASSESSMENTS AND PROCEDURES ......................................................68 
8.1. 
Screening ....................................................................................................................68 
8.2. 
Confirm Inclusion and Exclusion Criteria ..................................................................68 
8.3. 
Demographic and Baseline Data ................................................................................69 

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8.4. 
Medical History ..........................................................................................................69 
8.5. 
Randomization ............................................................................................................69 
8.6. 
Physical Examination and Vital Signs ........................................................................69 
8.7. 
Study Vaccine Administration ....................................................................................70 
8.8. 
Immunogenicity Assessments ....................................................................................70 
8.9. 
Vaccine Effectiveness Assessments and Surveillance for COVID-19 
Symptoms ...................................................................................................................71 
8.9.1. 
Vaccine Effectiveness Assessments ............................................................................71 
8.9.2. 
COVID-19 Case Definitions .......................................................................................71 
8.9.3. 
Surveillance for COVID-19 Symptoms .......................................................................74 
8.9.4. 
Follow-up Period After Diagnosis With COVID-19 ...................................................79 
8.10. 
Safety Assessments .....................................................................................................79 
8.10.1. 
Safety Telephone Calls ................................................................................................79 
8.10.2. 
Use of Electronic Diaries .............................................................................................80 
8.10.3. 
Blood Sampling Volumes ...........................................................................................82 
8.10.4. 
Safety Laboratory Assessments ..................................................................................82 
8.10.5. 
Ancillary Supplies for Participant Use .......................................................................82 
8.11. 
Safety Definitions and Related Procedures ................................................................83 
8.11.1. 
Adverse Event .............................................................................................................83 
8.11.2. 
Serious Adverse Events ..............................................................................................83 
8.11.3. 
Solicited Adverse Reactions .......................................................................................85 
8.11.4. 
Medically Attended Adverse Events ..........................................................................87 
8.11.5. 
Adverse Events of Special Interest .............................................................................88 
8.11.6. 
Recording and Follow-up of an AE and/or SAE ........................................................89 
8.11.7. 
Assessment of Intensity ..............................................................................................90 
8.11.8. 
Assessment of Causality .............................................................................................90 
8.11.9. 
Reporting Adverse Events ..........................................................................................91 
8.11.10. 
Reporting SAEs ..........................................................................................................91 
8.11.11. 
Time Period and Frequency for Collecting AE, AESI, MAAE, and SAE 
Information .................................................................................................................92 
8.11.12. 
Method of Detecting AEs and SAEs ..........................................................................93 
8.11.13. 
Follow-up of AEs and SAEs .......................................................................................93 
8.11.14. 
Regulatory Reporting Requirements for SAEs ...........................................................93 

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8.12. 
Safety Oversight .........................................................................................................94 
8.12.1. 
Internal Safety Team ...................................................................................................94 
8.12.2. 
Data Safety Monitoring Board ....................................................................................94 
8.12.3. 
Cardiac Event Adjudication Committee .....................................................................95 
8.13. 
Treatment of Overdose ...............................................................................................95 
8.14. 
Pharmacokinetics ........................................................................................................95 
8.15. 
Pharmacodynamics .....................................................................................................95 
8.16. 
Biomarkers ..................................................................................................................95 
9. 
STATISTICAL ANALYSIS PLAN ...........................................................................96 
9.1. 
Blinding and Responsibility for Analyses ..................................................................96 
9.2. 
Statistical Hypotheses .................................................................................................97 
9.3. 
Sample Size and Power Calculation ...........................................................................98 
9.4. 
Analysis Populations ..................................................................................................99 
9.5. 
Statistical Analyses ...................................................................................................100 
9.5.1. 
Immunogenicity Analyses ........................................................................................100 
9.5.2. 
Safety Analyses ........................................................................................................102 
9.5.3. 
Exploratory Analyses ................................................................................................103 
9.5.4. 
Subgroup Analyses ...................................................................................................104 
9.6. 
Planned Analyses ......................................................................................................104 
9.6.1. 
Interim Analyses .......................................................................................................104 
9.6.2. 
Final Analysis ...........................................................................................................104 
10. 
REFERENCES .........................................................................................................105 
11. 
SUPPORTING DOCUMENTATION AND OPERATIONAL 
CONSIDERATIONS ................................................................................................110 
11.1. 
APPENDIX 1: Study Governance Considerations ...................................................111 
11.1.1. 
Regulatory and Ethical Considerations ....................................................................111 
11.1.2. 
Study Monitoring ......................................................................................................111 
11.1.3. 
Audits and Inspections ..............................................................................................113 
11.1.4. 
Financial Disclosure .................................................................................................113 
11.1.5. 
Recruitment Strategy ................................................................................................113 
11.1.6. 
Informed Consent Process ........................................................................................114 
11.1.7. 
Protocol Amendments ..............................................................................................115 

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11.1.8. 
Protocol Deviations ..................................................................................................115 
11.1.9. 
Data Protection .........................................................................................................116 
11.1.10. 
Sample Retention and Future Biomedical Research ................................................116 
11.1.11. 
Dissemination of Clinical Study Data ......................................................................117 
11.1.12. 
Data Quality Assurance and Quality Control ...........................................................117 
11.1.13. 
Data Collection and Management ............................................................................118 
11.1.14. 
Source Documents ....................................................................................................119 
11.1.15. 
Retention of Records ................................................................................................119 
11.1.16. 
Study and Site Closure..............................................................................................120 
11.1.17. 
Publication Policy .....................................................................................................120 
11.1.18. 
Height and Weight Chart for Boys and Girls ...........................................................122 
11.2. 
APPENDIX 2: Adverse Events of Special Interest Terms .......................................124 
11.3. 
APPENDIX 3: CDC Working Case Definitions of Pericarditis, Myocarditis, 
and Myopericarditis Occurring After Receipt of COVID-19 mRNA 
Vaccines ....................................................................................................................128 
 
 
 

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LIST OF TABLES 
Table 1: 
Schedule of Assessments (Part 1 and Part 2) ..............................................................30 
Table 2: 
Objectives and Endpoints for Part 1 ...........................................................................42 
Table 3: 
Objectives and Endpoints for Part 2 ...........................................................................43 
Table 4: 
Pause Rule Criteria, Events, and Thresholds ..............................................................66 
Table 5: 
Age-specific Cutoffs for Vital Signs and Laboratory Variables ................................72 
Table 6: 
Definition of Renal, Liver, and Neurological Dysfunction for Pediatric 
Population (< 12 years of age) ....................................................................................73 
Table 7: 
Solicited Adverse Reactions and Grades: Age 12 Weeks to < 6 Months ...................85 
Table 8: 
Populations for Analyses ............................................................................................99 
Table 9: 
Analysis Strategy for Safety Parameters ..................................................................103 
Table 10: Adverse Events of Special Interest ...........................................................................124 
Table 11: Case Definitions of Probable and Confirmed Myocarditis, Pericarditis, and 
Myopericarditis .........................................................................................................128 
LIST OF FIGURES 
Figure 1: 
Study Schema .............................................................................................................29 
Figure 2: 
Surveillance for COVID-19 Symptoms and the Corresponding Clinical Data 
Pathways .....................................................................................................................75 
 
 
 
 

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LIST OF ABBREVIATIONS 
The following abbreviations and terms are used in this study protocol. 
Abbreviation 
Definition 
Ab 
antibody 
AE 
adverse event 
AESI 
adverse event of special interest 
AR 
adverse reaction 
bAb 
binding antibody 
CDC 
Centers for Disease Control and Prevention 
CEAC 
cardiac event adjudication committee 
CFR 
Code of Federal Regulations 
CI 
confidence interval 
CLIA 
Clinical Laboratory Improvement Amendments 
CoV 
coronavirus 
COVID-19 
coronavirus disease 2019 
CRF 
case report form 
CRO 
contract research organization 
CSR 
clinical study report 
DSMB 
data safety monitoring board 
DTaP 
diphtheria, tetanus, and pertussis 
eCRF 
electronic case report form 
EDC 
electronic data capture 
eDiary 
electronic diary 
EoS 
end of study 
EUA 
Emergency Use Authorization 
FDA 
Food and Drug Administration 
GCP 
Good Clinical Practice 
GLSM 
geometric least square mean 
GM 
geometric mean 
GMR 
geometric mean titer ratio 
GMT 
geometric mean titer 
HCP 
healthcare practitioner 

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Abbreviation 
Definition 
Hib 
Haemophilus influenzae type b 
IB 
Investigator’s Brochure 
ICF 
informed consent form 
ICH 
International Council for Harmonisation 
ICU 
intensive care unit 
IST 
internal safety team 
IM 
intramuscular 
IP 
investigational product 
IPV 
inactivated poliovirus vaccine 
IRB 
institutional review board 
IRT 
interactive response technology 
LAR 
legally authorized representative 
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 
MMR 
measles, mumps, and rubella 
mRNA 
messenger ribonucleic acid 
NAAT 
Nucleic Acid Amplification Test 
nAb 
neutralizing antibody 
PCV13 
pneumococcal conjugate vaccine 
PEG 
polyethylene glycol 
PP 
per protocol 
PPIS-Neg 
Per-Protocol Immunogenicity Set – SARS-CoV-2 Negative 
QA 
quality assurance 
RT-PCR 
reverse transcription polymerase chain reaction 
SAE 
serious adverse event 
SAP 
statistical analysis plan 

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Abbreviation 
Definition 
SARS 
severe acute respiratory syndrome 
SARS-CoV 
severe acute respiratory syndrome coronavirus 
SARS-CoV-2 
severe acute respiratory syndrome coronavirus 2 
SM-102 
heptadecan-9-yl 8-{(2hydroxyethyl)[6-oxo-6-
(undecyloxy)hexyl]amino}octanoate 
SoA 
schedule of assessments 
SRR 
seroresponse rate 
S-2P 
spike protein modified with 2 proline substitutions within the heptad 
repeat 1 domain 
US 
United States 
VOC 
variants of concern 
WHO 
World Health Organization 
 
 

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1. 
PROTOCOL SUMMARY 
1.1. 
Protocol Synopsis 
Name of Sponsor/Company: ModernaTX, Inc. 
Name of Investigational Product: mRNA-1273.214 for injection 
Name of Active Ingredient: mRNA-1273.214 
Protocol Title: A Phase 2, Two-Part Study (Open-Label [Part 1] Followed by 
Observer-Blind/Randomized [Part 2]) to Evaluate the Safety, Tolerability, Reactogenicity, and 
Effectiveness of mRNA-1273.214 SARS-CoV-2 Vaccine in Participants Aged 12 Weeks to 
< 6 Months 
Protocol Number: mRNA-1273-P206 (BabyCOVE) 
Study Duration: Approximately 27 months 
Phase of Development: Phase 2 
Estimated Date First Participant Enrolled: 30 Sep 2022  
Estimated Date Last Participant Completed: 31 Mar 2025 
Proposed Countries: United States (US) 
Objectives and Endpoints 
Objectives and Endpoints for Part 1 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety and 
reactogenicity of 2 dose levels1 of 
mRNA-1273.214 vaccine 
administered as 2 doses 8 weeks 
apart in participants aged 12 weeks 
to < 6 months 
• 
Solicited local and systemic ARs through 7 days 
after each injection 
• 
Unsolicited AEs through 28 days after each 
injection 
• 
MAAEs throughout the entire study period 
• 
SAEs throughout the entire study period 
• 
AESIs throughout the entire study period 

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• 
AEs leading to discontinuation from study 
participation postdose throughout the entire study 
period 
Secondary Objectives 
Secondary Endpoints 
• 
To evaluate the immunogenicity of 
2 dose levels1 of mRNA-1273.214 
vaccine administered as 2 doses 
8 weeks apart in participants aged 
12 weeks to < 6 months 
• 
GMT of antibodies against SARS-CoV-2 VOC 
(Omicron) at 28 days after second dose 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; 
GMT = geometric mean titer; MAAE = medically attended adverse event; mRNA = messenger RNA; 
SAE = serious adverse event; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2; VOC = variants 
of concern. 
1. Dose levels of mRNA-1273.214 vaccine administered to participants will be 5 µg and 10 µg. 
Objectives and Endpoints for Part 2 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety and 
reactogenicity of selected dose level 
(from Part 1) of mRNA-1273.214 
vaccine administered as 2 doses 
8 weeks apart in participants aged 
12 weeks to < 6 months 
• 
Solicited local and systemic ARs through 7 days 
after each injection 
• 
Unsolicited AEs through 28 days after each 
injection 
• 
MAAEs throughout the entire study period 
• 
SAEs throughout the entire study period  
• 
AESIs throughout the entire study period 
• 
AEs leading to discontinuation from study 
participation postdose throughout the entire study 
period 
• 
To infer the effectiveness of 
selected dose level (from Part 1) of 
mRNA-1273.214 vaccine 
administered as 2 doses 8 weeks 
apart in participants aged 12 weeks 
to < 6 months 
• 
Co-primary Endpoint: GMT of antibodies against 
SARS-CoV-2 VOC (Omicron) at 28 days after the 
second dose of mRNA-1273.214 compared with 
that of the adult participants at Day 57 (28 days 
after the second dose) in Study mRNA-1273-P301 
dosed with mRNA-1273 (100 µg, 2 doses 28 days 
apart) primary series 
• 
Co-primary Endpoint: SRR1 against SARS-CoV-2 
VOC (Omicron) at 28 days after the second dose of 
mRNA-1273.214 compared with that of the adult 

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Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; 
GMT = geometric mean titer; LLOQ = lower limit of quantification; MAAE = medically attended adverse event; 
mRNA = messenger RNA; SAE = serious adverse event; SRR = seroresponse rate; SARS-CoV-2 = severe acute 
respiratory syndrome coronavirus 2; VOC = variants of concern. 
1. Seroresponse is defined as a titer change from baseline (pre-Dose 1) below the LLOQ to ≥ 4 × LLOQ, or at 
least a 4-fold rise if baseline is ≥ LLOQ. 
Refer to Section 3 for a complete listing of primary, secondary, and exploratory endpoints 
related to Part 1 and/or Part 2 of the study. 
participants at Day 57 (28 days after the second 
dose) in Study mRNA-1273-P301 dosed with 
mRNA-1273 (100 µg, 2 doses 28 days apart) 
primary series 
Secondary Objectives 
Secondary Endpoints 
• 
To evaluate the immune response 
against SARS-CoV-2 VOC 
(Omicron) elicited by 
mRNA-1273.214 vaccine 
administered as 2 doses 8 weeks 
apart in participants aged 12 weeks 
to < 6 months, compared with the 
immune responses against original 
strain induced by mRNA-1273 
primary series (100 µg, 2 doses 
28 days apart) 
• 
GMT of antibodies and SRR against SARS-CoV-2 
VOC (Omicron) at 28 days after the second dose of 
mRNA-1273.214 primary series, compared with 
GMT and SRR against original strain at Day 57 
(28 days after the second dose) in 
Study mRNA-1273-P301 dosed with mRNA-1273 
primary series 
• 
To evaluate the immune response 
against SARS-CoV-2 original strain 
elicited by mRNA-1273.214 vaccine 
administered as 2 doses 8 weeks 
apart in participants aged 12 weeks 
to < 6 months, compared with the 
immune responses against original 
strain induced by mRNA-1273 
primary series (100 µg, 2 doses 
28 days apart) 
• 
GMT of antibodies and SRR against SARS-CoV-2 
original strain at 28 days after the second dose of 
mRNA-1273.214 primary series, compared with 
GMT and SRR against original strain at Day 57 
(28 days after the second dose) in 
Study mRNA-1273-P301 dosed with mRNA-1273 
primary series 

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Overall Study Design 
This is a Phase 2, two-part, open-label in Part 1 and observer-blind, randomized, placebo-
controlled in Part 2 study to evaluate the safety, tolerability, reactogenicity, and effectiveness 
of mRNA-1273.214 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine 
in infants aged 12 weeks to < 6 months. 
The study will be conducted in 2 parts. Part 1 will consist of Arm 1 and Arm 2 that will enroll 
sequentially, ie, Arm 1 will begin enrollment and the periodic safety review will determine 
whether Arm 2 can begin enrollment. In Part 1, participants will receive 5 µg of 
mRNA-1273.214 in Arm 1 and 10 µg of mRNA-1273.214 in Arm 2. Arm 1 will start with 
2 doses of 5 µg (sentinel dosing) administered 8 weeks apart of up to 4 participants. An 
internal safety team (IST) will review safety data after Dose 1 (1 week after Dose 1 of mRNA-
1273.214) and provide a recommendation to further dose participants. Once safety and 
tolerability after Dose 1 have been reviewed by the IST, Arm 1 will continue enrollment for a 
total of 50 participants.  
The IST will reconvene once 25 participants in Arm 1 reach Day 64 (1 week after Dose 2 of 
5 µg administered 8 weeks apart). If no safety concerns are identified after IST review in 
Arm 1, Arm 2 will begin enrollment and participants will receive 2 doses of 10 µg of 
mRNA-1273.214 administered 8 weeks apart. Similar to Arm 1, safety and tolerability will be 
reviewed by the IST after 4 participants have received Dose 1 (1 week after Dose 1 of 
mRNA-1273.214) and again when 25 participants reach Day 64, and provide a 
recommendation for continuing dosing and enrollment at each review. Arm 2 will enroll a 
total of 50 participants. The immunogenicity and safety analysis will be conducted after all 
treated participants in both Arms 1 and 2 reach Day 85 (28 days from second dose). The 
results from Part 1 will determine the dose level for Part 2, which will be blinded and 
randomized. 
Part 2 of the study will consist of 2 groups (Arm 3 and Arm 4). In Part 2, study participants 
will be randomly assigned to receive mRNA-1273.214 (Arm 3), at the dose level selected 
from Part 1, or placebo (Arm 4). The immunogenicity and safety analysis will be conducted 
after all treated participants reach Day 85 (28 days from second dose). Participants will be 
followed for approximately 12 months after completion of the primary series.  
Number of Participants: A total of 100 participants (50 participants each in Arm 1 and 
Arm 2) will be enrolled in Part 1. In Part 2, a total of approximately 600 participants will be 
randomly assigned to receive mRNA-1273.214 (Arm 3) or placebo (Arm 4) in a 1:1 ratio 
(n = 300 per arm). 

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Target Population: Healthy infants aged 12 weeks to < 6 months at the time of consent, in 
both Part 1 and Part 2. 
Study Eligibility Criteria 
Inclusion Criteria:  
Participants are eligible to be included in the study only if all the following criteria apply: 
1. The participant is male or female, between 2 and < 6 months of age at the time of 
consent (Screening Visit), who is in good general health, in the opinion of the 
investigator, based on review of medical history and screening physical examination. 
a) Participant must be at least 12 weeks completed age and must not have 
completed 6 months at the time of administration of first dose.  
b) If the participant has a chronic, stable disease, they may be eligible to enroll in 
Part 2, but ineligible for Part 1. The chronic condition (eg, gastroesophageal 
reflux disease) should be stable, per investigator assessment, so that the 
participant can be considered eligible for inclusion in Part 2. Note: a change in 
medication for dose optimization, change within class of medication, reduction 
in dose or increase in dose due to expected weight gain are not considered signs 
of instability. 
2. The participant was born at ≥ 37 weeks gestation (Part 1) or ≥ 34 weeks gestation 
(Part 2), with a minimum birth weight of 2.5 kg, without fetal growth restriction, and 
the participant’s height and weight are both at or above the second percentile for age 
according to the Centers for Disease Control and Prevention (CDC)/World Health 
Organization Child Growth Standard at the Screening Visit. 
3. In the investigator’s opinion, the parent(s)/legally authorized representatives (LARs) 
understand and are willing and physically able to comply with protocol-mandated 
follow-up, including all procedures, and provide written informed consent. This 
includes inability to collect minimum amount of sample volume at baseline blood 
draw.  
Exclusion Criteria:  
Participants will be excluded from the study if any of the following criteria apply: 
1. The participant has a known history of symptomatic SARS-CoV-2 infection within 
2 weeks prior to administration of investigational product (IP) or has a known close 

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contact (as defined in Section 8.10.2) in the past 2 weeks to someone diagnosed with 
SARS-CoV-2 infection or coronavirus disease 2019 (COVID-19). Participants may be 
rescreened after 14 days provided that they remain asymptomatic. 
2. The participant is acutely ill or febrile 72 hours prior to or at the Screening Visit. 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. The participant has previously been administered an investigational or approved 
coronavirus (CoV) (eg, SARS-CoV-2, SARS-CoV, Middle East respiratory 
syndrome-CoV) vaccine. 
4. The participant has undergone treatment with investigational or approved agents for 
prophylaxis against COVID-19 (eg, receipt of SARS-CoV-2 monoclonal antibodies) 
within 90 days prior to enrollment. 
5. The participant has a known hypersensitivity to a component of the vaccine or its 
excipients. Hypersensitivity includes, but is not limited to, anaphylaxis or immediate 
allergic reaction of any severity to any of the components of messenger RNA (mRNA) 
COVID-19 vaccines (including polyethylene glycol or immediate allergic reaction of 
any severity to polysorbate). 
6. The participant has a medical, psychiatric, or occupational condition, including 
reported history of substance abuse, in the infant or in the parent(s)/LAR(s) that, 
according to the investigator’s judgment, may pose additional risk as a result of 
participation, interfere with safety assessments, or interfere with interpretation of 
results. 
7. The participant has a history of diagnosis or condition that, in the judgment of the 
investigator, may affect study endpoint assessment or compromise participant safety, 
specifically the following: 
a) Congenital or acquired immunodeficiency 
b) Chronic hepatitis or suspected active hepatitis 
c) A bleeding disorder that is considered a contraindication to intramuscular (IM) 
injection or phlebotomy, or non-receipt of vitamin K at birth  
d) Dermatologic conditions that could affect local solicited adverse reaction (AR) 
assessments 

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e) Any prior diagnosis of malignancy  
f) Febrile seizures 
8. The participant has received the following: 
a) Any routine vaccination with inactivated or live vaccine(s) within 14 days prior 
to first or second vaccination or plans to receive such a vaccine within 14 days 
of any study vaccination. 
b) Systemic immunosuppressants or immune-modifying drugs (including maternal 
use during pregnancy or lactation) for > 14 days in total within 6 months prior 
to the day of enrollment (for corticosteroids, ≥ 1 mg/kg/day or, if participant 
weighs > 10 kg: ≥ 10 mg/day prednisone equivalent). 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. 
c) Intravenous or subcutaneous blood products (red blood cells, platelets, 
immunoglobulins) within 3 months prior to enrollment. 
9. The participant has participated in an interventional clinical study within 28 days prior 
to the Screening Visit or plans to do so while participating in this study, or maternal 
participation in an interventional clinical study during pregnancy. 
10. The participant is an immediate family member, or household contact, of an employee 
of the study site or Sponsor or someone otherwise directly involved with the conduct 
of the study. As applicable, family members/household contacts of employees of the 
larger institution or affiliated private practice not part of the study site may be enrolled. 
11. The participant is a child who has been placed under the control or protection of an 
agency, organization, institution or entity by the courts, the government, or a 
government body, acting in accordance with powers conferred on them by laws and 
regulation. Does not include a child who is adopted or has an appointed legal guardian. 
Study Treatment 
Study Intervention Dose/Route/Schedule 
The mRNA-1273.214 IP contains CX-024414, the mRNA that encodes for the prefusion 
stabilized spike glycoprotein (S-2P) of the Wuhan-Hu-1 isolate of SARS-CoV-2 and 
CX-031302, the mRNA that encodes for the S-2P of the SARS-CoV-2 B.1.1.529 variant. 

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The IP will be administered as an IM injection into the anterolateral thigh. In Part 1, this will 
be a 5 µg or 10 µg dose level on a 2-dose schedule on Days 1 and 57, while in Part 2, the 
chosen dose from Part 1 will be administered on a 2-dose schedule on Days 1 and 57. 
Placebo (as applicable) Route/Schedule 
Placebo (0.9% sodium chloride) IM injection. 
Study Assessments and Procedures 
Immunogenicity Assessments: 
The following analytes will be measured in blood samples for immunogenicity assessments 
and biomarker samples: 
• Serum neutralizing antibody (nAb) titer against SARS-CoV-2 as measured by 
pseudovirus and/or live virus neutralization assays, including variants of concern 
(VOC; Omicron). 
• Serum binding antibody (bAb) titer as measured by a multiplex ligand-binding assay 
specific to the SARS-CoV-2 S protein. 
• Serum bAb titer as measured by a multiplex ligand-binding assay specific to the 
SARS-CoV-2 nucleocapsid protein. 
• Testing for serologic markers for SARS‑CoV‑2 infection as measured by 
anti‑nucleocapsid antibodies detected by immunoassay. 
Effectiveness Assessments: 
In this study, vaccine effectiveness for infants 12 weeks to < 6 months of age will be inferred 
based on serum antibody (Ab) responses obtained on Day 85 (28 days after the second 
injection of mRNA-1273.214 primary series) as compared against serum Ab responses 
obtained in adult participants at Day 57 in Study mRNA-1273-P301, based on geometric mean 
titer (GMT) and seroresponse. 
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). Solicited ARs will be recorded daily 
using electronic diaries. 

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• Unsolicited adverse events (AEs) observed or reported during the 28 days following 
each injection (ie, the day of injection and 27 subsequent days). 
• AEs leading to discontinuation from Day 1 through end of study (EoS). 
• Medically attended AEs (MAAEs) from Day 1 through EoS. 
• Serious AEs (SAEs) from Day 1 through EoS. 
• AEs of special interest (AESIs) from Day 1 through EoS. 
• Assessments for SARS-CoV-2 infection from Day 1 through EoS. 
Safety Oversight 
The contract research organization’s medical monitor, the Sponsor’s medical monitor, and the 
individual study site investigators will monitor safety throughout the study. 
Internal Safety Team: 
An IST will review safety data throughout the study and provide a recommendation to further 
dose participants. In addition, the IST will escalate any safety concerns to the data safety 
monitoring board (DSMB). The frequency of IST meetings will be described in more detail in 
the IST charter. 
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 study 
conduct and free of conflict of interest. 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. 
Cardiac Event Adjudication Committee: 
An independent cardiac event adjudication committee (CEAC) that includes pediatric 
cardiologists will review suspected cases of myocarditis and/or pericarditis to determine if 
they meet CDC criteria of “probable” or “confirmed” events, assess severity, and make 
recommendations in consultation with the DSMB, if necessary, to the Sponsor. The CEAC 
will operate under the rules of an approved charter. Details regarding the CEAC composition, 
responsibilities, procedures, and frequency of data review will be defined in its charter. 

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Statistical Analysis Plan 
Hypothesis Testing: 
Part 1: 
There is no statistical hypothesis to be tested in Part 1. 
Part 2: 
Primary Hypotheses: 
1) HA1: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months 
is noninferior to the primary series of 100 µg mRNA-1273 in adults based on 
geometric mean titer ratio (GMR) against the VOC (Omicron) with a noninferiority 
margin of 1.5-fold (lower bound of confidence interval [CI] for GMR > 0.67). 
2) HA2: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months 
is noninferior to the primary series of 100 µg mRNA-1273 in adults based on 
difference in seroresponse rate (SRR) against the VOC (Omicron) with a noninferiority 
margin of < 5% (lower bound of CI for SRR > –5%). 
Secondary Hypotheses: 
3) HA3: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months 
is superior to the primary series of 100 µg mRNA-1273 in adults based on GMR 
against the VOC (Omicron) with a superiority margin of > 1-fold (lower bound of CI 
for GMR > 1). 
4) HA4: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months 
is superior to the primary series of 100 µg mRNA-1273 in adults based on difference in 
SRR against the VOC (Omicron) with a superiority margin of > 0% (lower bound of 
CI for SRR > 0%). 
5) HA5: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months 
is “super” superior to the primary series of 100 µg mRNA-1273 in adults based on 
GMR against the VOC (Omicron) with a “super” superiority margin of > 1.5-fold 
(lower bound of CI for GMR > 1.5). 
6) HA6: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months 
is “super” superior to the primary series of 100 µg mRNA-1273 in adults based on 
difference in SRR against the VOC (Omicron) with a “super” superiority margin of 
> 10% (lower bound of CI for SRR > 10%). 

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7) HA7: The immune response of mRNA-1273.214 against the VOC (Omicron) in 
participants 12 weeks to < 6 months is noninferior to the primary series of 100 µg 
mRNA-1273 against the SARS-CoV-2 original strain in adults, based on GMR with a 
noninferiority margin of 1.5-fold (lower bound of CI for GMR > 0.67). 
8) HA8: The immune response of mRNA-1273.214 against the VOC (Omicron) in 
participants 12 weeks to < 6 months is noninferior to the primary series of 100 µg 
mRNA-1273 against the SARS-CoV-2 original strain in adults, based on difference in 
SRR with a noninferiority margin of < 5% (lower bound of CI for SRR > –5%). 
9) HA9: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months 
is noninferior to the primary series of 100 µg mRNA-1273 in adults based on GMR 
against the SARS-CoV-2 original strain with a noninferiority margin of 1.5-fold (lower 
bound of CI for GMR > 0.67). 
10)  HA10: The immune response of mRNA-1273.214 in participants 12 weeks to 
< 6 months is noninferior to the primary series of 100 µg mRNA-1273 against the 
original strain in adults based on difference in SRR against the SARS-CoV-2 original 
strain with a noninferiority margin of < 5% (lower bound of CI for SRR > –5%). 
Sample Size and Power Calculation: 
In Part 2, approximately 600 infant participants of 12 weeks to < 6 months age will be enrolled 
at the dose level selected for Part 2, with an mRNA-1273.214 to placebo ratio of 1:1. 
Assuming 10% to 15% participants are not negative SARS-CoV-2 status at baseline, it is 
estimated that there will be a minimum of approximately 250 evaluable participants in the 
mRNA-1273.214 arm eligible for immunogenicity analyses.  
The sample size of approximately 300 infant participants in the mRNA-1273.214 arm in Part 2 
is considered to be sufficient to support a safety assessment. There is at least 90% probability 
to observe at least 1 participant with an AE at a true AE rate of 1% in this group.  
The sample size calculation for each of the 2 primary noninferiority hypothesis tests (HA1 and 
HA2) was performed, and the larger sample size was chosen for the study. 
• With approximately 250 evaluable participants receiving mRNA-1273.214 in the Per-
Protocol Immunogenicity Set - SARS-CoV-2 Negative (PPIS-Neg) in Study mRNA-
1273-P206 and adults (≥ 18 years of age) in Study mRNA-1273-P301, there will be at 
least 90% power to demonstrate noninferiority of the immune response against 
Omicron variant, as measured by the GMT, in infant population at a 2‑sided alpha of 
0.05, compared with that in adults (≥ 18 years of age) in Study mRNA-1273-P301 
receiving mRNA‑1273, assuming an underlying GMR (which is calculated as ratio of 

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GMT) value of 1 and the standard deviation of the natural log-transformed titer is 
assumed to be 1.0, and a noninferiority margin of > 0.67. 
• With approximately 250 evaluable participants receiving mRNA-1273.214 in the 
PPIS-Neg in Study mRNA-1273-P206 and adults (≥ 18 years of age) in 
Study mRNA-1273-P301, there will be at least 90% power to demonstrate 
noninferiority of the immune response against Omicron variant as measured by SRR in 
infants at a 2-sided alpha of 0.05, compared with SRR against Omicron variant in 
adults ≥ 18 years of age in Study mRNA-1273-P301 receiving mRNA-1273, assuming 
SRR of 60% to 70% in Study mRNA-1273-P301, true SRR improvement of 10% in 
infants from Study mRNA-1273-P206 compared with adults from Study mRNA-
1273-P301, and a noninferiority margin of 5%.  
Analysis Populations: 
Analysis Set 
Description 
Randomization Set 
All participants who are randomly assigned in Part 2, regardless of the 
participants’ treatment status in the study. 
FAS 
Part 1: All enrolled participants in Part 1 who receive at least 1 dose of 
mRNA-1273.214. 
Part 2: All randomized participants in Part 2 who receive at least 1 dose 
of IP. 
mITT Set 
All participants in the FAS who have no serologic or virologic 
evidence of prior SARS-CoV-2 infection at baseline (ie, both negative 
RT-PCR test for SARS-CoV-2 and negative serology test based on 
bAb specific to SARS-CoV-2 nucleocapsid). 
mITT-1 Set 
All participants in the mITT Set excluding those who received wrong 
treatment (ie, at least 1 dose received that is not as randomized).  
PP Set 
All participants in the FAS who receive planned doses of IP per 
schedule and are SARS-CoV-2 negative at baseline (ie, both negative 
RT-PCR test for SARS-CoV-2 and negative serology test) and have no 
major protocol deviations that impact key or critical data. 
Immunogenicity Set 
All participants in the FAS who provide immunogenicity samples. 
PPIS 
Participants in the Immunogenicity Set who receive planned doses of 
IP per schedule, comply with immunogenicity testing schedule, and 
have no major protocol deviations that impact key or critical data. The 
PPIS will be used for analyses of immunogenicity. 
PPIS-Neg 
Participants in the PPIS who have no serologic or virologic evidence of 
SARS-CoV-2 infection at baseline (ie, both negative RT-PCR test for 
SARS-CoV-2 and negative serology test). The PPIS-Neg will be the 
primary analysis set for analyses of immunogenicity. 

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Safety Set 
All enrolled participants in Part 1 and all randomly assigned 
participants in Part 2 who receive at least 1 dose of IP. The Safety Set 
will be used for all analyses of safety except for solicited ARs.  
Solicited Safety Set 
All participants in the Safety Set who contribute any solicited AR data. 
The Solicited Safety Set will be used for the analyses of solicited ARs.  
Abbreviations: AR = adverse reaction; bAb = binding antibody; FAS = Full Analysis Set; IP = investigational 
product; mITT = modified intent-to-treat; mRNA = messenger RNA; PP = per protocol; PPIS = Per-Protocol 
Immunogenicity Set; PPIS-Neg = Per-Protocol Immunogenicity Set – SARS-CoV-2 Negative; RT-PCR = reverse 
transcriptase polymerase chain reaction; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2. 
Statistical Analyses 
Immunogenicity Analyses: 
The primary analysis population for immunogenicity will be the PPIS-Neg, unless specified 
otherwise. The primary objective of Part 2 of this study is to use the immunogenicity response 
to infer effectiveness of mRNA-1273.214 vaccine administered as 2 doses 8 weeks apart in 
infants aged 12 weeks to < 6 months at the dose level selected for investigation.  
Immunogenicity Analyses for mRNA-1273.214 Primary Series: 
Immune response as measured by GMT value and SRR in the infant group based on Ab levels 
will be compared to that in adult (≥ 18 years of age) participants from 
Study mRNA-1273-P301 using Ab data. The immunogenicity data from participants who are 
assigned to the same dose level in Part 1 and Part 2 of this study may be combined for the 
immunogenicity analyses. 
To assess the difference in immune response between the infant participants in 
Study mRNA-1273-P206 at 28 days after the last dose of mRNA-1273 primary series 
compared to the adult (≥ 18 years of age) participants in Study mRNA-1273-P301 at Day 57, 
an analysis of covariance model will be carried out with Ab as dependent variable and a group 
variable (an mRNA-1273 arm/group of Study mRNA-1273-P206 versus participants in 
Study mRNA-1273-P301) as the fixed variable for each participant arm/group, the analysis 
may adjust for key characteristics such as age, sex, etc. The GMT value of mRNA-1273.214 
arm at 28 days after the last dose of mRNA-1273.214 primary series and GMT value of 
mRNA-1273 at Day 57 (28 days after the second dose of primary series) in Study 
mRNA-1273-P301 will be estimated by the geometric least square mean (GLSM) from the 
model. The GMR (which is calculated as ratio of GMT) will be estimated by the ratio of 
GLSM from the model. The corresponding 2-sided 95% CI of GMR will also be provided.  
 

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The noninferiority of GMT of mRNA-1273.214 primary series compared with mRNA-1273 
primary series will be considered demonstrated if: 
• The lower bound of the 95% CI of the GMR (the infant participants in 
Study mRNA-1273-P206 at 28 days after the last dose of mRNA-1273.214 primary 
series, compared with the participants in Study mRNA-1273-P301 at Day 57) > 0.67 
based on the noninferiority margin of 1.5.  
In addition, the GMT of antibodies with corresponding 95% CI will be provided at each time 
point. The 95% CIs will be calculated based on the t-distribution of the log-transformed titer 
values then back transformed to the original scale. Descriptive summary statistics for GMT 
including median, minimum, and maximum will also be provided. 
The geometric mean fold rise of specific antibodies with corresponding 95% CI at each post-
baseline time point over pre-Dose 1 baseline at Day 1 will be provided. The 95% CIs will be 
calculated based on the t-distribution of the log-transformed values then back transformed to 
the original scale for presentation.  
The number and percentage of participants with seroresponse due to vaccination will be 
provided with 2-sided 95% CI using the Clopper-Pearson method at each post-baseline time 
point with Day 28 after the last dose of mRNA-1273.214 primary series being of the primary 
interest in the analyses, where seroresponse is defined as a titer 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 SRR difference with 95% CI (using Miettinen-Nurminen score method) between infants 
receiving mRNA-1273.214 primary series in Study mRNA-1273-P206 at 28 days after the last 
dose of mRNA-1273.214 primary series and adult participants receiving mRNA-1273 primary 
series in Study mRNA-1273-P301 at Day 57 will be provided.  
The noninferiority of seroresponse of mRNA-1273.214 primary series in Study 
mRNA-1273-P206 compared with mRNA-1273 primary series in Study mRNA-1273-P301 
will be considered demonstrated if: 
• The lower bound of the 95% CI of the SRR difference is > –5% based on the 
noninferiority margin of 5%. 

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Hypothesis Testing Strategy for Immunogenicity: 
The hypothesis tests for noninferiority, superiority, and “super” superiority of 
mRNA-1273.214 against Omicron as compared to mRNA-1273 primary series against 
Omicron will be performed sequentially. The noninferiority hypotheses (hypotheses HA1 and 
HA2) will be tested first. 
Once noninferiority is demonstrated based on both GMT and SRR, superiority (hypotheses 
HA3 and HA4) of mRNA-1273.214 as compared to mRNA-1273 primary series will be tested. If 
the lower bound of the 95% CI of the GMR is > 1, superiority based on GMT is demonstrated; 
if the lower bound of the 95% CI of the SRR difference is > 0%, superiority based on 
seroresponse is demonstrated. 
Once superiority is demonstrated based on both GMT and SRR, “super” superiority 
(hypotheses HA5 and HA6) of mRNA-1273.214 as compared to mRNA-1273 primary series 
will be tested. If the lower bound of the 95% CI of the GMR is > 1.5, “super” superiority 
based on GMT is demonstrated; if the lower bound of the 95% CI of the SRR difference is 
> 10%, “super” superiority based on seroresponse is demonstrated. 
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 vaccination 
group (dose levels of mRNA-1273.214 and placebo).  
Safety and reactogenicity will be assessed by clinical review of all relevant parameters 
including solicited ARs (local and systemic events), unsolicited AEs, SAEs, MAAEs, AESIs, 
and AEs leading to discontinuation from IP and/or study participation.  
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 
by toxicity grade 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, severe AEs, 
and AEs leading to discontinuation from IP or withdrawal from the study will be summarized. 
Unsolicited AEs will be presented by Medical Dictionary for Regulatory Activities preferred 
term and system organ class. 
Solicited AR events (starting within 7 days after any injection) that are serious or lasting 
beyond Day 7 after any injection will also be reported as unsolicited AEs. 

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The number of events of solicited ARs, unsolicited AEs/SAEs, MAAEs, severe AEs, and AEs 
leading to discontinuation from IP or withdrawal from the study will be reported in summary 
tables accordingly. 
For all other safety parameters, descriptive summary statistics will be provided in the 
statistical analysis plan (SAP). 
Subgroup Analyses: 
Subgroup analyses will be performed in select subgroups including but not limited to the 
following subgroups: 
• Sex (male, female) 
• SARS-CoV-2 status at baseline  
• Maternal immunization status  
• Race 
• Ethnicity 
Details of subgroups analyses will be provided in the SAP. 
Planned Analyses: 
Interim Analyses 
For Part 1, interim analyses of safety and immunogenicity will be performed after all treated 
participants in one or both arms have completed 28 days after the last dose of the primary 
series of mRNA-1273.214.  
For Part 2, an interim analysis of safety and immunogenicity will be performed after all 
participants have completed 28 days after the last dose of the primary series of 
mRNA-1273.214. This interim analysis will be considered the primary analysis for 
immunogenicity.  
Final Analyses 
The final analysis of all endpoints will be performed after participants have completed all 
planned study procedures. Results of this analysis will be presented in a final clinical study 
report, including individual listings. 
Additional information about all study analyses may be provided in the SAP. 
 
 
 

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1.2. 
Study Schema 
The study schema is presented in Figure 1. 
Figure 1: Study Schema 
 
Abbreviations: D = Day; EOS = end of study; IST = internal safety team; mRNA = messenger RNA; N = number of 
participants. 
a. Participant must be 12 weeks old at Day 1.  
b. Arm 2 will begin enrollment after IST review of safety data collected from 25 participants in Arm 1 who have 
reached Day 64 (1 week after second dose of 5 µg). 
c. At selected dose level from Part 1.  
 

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1.3. 
Schedule of Assessments 
Table 1: Schedule of Assessments (Part 1 and Part 2) 
Visit Number 
0 
1 
2 
3 
 
4 
5 
6 
7 
 
8 
 
9 
USV 
Type of Visit 
C 
C 
C 
TM SFU 
C 
C 
TM 
C 
SFU 
C 
SFU 
C 
C 
Month Time Point 
 
M0 
M0 
 
SC 
M2 
M2 
 
M3 
eDiary 
SC 
M8 
eDiary 
SC 
M14 
Up to 
M14 
Study Visit Day 
D-28 to D1 
(Screening)1 
D1 (Baseline) 
D42 
D8 
D293 
D574 
D602 
D644 
D854, 5 
Every 4 weeks  
D99 – D2114, 6 
Every 4 weeks  
D113– D2253, 4 
D237 
Every 8 weeks  
D265– D3774, 6 
Every 8 weeks  
D293– D4053, 4 
D422 
365 days after D573, 4 
Unscheduled Visit7, 8 
Window Allowance (Days) 
– 
– 
±1 
+ 3 
 
–14/+ 7 
±1 
+ 3 
–14/+ 7 
± 7 
± 7 
± 14 
± 7 
± 7 
± 14 
N/A 
Days Since Most Recent 
Injection 
– 
0 
3 
7 
28 
57 
3 
7 
28 
– 
– 
180 
– 
– 
365 
 
ICF, demographics, concomitant 
medications, medical history9  
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Review of inclusion and exclusion 
criteria 
X 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Physical examination and vital 
signs including length/height, 
weight and body temperature10 
X 
X 
X 
 
 
X 
X 
 
X 
 
 
X 
 
 
X 
X 
Randomization  
 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Study injection11 
 
X 
 
 
 
X 
 
 
 
 
 
 
 
 
 
 
Blood sample for vaccine 
immunogenicity12 
 
X 
 
 
 
 
 
 
X 
 
 
X 
 
 
X7 
 
Blood sample for SARS-CoV-2 
surveillance13 
 
X 
 
 
 
 
 
 
X 
 
 
 
 
 
 
 
Nasal swab sample for 
SARS-CoV-213 
 
X 
 
 
 
X 
 
 
X 
 
 
X 
 
 
X 
X 

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Visit Number 
0 
1 
2 
3 
 
4 
5 
6 
7 
 
8 
 
9 
USV 
Type of Visit 
C 
C 
C 
TM SFU 
C 
C 
TM 
C 
SFU 
C 
SFU 
C 
C 
Month Time Point 
 
M0 
M0 
 
SC 
M2 
M2 
 
M3 
eDiary 
SC 
M8 
eDiary 
SC 
M14 
Up to 
M14 
Study Visit Day 
D-28 to D1 
(Screening)1 
D1 (Baseline) 
D42 
D8 
D293 
D574 
D602 
D644 
D854, 5 
Every 4 weeks  
D99 – D2114, 6 
Every 4 weeks  
D113– D2253, 4 
D237 
Every 8 weeks  
D265– D3774, 6 
Every 8 weeks  
D293– D4053, 4 
D422 
365 days after D573, 4 
Unscheduled Visit7, 8 
Window Allowance (Days) 
– 
– 
±1 
+ 3 
 
–14/+ 7 
±1 
+ 3 
–14/+ 7 
± 7 
± 7 
± 14 
± 7 
± 7 
± 14 
N/A 
Days Since Most Recent 
Injection 
– 
0 
3 
7 
28 
57 
3 
7 
28 
– 
– 
180 
– 
– 
365 
 
Surveillance for 
COVID-19/illness visit7 
 
 
 
 
X 
X 
X 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
eDiary activation for recording 
solicited ARs (7 days)8 
 
X 
 
 
 
X 
 
 
 
 
 
 
 
 
 
 
Review of eDiary data 
 
 
X 
X 
 
 
X 
X 
 
 
 
 
 
 
 
 
Follow-up safety telephone calls14 
 
 
 
 
X 
 
 
 
 
 
X 
 
 
X 
 
 
Recording of unsolicited AEs 
 
X 
X 
X 
X 
X 
X 
X 
X 
 
 
 
 
 
 
 
Recording of MAAEs, SAEs, and 
AESIs and concomitant 
medications and procedures 
relevant to or for the treatment of 
the MAAE and SAE15 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Recording of concomitant 
medications and procedures and 
nonstudy vaccinations16 
 
X 
X 
X 
X 
X 
X 
X 
X 
 
X 
X 
 
X 
X 
X 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; C = clinic visit; COVID-19 = coronavirus disease 2019; 
D = day; eCRF = electronic case report form; EDC = electronic data capture; eDiary = electronic diary; FDA = Food and Drug Administration; ICF = informed 
consent form; IRB = institutional review board; LAR = legally acceptable representative; M = month; MAAE = medically attended adverse event; N/A = not 
applicable; RT-PCR = reverse transcriptase polymerase chain reaction; SAE = serious adverse event; SARS-CoV-2 = severe acute respiratory syndrome 
coronavirus 2; SC = safety (telephone) call; SFU = safety follow-up; TM = telemedicine visit or call; USV= unscheduled visit. 

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Note: In accordance with FDA Guidance on Conduct of Clinical Trials of Medical Products During COVID-19 Public Health Emergency (FDA March 2020), 
investigators may convert study site visits to home visits or telemedicine visits (with the exception of Screening, Day 1, Day 57, Day 85, Day 237, and Day 422) 
with the approval of the Sponsor (home visits also require site IRB approval). 
1. 
Screening Visit and Day 1 may be combined on the same day. Additionally, the Screening Visit may be performed over multiple visits if performed within 
the 28-day screening window. 
2. 
Day 4 and Day 60 clinic visits will only be performed in Part 1 of study. 
3. 
Safety follow-up via a safety telephone call will be performed on Day 29, every 4 weeks from Day 113 to Day 225, and every 8 weeks from Day 293 to 
Day 405. 
4. 
If the visit for the second dose (Day 57) is disrupted and cannot be completed at Day 57 (–14/+7 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 57 + 14 days. When the extended visit window is used, the remaining study visits should be rescheduled 
to follow the intervisit interval from the actual date of the second dose.  
5. 
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 remote evaluation via a telemedicine visit or call should be conducted in place of the study site visit (except for dosing 
visits and visits that require a blood draw). The remote evaluation 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, 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’s parent(s)/LAR(s) via informed consent and have prior approval from the Sponsor (or its designee). 
6. 
Safety follow-up via an eDiary questionnaire will be performed every 4 weeks from Day 99 to Day 211 and every 8 weeks from Day 265 to Day 377. 
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 
pre-specified criteria of suspicion for COVID-19, the participant 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 to evaluate for the presence of SARS-CoV-2 infection) 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. 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. 
At each injection visit, participants’ parent(s)/LAR(s) will record data into the eDiary starting approximately 30 minutes after injection under the 
supervision of the study site staff to ensure successful entry of assessment. Participants’ parent(s)/LAR(s) will continue to record entries 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. Capturing 
details of ARs in the eDiary should not exceed 7 days after each vaccination. If a solicited local or systemic AR continues beyond Day 7 after vaccination, 
the event should be reviewed by the study site staff either via a telephone call or at an unscheduled study site visit. 
9. 
Verbal medical history is acceptable. 
10. 
A full physical examination and vital signs assessments, including length/height, weight, and body temperature, will be performed at the Screening Visit 
(and on Day 1, if Day 1 and Screening Visit occur on separate days). Symptom-directed physical examinations and vital signs assessments will be 
performed on Day 1, Day 4 (in Part 1), Day 57, Day 60 (in Part 1), Day 85, Day 237, Day 422, and USV, and may be performed at other time points at the 
discretion of the investigator. Body temperature should be measured on each injection day prior to injection. Body temperature must be measured via the 
axillary route and any axillary reading of ≥ 37.8°C/≥ 100°F may be confirmed by a rectal measurement. On each injection day before injection and again 7 
days after injection, the injection site should be examined. Any clinically significant finding identified during a study visit should be reported as an MAAE. 

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Participants who are febrile (≥ 38.0°C/≥ 100.4°F) before injection on Day 1 or Day 57 must have the visit rescheduled within the relevant visit window to 
receive the injection. Afebrile participants with minor illnesses may be injected at the discretion of the investigator. 
11. 
Study injection postdose observation will be 60 minutes for Part 1 and 30 minutes for Part 2.  
12. 
On Day 1, sample must be collected prior to randomization and dosing. If a Day 1 (baseline) blood sample cannot be obtained, the participant could be 
rescheduled within the allowable screening period one time. If a blood sample still cannot be obtained at the rescheduled visit, then the participant will be 
considered a screen failure due to inability to satisfy inclusion criterion 3. 
13. 
The nasal swab and blood sample (collected before dosing on each injection day and on other scheduled days per the SoA) will be used to ascertain the 
presence or history of SARS-CoV-2 infection via RT-PCR and serum binding antibody specific to SARS-CoV-2 nucleocapsid, respectively. 
14. 
Medically qualified and trained study site personnel will call all participants to collect information relating to any MAAEs, SAEs, AEs leading to study 
withdrawal and 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 any COVID-19 symptoms the 
participant may experience. 
15. 
A list of AESIs pertinent to this study is maintained by the Sponsor and provided to each investigator. All SAEs and AESIs will 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 
SAE or AESI from a study participant or receives updated data on a previously reported SAE or AESI and the eCRF has been taken offline, then the site 
can report this information on a paper SAE or AESI form using the SAE Mailbox, the SAE Hotline, or the SAE Fax line. 
16. 
All concomitant medications and procedures will be recorded through 28 days after each injection (through the completion of the Day 85 visit). All 
nonstudy vaccines given at any time during the study period should be recorded. All concomitant medications relevant to or for the treatment of an SAE, 
MAAE, or AESI will be recorded from Day 1 through the final visit (Day 422). 
 
 

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2. 
INTRODUCTION 
2.1. 
Study Rationale 
There is currently no approved vaccine against SARS‑CoV‑2 for young infants. Although 
another mRNA vaccine is available to older children under EUA, the youngest pediatric 
population remains unprotected because the duration of protection conferred on infants by 
transplacentally transferred antibodies is not currently known (Halasa et al 2022). In addition, 
due to the shift in the disease burden to younger children over the course of the COVID-19 
pandemic, there is an urgent need for pediatric vaccination strategies that induce broader 
protection against SARS-CoV-2 VOC, including the Omicron variant, to decrease childhood 
morbidity and mortality. Based on the experience of mRNA-1273 in adults and leveraging the 
flexible nature of the mRNA technology, ModernaTX, Inc (the Sponsor) is evaluating mRNA 
vaccines to address the Omicron variant in infants. 
2.2. 
Background and Overview 
Coronaviruses are a large family of viruses that cause illness ranging from the common cold to 
more severe diseases, such as MERS and SARS. An outbreak of a novel coronavirus (later 
designated SARS-CoV-2) initially emerged in Wuhan, Hubei Province, China in December 
2019, then spread internationally. The WHO declared COVID-19 a Public Health Emergency of 
International Concern (its highest category of public health threat) on 30 Jan 2020 
(WHO 2020a), and as a global pandemic on 11 Mar 2020 (WHO 2020b). As of 15 Apr 2022, 
confirmed COVID-19 mortality surpassed 6.1 million worldwide and over 988,000 in the US, 
with COVID-19 cases numbered nearly 502.9 million worldwide and over 80 million in the US 
(Dong et al 2020).  
Since the beginning of the COVID-19 pandemic, cases of severe disease and deaths associated 
with COVID-19 have occurred more frequently in adults (Hay et al 2020; Ayoub et al 2020; 
CDC 2022b); however, COVID-19 can also lead to severe outcomes in children (Kim et al 2020; 
Havers et al 2021). By March 2022, over 7.7 million cases of COVID-19 had been reported 
among ages 0 to 4 years in 104 countries (UNICEF 2022). In the US, there have been over 
2.2 million cases of COVID-19 and over 465 deaths due to COVID-19 reported among children 
0 to 4 years of age (CDC 2022a), and an excess of 3578 hospitalizations among children 0 to 
4 years of age have been observed in the COVID-19-Associated Hospitalization Surveillance 
Network (COVID-NET) system through 09 Apr 2022 due to COVID-19, with 24.1% requiring 
ICU interventions and more than 21 related in-hospital deaths (CDC 2022b).  
Of particular concern is the phenomenon known as MIS-C, a hyperinflammatory syndrome with 
features of Kawasaki disease in children and adolescents infected with SARS-CoV-2 

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(PICS 2020; Belhadjer et al 2020; Dufort et al 2020; Verdoni et al 2020). The condition affects a 
variety of organ systems, including the gastrointestinal, cardiovascular, hematologic, 
mucocutaneous, and respiratory systems. Through 28 Mar 2022, there were a total of 7880 cases 
of MIS-C reported in the US with approximately 3.2% reported among the less than 1-year-old 
age group and 20.8% reported among the 1- to 4 year-old age group (CDC 2022c).  
Over the course of the pandemic, SARS-CoV-2 variants have emerged and have raised concern, 
due to reports of increased infectivity or reduction in the neutralization ability of convalescent 
sera or sera from vaccinated participants (Pajon et al 2022). The emergence of these variants 
indicates that SARS-CoV-2 evolution may lead to immune escape and allow the pathogen to 
develop more efficient transmission between human hosts (Martin et al 2021). Hence, 
vaccination strategies to control the virus need to be responsive to this evolution. 
In November 2021, the SARS-CoV-2 Omicron variant (B.1.1.529) was detected in South Africa 
and was found to contain potential Ab 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. Clinical studies in adults conducted 
during the Omicron wave found lowered efficacy of the prototype vaccine against this new 
variant (Ferdinands et al 2022; Tseng et al 2022). Similar to the findings in adults in 
Study mRNA-1273-P204, which enrolled children under 12 years of age, efficacy of the 
mRNA-1273 vaccine was observed against symptomatic COVID-19 during the Omicron variant 
wave, but less than during previous variant waves (Tseng et al 2022). 
An evaluation of COVID-19 incidence over time indicates marked increases in the ages 0 to 
4 years with the Omicron variant wave. Prior to the Omicron wave, peak incidence among 0 to 
4 years was 187.0 incident cases per 100,000 population in August 2021, increasing to 
894.6 cases per 100,000 population during the Omicron wave in January 2022 (CDC 2022c).  
Data also suggests that the demographics of hospitalized patients with COVID-19 shifted to 
younger age groups after the onset of the Omicron wave (Goga et al 2021; UKHSA 2021; 
Abdullah et al 2022). The cumulative incidence of COVID-19-associated hospitalizations was 
49.7 per 100,000 children and adolescents from 01 Mar 2020 through 14 Aug 2021 
(Delahoy et al 2021). During the Omicron wave, hospitalizations among those aged 0 to 17 years 
rose to 46.2% when comparing the week of 01 to 07 Jan 2022 to the last week in 
December 2021. Children aged 0 to 4 years had a dramatic 5-fold increase in hospitalization 
from 2.9 to 15.6 per 100,000 children (Marks et al 2022). The proportion of emergency room 
visits diagnosed with COVID-19 increased from a peak of 4% prior to the Omicron wave to a 
peak of 13.8% among those 11 years and younger (CDC 2022d). These trends support the need 

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for pediatric vaccination strategies that induce broader protection against VOC in addition to the 
ancestral SARS-CoV-2 strain. To address this need, the Sponsor has developed mRNA-
1273.214, a bivalent vaccine which contains CX-024414, the mRNA that encodes for the 
prefusion stabilized spike glycoprotein (S-2P) of the Wuhan-Hu-1 isolate of SARS-CoV-2 and 
CX-031302, the mRNA that encodes for the S-2P of the SARS-CoV-2 B.1.1.529 variant. 
In December 2020, following review of safety and efficacy data observed to date, the FDA 
granted EUA to 2 mRNA-based SARS-CoV-2 vaccines, including mRNA-1273 for adults. In 
October 2021, the FDA granted EUA to an mRNA-based SARS-CoV-2 vaccine in children aged 
5 to 11 years old. To address prevention of pediatric COVID-19 as well as to potentially help 
curb SARS-CoV-2 transmission, there is an urgent public health need for rapid development of 
SARS-CoV-2 vaccines in children. Finally, there are currently no clinical trials evaluating the 
safety and effectiveness of COVID-19 vaccines in children under 6 months of age. 
Emerging evidence suggests that although maternal antibodies are transferred to infants 
transplacentally after maternal vaccination, titers wane over the course of the first 6 months of 
life and are undetectable in up to 43% of infants at 6 months of age, supporting the need for early 
vaccination in this age group (Shook et al 2022). While observational data (Halasa et al 2022) 
demonstrate that maternal vaccination during pregnancy can be 61% effective 
(95% CI = 31%-78%) in preventing hospitalization of infants aged < 6 months, there are no 
systematic studies of the need and risk-benefit of infant immunization against COVID-19. 
Additionally, it remains unknown if transferred passive immunity after maternal immunization 
with vaccines targeting prototype SARS-CoV-2 confer benefit of protection against emerging 
variants to the infants. Hence, there remains a need for active immunization strategies in this age 
group. 
In the ongoing Study mRNA-1273-P204 (data snapshot on 21 Feb 2022), the safety profile of the 
2 dose primary series in children and toddlers/infants (6 months to < 6 years of age) was 
generally consistent with the known safety profile observed in other studies of mRNA-1273. In 
addition, the events commonly seen in this pediatric population consisted primarily of grade 1 
and grade 2 reactogenicity occurring within 2 days after either dose lasting 2 to 3 days. Solicited 
local and systemic ARs in children 6 months to < 6 years of age were generally consistent with 
the AE profile of mRNA-1273 in older age groups with the exception of fever. Fever was most 
commonly reported on Day 1 or Day 2 after any vaccination and lasted for a median duration of 
1 day. Beyond Day 2 (after any dose) fever rates were similar between the mRNA-1273 group 
and the placebo group. Although no studies to date have evaluated mRNA-1273.214 in young 
children, ongoing trials in adults have not raised any safety concerns. Based on experience to 
date, the risk-benefit profile of evaluating mRNA-1273.214 in younger children is favorable.  

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The objective for this Phase 2 study is to evaluate the safety, tolerability, reactogenicity, and 
effectiveness of 2 dose levels (5 and 10 µg) of mRNA-1273.214 vaccine or another modified 
vaccine (both referred to as 1273.214 in the document) administered as 2 doses 8 weeks apart in 
participants aged 12 weeks to < 6 months. 
2.2.1. 
Nonclinical Studies 
mRNA-1273.214 was studied as a primary vaccination series in BALB/c mice. Mice were 
vaccinated with 2 doses of monovalent mRNA-1273, BA.1-matched monovalent 
mRNA-1273.529, or bivalent mRNA-1273.214, with the 2 doses administered 3 weeks apart. 
The mRNA-1273, mRNA-1273.529, and mRNA-1273.214 IPs administered are described in 
Section 6.1. 
At Day 36 (2 weeks after the second dose), robust serum nAb responses, determined via a 
research-grade vesicular stomatitis virus-based SARS-CoV-2 pseudovirus neutralization assay, 
were measured 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 mRNA-1273.529 had high neutralization Ab 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 affords 
broader neutralization across variants. 
Overall, these 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. 
Nonclinical study data for mRNA-1273 is available in the IB. 
2.2.2. 
Clinical Studies 
No finalized clinical study data is available for mRNA-1273.214. mRNA-1273.214 is being 
evaluated in the Sponsor’s trial, mRNA-1273-P205, a phase 2/3, open-label study to evaluate the 
immunogenicity and safety of mRNA vaccine boosters for SARS-CoV-2 variants, and 
mRNA-1273-P305, a phase 2/3, randomized, observer-blind, active-controlled study to evaluate 
the immunogenicity and safety of Omicron variant vaccines in comparison with mRNA-1273 
(prototype) booster vaccine. Preliminary data from the Sponsor’s Phase 2 trial 

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Study mRNA-1273-P205 suggest that mRNA-1273.211, a bivalent vaccine that contains mRNA 
encoding for the S-2P of Wuhan-Hu-1 and mRNA encoding for the S-2P of B.1.351 at a 
1:1 ratio, induced numerically similar or higher and more durable neutralizing responses against 
both vaccine matched and unmatched strains compared to the monovalent mRNA-1273 and 
mRNA-1273.351 (encodes for S-2P of B.1.351) vaccine. This supports the hypothesis that the 
bivalent mRNA-1273.214 vaccine to be tested in this study may generate more durable 
neutralizing responses against the Omicron variant strain and the prototype strain compared to 
mRNA-1273. 
Clinical study data for mRNA-1273, including in the pediatric age group, is available in the IB. 
2.3. 
Benefit/Risk Assessment 
2.3.1. 
Known Potential Benefits 
The following benefits may accrue to participants: 
• The mRNA-1273.214 vaccine may be an effective vaccine against COVID-19 in the 
study population, including diseases caused by VOC. 
• The mRNA-1273.214 vaccine may be effective in preventing the rare but serious 
complication of MIS-C (Zambrano et al 2022). 
• 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 bivalent vaccine against COVID-19 for 
participants aged 12 weeks to < 6 months. 
2.3.2. 
Risks From Study Participation and Their Mitigation 
The safety profile of mRNA-1273 is largely based on data from the pivotal Phase 3 study 
conducted in > 30,000 adults aged 18 years and older (Study mRNA-1273-P301). In addition, 
the safety of mRNA-1273 in > 10,000 children aged 6 months to < 6 years of age has been 
studied in Study mRNA-1273-P204. It is expected that the safety profile of mRNA‑1273.214 
will be similar to mRNA-1273. In the studies mRNA-1273-P205 and mRNA-1273-P305, 
443 (enrollment completed) and approximately 1250 (as of 24 May 2022) adults have received 
mRNA-1273.214, respectively. 
Intramuscular injection with other mRNA vaccines manufactured by the Sponsor containing the 
SM-102 LNP commonly results in a transient and self-limiting local inflammatory reaction. 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. Solicited ARs 

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were reported more frequently among vaccine participants than among placebo participants in 
both Study mRNA-1273-P301 and Study mRNA-1273-P204 (data cutoff 21 Feb 2022). 
In Study mRNA-1273-P301, the most frequently reported ARs after any dose in the vaccine 
group were pain at the injection site, fatigue, headache, myalgia, and chills. The most common 
solicited local AR was pain. Solicited systemic ARs were reported more frequently by vaccine 
participants after Dose 2 (fatigue [65.3%], headache [58.6%], myalgia [58%], and arthralgia 
[42.8%]) than after Dose 1 (fatigue [37.2%], headache [32.7%], myalgia [22.7%], and arthralgia 
[16.6%]). Grade 3 systemic ARs were also reported more frequently after Dose 2 than after 
Dose 1. The majority of local and systemic ARs had a median duration of 1 to 3 days. Several 
participants reported injection site reactions after Day 7 that were characterized by erythema, 
induration, and often pruritus. Consultation with a dermatopathologist suggested that these were 
most likely dermal hypersensitivity and were unlikely to represent a long-term safety concern. 
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 Study mRNA-1273-P204 (6 months to < 2 years), pain was the most commonly reported local 
solicited AR. In the infants, irritability/crying were the most commonly systemic solicited ARs, 
and in the older age group headache and fatigue were the most common systemic solicited ARs. 
Unsolicited AEs that occurred within 28 days following each vaccination were collected in both 
mRNA-1273-P301 and mRNA-1273-P204. In Study mRNA-1273-P301, these were reported by 
23.9% of participants who received mRNA-1273 and 21.6% of participants who received 
placebo. 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% vs. 0.6%). All of the lymphadenopathy events were similar to the axillary 
swelling/tenderness in the injected arm reported as solicited ARs. 
Hypersensitivity AEs in Study mRNA-1273-P301 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. 
In the placebo-controlled part of Study mRNA-1273-P204, overall incidence of unsolicited AEs 
was similar in participants who received mRNA-1273 and the placebo group (40% and 37.5%, 
respectively, in participants aged 2 to < 6 years of age; 49.3% and 48.2% in participants aged 
6 months to < 2 years, respectively). Unsolicited AEs that were higher in the mRNA-1273 group 

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compared with the placebo group by at least > 1% were as follows: in participants aged 2 years 
to < 6 years – injection site erythema (1.3% vs. 0.2%); and in participants aged 6 months to 
< 2 years – croup infections (1.3% vs. 0.3%), diarrhea (3.2% vs. 2.2%), and injection site 
lymphadenopathy (1.4% vs. 0.2%). Hypersensitivity AEs related to study vaccination were 
reported in 1.1% of vaccine recipients and 0.7% of placebo recipients in the 2- to < 6-year-old 
age group. In the 6 months to < 2-year age group, hypersensitivity AEs related to study 
vaccination were rare (< 0.1%). 
In Study mRNA-1273-P301 that included adults > 18 years of age, SAEs were reported at the 
same rates in participants who received mRNA-1273 and placebo from the first dose until the 
last observation. 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. 
There were no other notable patterns or numerical imbalances between study arms in 
Study mRNA-1273-P301 for specific categories of AEs (including other neurologic, 
neuro-inflammatory, and thrombotic events) that would suggest a causal relationship to 
mRNA-1273. 
During the placebo-controlled part of Study mRNA-1273-P204 (data cutoff 21 Feb 2022), there 
were no SAEs related to the study vaccination within 28 days of any dose in participants aged 2 
to < 6 years of age, while in participants aged 6 months to < 2 years, < 0.1% of participants in 
the treatment group experienced a related SAE (1 participant experienced an event of fever 
associated with a febrile seizure). No related SAEs were reported in the placebo group.  
In the post-authorization period, there have been very rare reports of anaphylaxis following 
mRNA-1273 administration. In addition, there have been very rare reports of myocarditis and 
pericarditis occurring after vaccination with COVID‑19 mRNA vaccines. The majority of the 
cases have been reported in male adolescents and young male adults 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. Investigators and study participants should be alert to 
the signs and symptoms of myocarditis and pericarditis (Gargano et al 2021). 
2.3.3. 
Overall Benefit/Risk Conclusion 
The proposed study is designed to evaluate the safety and immunogenicity of the 
mRNA-1273.214 vaccine for SARS‑CoV‑2 VOCs in participants aged 12 weeks to < 6 months 
administered as a 2-dose primary series. 

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Part 1 will enroll participants aged 12 weeks to < 6 months and assess 2 dose levels (5 and 
10 µg). Based on the safety and immunogenicity observed in Part 1, dose level for Part 2 will be 
selected. 
Part 2 will enroll participants aged 12 weeks to < 6 months in a placebo-controlled 
observer-blind evaluation of the selected dose level. 
Immunogenicity data from participants who receive the mRNA-1273.214 vaccine at the selected 
dose level will be used to infer vaccine effectiveness of the primary series. All participants will 
be followed up for 12 months after receipt of the second injection. 
Safety will be monitored throughout the study (Section 8.12). 
Although Phase 2/3 studies of mRNA-1273.214 are currently ongoing, the safety profile is 
expected to be similar to that of mRNA-1273 and other bivalent vaccines studied to date. Based 
on prior evidence of immunogenicity of bivalent vaccines (Chalkias et al 2022), 
mRNA-1273.214 may be used to address the current COVID‑19 outbreak as a result of its 
uniquely rapid and scalable manufacturing process. In particular, a safe and effective vaccine 
against SARS‑CoV‑2 and the Omicron VOC in young infants will help facilitate a return towards 
normalization of daily activities, including safe in-person attendance at childcare centers. 
Considering the lack of approved vaccines for SARS-CoV-2 and VOCs, the participants’ risk of 
COVID‑19 outside the study during a pandemic, the continued emergence of new variants, and 
the nonclinical and clinical data to date, the Sponsor considers the potential benefits of 
participation in this study to exceed the risks. 

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3. 
OBJECTIVES AND ENDPOINTS 
The objectives that will be evaluated in this study and endpoints associated with each objective 
are provided in Table 2 (Part 1) and Table 3 (Part 2). 
Table 2: Objectives and Endpoints for Part 1 
Objectives 
Endpoints 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety and 
reactogenicity of 2 dose levels1 of 
mRNA-1273.214 vaccine 
administered as 2 doses 8 weeks 
apart in participants aged 12 weeks 
to < 6 months 
• 
Solicited local and systemic ARs through 7 days after 
each injection 
• 
Unsolicited AEs through 28 days after each injection 
• 
MAAEs throughout the entire study period 
• 
SAEs throughout the entire study period 
• 
AESIs throughout the entire study period 
• 
AEs leading to discontinuation from study 
participation postdose throughout the entire study 
period 
Secondary Objectives 
Secondary Endpoints 
• 
To evaluate the immunogenicity of 
2 dose levels1 of mRNA-1273.214 
vaccine administered as 2 doses 
8 weeks apart in participants aged 
12 weeks to < 6 months 
• 
GMT of antibodies against SARS-CoV-2 VOC 
(Omicron) at 28 days after second dose 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; 
GMT = geometric mean titer; MAAE = medically attended adverse event; mRNA = messenger RNA; SAE = serious 
adverse event; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2; VOC = variants of concern. 
1. Dose levels of mRNA-1273.214 vaccine administered to participants will be 5 µg and 10 µg. 
 

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Table 3: Objectives and Endpoints for Part 2 
Objectives 
Endpoints 
Primary Objectives 
Primary Endpoints 
• 
To evaluate the safety and 
reactogenicity of selected dose level 
(from Part 1) of mRNA-1273.214 
vaccine administered as 2 doses 
8 weeks apart in participants aged 
12 weeks to < 6 months 
• 
Solicited local and systemic ARs through 7 days 
after each injection 
• 
Unsolicited AEs through 28 days after each 
injection 
• 
MAAEs throughout the entire study period 
• 
SAEs throughout the entire study period  
• 
AESIs throughout the entire study period 
• 
AEs leading to discontinuation from study 
participation postdose throughout the entire study 
period 
• 
To infer the effectiveness of 
selected dose level (from Part 1) of 
mRNA-1273.214 vaccine 
administered as 2 doses 8 weeks apart 
in participants aged 12 weeks to 
< 6 months 
• 
Co-primary Endpoint: GMT of antibodies against 
SARS-CoV-2 VOC (Omicron) at 28 days after the 
second dose of mRNA-1273.214 compared with that 
of the adult participants at Day 57 (28 days after the 
second dose) in Study mRNA-1273-P301 dosed 
with mRNA-1273 (100 µg, 2 doses 28 days apart) 
primary series 
• 
Co-primary Endpoint: SRR1 against SARS-CoV-2 
VOC (Omicron) at 28 days after the second dose of 
mRNA-1273.214 compared with that of the adult 
participants at Day 57 (28 days after the second 
dose) in Study mRNA-1273-P301 dosed with 
mRNA-1273 (100 µg, 2 doses 28 days apart) 
primary series 
Secondary Objectives 
Secondary Endpoints 
• 
To evaluate the immune response 
against SARS-CoV-2 VOC (Omicron) 
elicited by mRNA-1273.214 vaccine 
administered as 2 doses 8 weeks apart 
in participants aged 12 weeks to 
< 6 months, compared with the 
immune responses against original 
strain induced by mRNA-1273 
• 
GMT of antibodies and SRR against SARS-CoV-2 
VOC (Omicron) at 28 days after the second dose of 
mRNA-1273.214 primary series, compared with 
GMT and SRR against original strain at Day 57 
(28 days after the second dose) in 
Study mRNA-1273-P301 dosed with mRNA-1273 
primary series 

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primary series (100 µg, 2 doses 
28 days apart) 
• 
To evaluate the immune response 
against SARS-CoV-2 original strain 
elicited by mRNA-1273.214 vaccine 
administered as 2 doses 8 weeks apart 
in participants aged 12 weeks to 
< 6 months, compared with the 
immune responses against original 
strain induced by mRNA-1273 
primary series (100 µg, 2 doses 
28 days apart) 
• 
GMT of antibodies and SRR against SARS-CoV-2 
original strain at 28 days after the second dose of 
mRNA-1273.214 primary series, compared with 
GMT and SRR against original strain at Day 57 
(28 days after the second dose) in 
Study mRNA-1273-P301 dosed with mRNA-1273 
primary series 
Exploratory Objectives 
Exploratory Endpoints 
• 
To evaluate the incidence of 
COVID-19 after mRNA-1273.214 
vaccine administered as 2 doses 
8 weeks apart 
• 
The incidence of the first occurrence of COVID-19 
postbaseline, where COVID-19 is defined as 
symptomatic disease based on CDC case definition2  
• 
To evaluate the incidence of 
SARS-CoV-2 infection after 
mRNA-1273.214 vaccine administered 
as 2 doses 8 weeks apart 
• 
The incidence of SARS-CoV-2 infection including 
symptomatic and asymptomatic infection (by 
serology and/or RT-PCR) postbaseline 
SARS-CoV-2 infection will be defined in 
participants with negative SARS-CoV-2 at baseline:  
o bAb level against SARS-CoV-2 
nucleocapsid protein negative at Day 1, that 
becomes positive (as measured by ligand-
binding assay) postbaseline, OR 
o Positive RT-PCR postbaseline 
• 
To evaluate the incidence of 
asymptomatic SARS-CoV-2 infection 
after mRNA-1273.214 vaccine 
administered as 2 doses 8 weeks apart 
• 
The incidence of SARS-CoV-2 infection measured 
by RT-PCR and/or bAb levels against SARS-CoV-2 
nucleocapsid protein (by ligand-binding assay) 
postbaseline in participants with negative SARS-
CoV-2 at baseline, in the absence of any COVID-19 
symptoms 
• 
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)  

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Abbreviations: Ab = antibody; AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; 
bAb = binding antibody; CDC = Centers for Disease Control and Prevention; COVID-19 = coronavirus disease 
2019; GMFR = geometric mean fold rise; GMT = geometric mean titer; LLOQ = lower limit of quantification; 
MAAE = medically attended adverse event; mRNA = messenger RNA; RT-PCR = reverse transcriptase polymerase 
chain reaction; SAE = serious adverse event; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2; 
SRR = seroresponse rate; VOC = variants of concern. 
1. Seroresponse is defined as a titer change from baseline (pre-Dose 1) below the LLOQ to ≥ 4 × LLOQ, or at least a 
4-fold rise if baseline is ≥ LLOQ. 
2. The case definition of COVID-19 includes at least one of the following systemic symptoms: fever (temperature 
> 38ºC/≥ 100.4ºF) or chills (of any duration, including ≤ 48 hours); cough (of any duration, including ≤ 48 hours); 
shortness of breath or difficulty breathing (of any duration, including ≤ 48 hours); fatigue, headache, myalgia, 
nasal congestion or rhinorrhea, new loss of taste or smell, sore throat, abdominal pain, diarrhea, nausea or 
vomiting, poor appetite or poor feeding; AND a positive test for SARS-CoV-2 by RT-PCR. 
 
 
• 
To evaluate immune response elicited 
by the primary series of 
mRNA-1273.214 against variant(s) of 
interest 
• 
GMT, SRR, and GMFR of Ab against variant(s) of 
interest 

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4. 
STUDY DESIGN  
4.1. 
General Design 
This is a Phase 2, two-part, open-label in Part 1 and observer-blind, randomized, 
placebo-controlled in Part 2 study to evaluate the safety, tolerability, reactogenicity, and 
effectiveness of mRNA-1273.214 SARS-CoV-2 vaccine in infants aged 12 weeks to < 6 months. 
The study will be conducted at multiple sites in the US enrolling approximately 700 participants. 
Participants who withdraw or are withdrawn from the study will not be replaced. 
The study will be conducted in 2 parts. Part 1 will consist of Arm 1 and Arm 2 that will enroll 
sequentially, ie, Arm 1 will begin enrollment and the periodic safety review will determine 
whether Arm 2 can begin enrollment. A total of 100 participants (50 participants in each arm) 
will be enrolled in Part 1 and will receive 5 µg of mRNA-1273.214 in Arm 1 and 10 µg of 
mRNA-1273.214 in Arm 2. While participants may be screened up to 1 month prior to dosing, 
they must be 12 weeks completed age at the time of receipt of first dose. Arm 1 will start with 
2 doses of 5 µg (sentinel dosing) administered 8 weeks apart of up to 4 participants. An IST will 
review safety data after Dose 1 (1 week after Dose 1 of mRNA-1273.214) and provide a 
recommendation to further dose participants. Once safety and tolerability after Dose 1 have been 
reviewed by the IST, Arm 1 will continue enrollment for a total of 50 participants.  
The IST will reconvene once 25 participants in Arm 1 reach Day 64 (1 week after Dose 2 of 5 µg 
administered 8 weeks apart). If no safety concerns are identified after IST review in Arm 1, 
Arm 2 will begin enrollment and participants will receive 2 doses of 10 µg of mRNA-1273.214 
administered 8 weeks apart. Similar to Arm 1, safety and tolerability will be reviewed by the IST 
after 4 participants have received Dose 1 (1 week after Dose 1 of mRNA-1273.214), and again 
when 25 participants reach Day 64, and provide a recommendation for continuing dosing and 
enrollment at each review. Arm 2 will enroll a total of 50 participants. The immunogenicity and 
safety analysis will be conducted after all treated participants in both Arms 1 and 2 reach Day 85 
(28 days from second dose). The results from Part 1 will determine the dose level for Part 2, 
which will be blinded and randomized. 
Part 2 of the study will consist of 2 groups (Arm 3 and Arm 4). In Part 2, a total of 
approximately 600 participants will be randomly assigned to receive mRNA-1273.214 (Arm 3) 
or placebo (Arm 4) in a 1:1 ratio (n = 300 per arm). Part 2 will utilize the mRNA-1273.214 dose 
selected in Part 1. Study vaccine will be administered nonconcomitantly to routine pediatric 
vaccinations. Participants will be followed for approximately 12 months after completion of the 
primary series.  

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All participants will participate in a Screening Period, Treatment Period, and Follow-up Period. 
The study schema is illustrated in Figure 1 and the SoA is provided in Table 1. 
4.1.1. 
Study Periods 
This study involves up to 10 scheduled visits in Part 1 and 8 scheduled visits in Part 2. In both 
Part 1 and Part 2, there will be up to 6 in-person visits (if screening and baseline are done 
separately) and 2 remote visits (Visit 3 and Visit 6; remote evaluation by means of 
telecommunication technology or phone call). Two additional clinic visits on Day 4 and Day 60 
will be performed only in Part 1 (Table 1). 
The study duration for each participant will be approximately 15 months, which includes 1 month 
for screening (Day –28 to Day –1), 2 months for dosing (on Day 1 and Day 57), and 12 months of 
follow-up after the second dose. 
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 remote evaluation via a 
telemedicine visit or call should be conducted in place of the study site visit (except for dosing 
visits and visits that require a blood draw). The remote evaluation 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, 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’s parent(s)/LAR(s) via informed consent and have prior approval 
from the Sponsor (or its designee). 
This study will be conducted in compliance with the protocol, GCP, and all applicable regulatory 
requirements (Section 11.1.1). 
4.1.1.1. 
Screening Period 
Participants will undergo screening assessments to determine study eligibility. Screening 
assessments (Table 1) must be completed after the participant’s parent(s)/LAR(s) signs the ICF. 
The investigator will review study entry criteria to determine participant eligibility during the 
screening period. 
Screening Visit and Day 1 may be combined on the same day. Additionally, the Screening Visit 
may be performed over multiple visits if performed within the 28-day screening window 
(Table 1). 

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Eligible participants will enter the Treatment Period. 
4.1.1.2. 
Treatment and Follow-up Period 
In both Parts 1 and 2, on Day 1, after the completion of the scheduled assessments (Table 1), 
participants will be administered a single IM dose of the IP mRNA-1273.214 (at the applicable 
dose based on study part and arm) or placebo. Placebo will be administered only to those who 
are randomized to the placebo arm in Part 2 of the study. The procedures for IP administration 
will be detailed in the mRNA-1273-P206 Pharmacy Manual.  
Participants will be closely monitored for safety and will remain at the study site for observation 
for at least 60 minutes after dosing in Part 1 and 30 minutes after dosing in Part 2. On Day 57, 
the second dose of IP will be administered. If the visit for the second dose (Day 57) is disrupted 
and cannot be completed at Day 57 (–14/+7 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”) or due to extenuating 
circumstances (to be evaluated by the Sponsor on a case-by-case basis), the visit window may be 
extended to Day 57 + 14 days. When the extended visit window is used, the remaining study 
visits should be rescheduled to follow the intervisit interval from the actual date of the second 
dose. 
Participants will be followed for 12 months after the second dose of IP. To test for the presence 
of SARS-CoV-2 by RT-PCR, nasal swab samples will be collected on each day of injection prior 
to dosing (Day 1 and Day 57), and on Day 85 (28 days after Dose 2), Day 237 (6 months after 
Dose 2), and Day 422 (12 months after Dose 2) according to the SoA (Table 1). 
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 a 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, if severe, reported in an expedited time frame to the Sponsor 
(Section 8.11.4). 
All participants will be monitored for safety and reactogenicity. All participants in the study will 
provide blood specimens for immunogenicity assessments on Day 1 (prior to the first dose), 
Day 85 (28 days after Dose 2), Day 237 (6 months after Dose 2), and Day 422 (12 months after 
Dose 2). 
4.2. 
Scientific Rationale for Study Design 
This Phase 2 study is designed as a two-part, dose-finding and open-label (Part 1), and 
randomized, observer-blinded, and placebo-controlled study (Part 2) to demonstrate the 

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immunogenicity and safety of the mRNA-1273.214 vaccine in participants aged 12 weeks to 
< 6 months. This pediatric study is intended to confirm safety in infants between 12 weeks to 
< 6 months of age and bridge immunogenicity between infants and adults (> 18 years of age) 
enrolled in the pivotal adult Phase 3 study (Study mRNA-1273-P301). It is necessary to 
demonstrate noninferiority of the induced immune response in infants compared with that in 
adults to infer vaccine effectiveness in this age group. 
Part 1 of the study is designed to dose escalate starting with a low dose level in Arm 1. Arm 2 
will test the next higher dose level if there are no safety concerns (after IST review of 
25 participants in Arm 1 who have reached Day 64). Safety and immunogenicity analysis after 
both Arm 1 and Arm 2 have completed enrollment and participants have reached Day 85 will 
determine the dose level for Part 2. Part 2 of the study is designed to assess safety and 
immunogenicity of the selected dose level from Part 1 in a randomized, placebo-controlled 
design. This randomization and placebo arm is necessary to assess safety since no trials have 
assessed an mRNA vaccine in this age group. 
With SARS‑CoV‑2 expected to be circulating in the general population during the study, all 
participants will provide pre- and post-injection blood samples for analysis of antibodies to 
non-vaccine antigens as described in the SoA (Table 1). In addition, participants will have nasal 
swab samples collected before vaccination according to the SoA. Furthermore, in case of any 
signs or symptoms or MAAEs suggesting SARS‑CoV‑2 infection in a participant, an additional 
nasal swab sample will be collected to confirm the diagnosis of SARS‑CoV‑2 via RT-PCR. 
Additionally, clinical information will be carefully collected to evaluate the severity of the 
clinical case. 
Since it is possible that participants are naturally exposed to SARS‑CoV‑2 through community 
exposure, the nasal swab samples collected before study injection and the serologic assays 
performed for Ab responses to non-vaccine antigen(s), may help to discriminate between natural 
infection and vaccine-induced Ab responses, should such discrimination be needed. 
4.3. 
Justification for Dose, Control Product, and Choice of Study 
Population 
In Study mRNA-1273-P204, a 50 and a 25 μg, 2-dose primary series of mRNA-1273 given to 
children aged 6 to 12 years of age and 6 months to 6 years of age, respectively, elicited a robust 
nAb response with a favorable safety profile. Based on these results, the dose for children aged 
12 weeks to < 6 months is anticipated to be 10 μg. Hence in this study, Part 1 will be conducted 
for dose selection of mRNA-1273.214 for participants aged 12 weeks to < 6 months given as a 
2-dose primary series starting with a lower dose of 5 μg, which will serve as a sentinel dose for 

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safety evaluation and to support determination of end-of-shelf life limits for the target 10 μg 
dose.  
A normal saline formulation was chosen as the control product in Part 2 in order to ascertain the 
safety of mRNA-1273.214 in this age group. 
As participants aged 12 weeks to < 6 months are anticipated to be new vaccine recipients over 
time and with this period of life coinciding with waning of maternal antibodies, this age group 
was chosen for this study evaluating pediatric bivalent primary and booster vaccination for 
COVID-19. 
4.4. 
End of Study Definition 
The end of the study for the full study is defined as completion of the last visit of the last participant 
in the study or the last scheduled procedure as shown in the SoA (Table 1) for the last participant 
in this study. 

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5. 
STUDY POPULATION 
Prospective approval of protocol deviation(s) to recruitment and enrollment criteria, also known 
as protocol waivers or exemptions, is not permitted. 
5.1. 
Inclusion Criteria 
Participants are eligible to be included in the study only if all the following criteria apply: 
1. The participant is male or female, between 2 and < 6 months of age at the time of consent 
(Screening Visit), who is in good general health, in the opinion of the investigator, based 
on review of medical history and screening physical examination. 
a) Participant must be at least 12 weeks completed age and must not have completed 
6 months at the time of administration of first dose.  
b) If the participant has a chronic, stable disease, they may be eligible to enroll in 
Part 2, but ineligible for Part 1. The chronic condition (eg, gastroesophageal 
reflux disease) should be stable, per investigator assessment, so that the 
participant can be considered eligible for inclusion in Part 2. Note: a change in 
medication for dose optimization, change within class of medication, reduction in 
dose or increase in dose due to expected weight gain are not considered signs of 
instability. 
2. The participant was born at ≥ 37 weeks gestation (Part 1) or ≥ 34 weeks gestation 
(Part 2), with a minimum birth weight of 2.5 kg, without fetal growth restriction, and the 
participant’s height and weight are both at or above the second percentile for age 
according to the CDC/WHO Child Growth Standard (Section 11.1.18) at the Screening 
Visit. 
3. In the investigator’s opinion, the parent(s)/LAR(s) understand and are willing and 
physically able to comply with protocol-mandated follow-up, including all procedures, 
and provide written informed consent. This includes inability to collect minimum amount 
of sample volume at baseline blood draw.  
5.2. 
Exclusion Criteria 
Participants will be excluded from the study if any of the following criteria apply: 
1. The participant has a known history of symptomatic SARS-CoV-2 infection within 
2 weeks prior to administration of IP or has a known close contact (as defined in 
Section 8.10.2) in the past 2 weeks to someone diagnosed with SARS-CoV-2 infection or 

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COVID-19. Participants may be rescreened after 14 days provided that they remain 
asymptomatic. 
2. The participant is acutely ill or febrile 72 hours prior to or at the Screening Visit. 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. The participant has previously been administered an investigational or approved CoV (eg, 
SARS-CoV-2, SARS-CoV, MERS-CoV) vaccine. 
4. The participant has undergone treatment with investigational or approved agents for 
prophylaxis against COVID-19 (eg, receipt of SARS-CoV-2 monoclonal antibodies) 
within 90 days prior to enrollment. 
5. The participant has a known hypersensitivity to a component of the vaccine or its 
excipients. Hypersensitivity includes, but is not limited to, anaphylaxis or immediate 
allergic reaction of any severity to any of the components of mRNA COVID-19 vaccines 
(including PEG or immediate allergic reaction of any severity to polysorbate). 
6. The participant has a medical, psychiatric, or occupational condition, including reported 
history of substance abuse, in the infant or in the parent(s)/LAR(s) that, according to the 
investigator’s judgment, may pose additional risk as a result of participation, interfere 
with safety assessments, or interfere with interpretation of results. 
7. The participant has a history of diagnosis or condition that, in the judgment of the 
investigator, may affect study endpoint assessment or compromise participant safety, 
specifically the following: 
a) Congenital or acquired immunodeficiency 
b) Chronic hepatitis or suspected active hepatitis 
c) A bleeding disorder that is considered a contraindication to IM injection or 
phlebotomy, or non-receipt of vitamin K at birth  
d) Dermatologic conditions that could affect local solicited AR assessments 
e) Any prior diagnosis of malignancy  
f) Febrile seizures 
 
 
 

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8. The participant has received the following: 
a) Any routine vaccination with inactivated or live vaccine(s) within 14 days prior to 
first or second vaccination or plans to receive such a vaccine within 14 days of 
any study vaccination. 
b) Systemic immunosuppressants or immune-modifying drugs (including maternal 
use during pregnancy or lactation) for > 14 days in total within 6 months prior to 
the day of enrollment (for corticosteroids, ≥ 1 mg/kg/day or, if participant weighs 
> 10 kg: ≥ 10 mg/day prednisone equivalent). 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. 
c) Intravenous or subcutaneous blood products (red blood cells, platelets, 
immunoglobulins) within 3 months prior to enrollment. 
9. The participant has participated in an interventional clinical study within 28 days prior to 
the Screening Visit or plans to do so while participating in this study, or maternal 
participation in an interventional clinical study during pregnancy. 
10. The participant is an immediate family member, or household contact, of an employee of 
the study site or Sponsor or someone otherwise directly involved with the conduct of the 
study. As applicable, family members/household contacts of employees of the larger 
institution or affiliated private practice not part of the study site may be enrolled. 
11. The participant is a child who has been placed under the control or protection of an 
agency, organization, institution or entity by the courts, the government, or a government 
body, acting in accordance with powers conferred on them by laws and regulation. Does 
not include a child who is adopted or has an appointed legal guardian. 
5.3. 
Screen Failures 
Screen failures are defined as participants whose parent(s)/LAR(s) provide consent to participate 
in the study but are not subsequently assigned (Part 1) or randomly assigned (Part 2) to 
treatment. A minimal set of screen failure information is required to ensure transparent reporting 
of screen failure participants to meet the Consolidated Standards of Reporting Trials publishing 
requirements and to respond to queries from regulatory authorities. Minimal information 
includes date of informed consent, demography, reason(s) for screen failure, eligibility criteria, 
and information on any SAE that may have occurred after dosing to the time of withdrawal. 
Individuals who do not meet the criteria for participation in this study (screen failure) may be 
rescreened one time if they will be eligible upon rescreening. 

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On Day 1, blood sample for immunogenicity assessment must be collected prior to 
randomization and dosing. In both Part 1 and Part 2 of study, if a Day 1 (baseline) blood sample 
cannot be obtained, the participant could be rescheduled within the allowable screening period 
one time. If a blood sample still cannot be obtained at the rescheduled visit, then the participant 
will be considered a screen failure due to inability to satisfy inclusion criterion 3. 

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6. 
STUDY TREATMENT 
6.1. 
Investigational Products Administered 
The term IP refers to both the mRNA-1273.214 vaccine and placebo (0.9% sodium chloride) 
administered in this study. 
mRNA-1273.214 is a bivalent vaccine containing mRNA-1273 and mRNA-1273.529, 
co-formulated at a 1:1 ratio. mRNA-1273 is an LNP dispersion containing the mRNA encoding 
for the prefusion stabilized S protein (S-2P) of SARS-CoV-2 of Wuhan-Hu-1. mRNA-1273.529 
is an LNP dispersion containing the mRNA encoding for the S-2P of the SARS-CoV-2 Omicron 
variant (B.1.1.529). Each mRNA is formulated in a mixture of 4 lipids common to the Sponsor’s 
mRNA vaccine platform: SM-102; cholesterol; 1,2-distearoyl-sn-glycero-3-phosphocholine 
(DSPC); and 1,2-dimyristoyl-rac-glycero-3-methoxypolyethylene glycol-2000 (PEG2000-
DMG). mRNA-1273.214 injection is provided as a sterile liquid for injection and is a white to 
off-white dispersion at a concentration of 
 mg/mL in 20 mM Tris buffer with sucrose and at 
pH 7.5. 
6.2. 
Randomization and Blinding 
Random assignment of participants in Part 2 of the study will use a centralized IRT, in 
accordance with pregenerated randomization schedules. Approximately 600 participants will be 
randomized in a 1:1 ratio to the mRNA-1273.214 arm or placebo arm (n = ~300 participants in 
each group). 
As the appearance of the study treatments differs, enrollment will be observer blinded as to 
treatment assignment.  
No set of individual treatment codes will be held at the study sites. 
Neither the participant nor participant’s parent(s)/LAR(s), nor the investigator nor clinical staff 
responsible for study assessments/safety will have access to the treatment assignment during the 
conduct of the study. 
Dose preparation, administration, and accountability will be performed by designated unblinded 
site personnel who will not participate in any of the clinical study evaluations. The unblinded site 
personnel will prepare the dose out of view of the participant's parent(s)/LAR(s) and the blinded 
site personnel, and will administer the vaccine in a separate room, or at minimum, using a curtain 
to shield view of the injected arm/leg. The unblinded site personnel will not be involved in 
participant evaluations and will not reveal the identity of the IP to either the participant’s 
parent(s)/LAR(s) or the blinded clinic personnel involved in the conduct of the study unless this 
information is necessary in the case of an emergency. Once the injection is completed, only the 
CCI

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blinded clinic staff will perform further assessments and interact with the participant’s 
parent(s)/LAR(s). Access to the randomization code will be strictly controlled at the pharmacy. 
The laboratory personnel in charge of immunogenicity testing will be blinded to the treatment 
assignment of the samples tested throughout the course of the study. 
Except in the case of medical necessity, a participant’s treatment should not be unblinded 
without the approval of the Sponsor. The treatment code should be broken only if the 
investigator in charge of the participant feels that the case cannot be treated without knowing the 
identity of the study vaccine. Instructions regarding emergency unblinding will be provided to 
the investigator and are discussed in Section 6.3.8. 
The investigator, clinic staff, study participant’s parent(s)/LAR(s), site monitors, and Sponsor 
personnel (or its designees) will be blinded to the IP administered until the study database is 
locked and unblinded for the final analysis. At the planned analyses (see Section 9.6), 
pre‑identified Sponsor team members and selected CRO team members will be unblinded to 
conduct the analyses. Study participant’s parent(s)/LAR(s), investigators, and blinded site 
personnel will remain blinded. 
6.3. 
Preparation/Handling/Storage/Accountability 
6.3.1. 
Clinical Study Material Preparation 
Each dose of IP will be prepared for each participant based on the assigned treatment, as detailed 
in the mRNA-1273-P206 Pharmacy Manual.  
6.3.2. 
Clinical Study Material Administration 
Each participant will receive 2 doses of IP by IM injection approximately 8 weeks apart (Day 1 
and Day 57) in Part 1 and Part 2 of study. The IM injections will be administered into the 
anterolateral thigh, according to their assigned regimen and according to the procedures specified 
in the mRNA-1273-P206 Pharmacy Manual. 
At each visit when IP is administered, participants will be monitored for a minimum of 
60 minutes after administration in Part 1 and 30 minutes after administration in Part 2. 
Assessments will include body temperature measurements (must be measured via the axillary 
route and any axillary reading of ≥ 37.8°C/≥ 100°F may be confirmed by a rectal measurement) 
and monitoring for local or systemic reactions. 
Eligibility for the subsequent dose of IP will be determined by the criteria outlined in Section 7. 
The study sites will be appropriately staffed with individuals with basic pediatric 
cardiopulmonary resuscitation training/certification. Either on-site resuscitation equipment and 

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personnel or appropriate protocols for the rapid transport of participants to a resuscitation area or 
facility are required. 
6.3.3. 
Clinical Study Material Delivery and Receipt 
The description of the IP and instructions for the receipt, storage, preparation, administration, 
accountability, and destruction of the IP are described in the mRNA-1273-P206 Pharmacy 
Manual. 
6.3.4. 
 Clinical Study Material 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 2R borosilicate glass vials. The IP will have all required 
labeling per regulations and will be supplied to the pharmacy in an unblinded manner. 
The IP will be packaged and labeled in accordance with the standard operating procedures of the 
Sponsor or its designee, CFR Title 21, Good Manufacturing Practice guidelines, ICH GCP 
guidelines, guidelines for Quality System Regulations, and applicable regulations. 
6.3.5. 
Clinical Study Material Storage 
The IP must be stored as per the temperature conditions printed on the IP label in a secure area 
with limited access and be protected from moisture and light until it is prepared for 
administration (Section 6.3.1). The freezer should have automated temperature recording and a 
24-hour alert system in place that allows for rapid response in case of freezer malfunction. There 
must be an available back-up freezer. The freezer must be connected to a back-up generator, or 
an alternate plan must be in place in the event of a power failure. 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. 
6.3.6. 
Clinical Study Material 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 each part of the study. Additional details are found in the mRNA-1273-P206 
Pharmacy Manual. 

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6.3.7. 
Clinical Study Material Handling and Disposal 
A study site monitor will reconcile the IP inventory during the conduct and at the end of each 
part of the study for compliance. Once fully reconciled after each monitoring visit at the study 
site, the IP can be destroyed at the investigational site or by 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. For further direction, refer to mRNA-1273-P206 Pharmacy Manual. 
6.3.8. 
Unblinding 
Except in the case of medical necessity, a participant’s treatment assignment in Part 2 should not 
be unblinded without the approval of the Sponsor. If a participant becomes seriously ill during 
the study, the blind will be broken only if knowledge of the treatment assignment will affect that 
participant’s clinical management. In the event of a medical emergency requiring identification 
of individual treatment assignment, the investigator will make every attempt to contact the CRO 
clinical research associate (who must inform the Sponsor medical lead) to explain the need for 
unblinding within 24 hours of opening the code. The investigator will be responsible for 
documenting the time, date, reason for unblinding, and the names of the personnel involved. The 
investigator (or designee) will have access to unblind participants within IRT. All unblindings 
will be tracked via an audit trail in IRT and documented in the final study report. 
If a COVID-19 vaccine (mRNA-1273 or other) is authorized or licensed for infants, 
parent(s)/LAR(s) of eligible study participants (by virtue of their age) will be offered the 
opportunity to unblind via a phone call and learn what treatment the participant received, ideally 
after they have reached at least Day 85 in the study. Participants who have received 
mRNA-1273.214 will continue in the study and will be followed per protocol. If a participant 
previously received placebo, then their parent(s)/LAR(s) will be advised to discuss with the 
participant’s primary care physician and follow current CDC recommendations regarding 
COVID-19 immunization. If a participant who received placebo in the study chooses to receive a 
nonstudy COVID-19 vaccine, they will be withdrawn from the study. 
6.4. 
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 doses, the reason for the missed dose will be 
recorded. Data will be reconciled with study site accountability records to assess compliance. 

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Participants who miss the second 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 
whose parent(s)/LAR(s) withdraws or if the participant 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. If a participant does not 
complete a visit within the time window, that visit may be performed out of window or may be 
classified as a missed visit per investigator discretion. If classified as a missed visit, 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. 
6.5. 
Prior and Concomitant Medications 
6.5.1. 
Maternal Medications and Therapies 
Information about the participant’s mother’s COVID-19 vaccine(s) and COVID-19 infection(s) 
before conceiving the participant, while pregnant with the participant, and while breastfeeding the 
participant will be recorded in the participant’s eCRF. 
6.5.2. 
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 their 
parent(s)/LAR(s) provided informed consent (or as designated in the inclusion/exclusion 
requirements) will be recorded in the participant’s eCRF. 
6.5.3. 
Concomitant Medications and Therapies 
At each study visit, study site staff must question the participant’s parent(s)/LAR(s) 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 and throughout the study period, including: 
o Any authorized or investigational COVID-19 vaccine 
o Routine pediatric vaccines including but not limited to hepatitis B, rotavirus, 
Hib, DTaP, PCV13, IPV, MMR, varicella, hepatitis A 

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o Seasonal influenza vaccine administered for the current influenza season 
(typically October through April in the Northern Hemisphere).  
• All concomitant medications taken through 28 days after each dose of IP (through the 
completion of the Day 85 visit). Antipyretics and analgesics taken prophylactically (ie, 
taken in the absence of any symptoms in anticipation of an injection reaction) will be 
recorded as such. 
• All concomitant immunosuppressants or immune-modifying drugs potentially transferred 
through breastmilk throughout the study period. 
• Any concomitant medications used to prevent or treat COVID-19 or its symptoms. 
• Any concomitant medications relevant to or for the treatment of an AESI, SAE, or an 
MAAE throughout the study period. 
• Participant’s parent(s)/LAR(s) will be asked in the eDiary if the participant has taken any 
antipyretic or analgesic to treat or prevent fever or pain within 7 days after each IP 
injection, including on the day of injection. Reported antipyretic or analgesic medications 
should be recorded in the source document by the study site staff during the clinic visits 
after vaccination or via other interactions with participant’s parent(s)/LAR(s) (eg, 
telephone calls). 
Data regarding nutritional supplements, eg, vitamins, probiotics, and herbal supplements, will 
not be collected unless relevant to an AE. 
Concomitant medications (including vaccinations) will be coded using the WHODrug 
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 
concomitant medications are adequately recorded in the eCRF. 
6.5.4. 
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, but may determine a participant’s eligibility to receive a second 
dose or be included in the PP analysis. Analysis sets are described in Section 9.4. 

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• 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, 
> 14 days in total), including through breastmilk, during the study period. For 
corticosteroids, receipt of prednisone or the equivalent at a dose of ≥ 1 mg/kg/day (or 
≥ 10 mg/day if participant weighs > 10 kg) 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 Ab-containing blood products (eg, packed red blood cells) 
administered during the study period. 

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7. 
DELAY OR DISCONTINUATION OF STUDY INTERVENTION 
AND PARTICIPANT DISCONTINUATION/WITHDRAWAL 
7.1. 
Criteria for Delay of Vaccine Administration 
7.1.1. 
Individual Participant Criteria for Delay of Study Vaccination 
Body temperature must be measured on dosing visits before vaccine administration (body 
temperature must be measured via the axillary route and any axillary reading of 
≥ 37.8°C/≥ 100°F may be confirmed by a rectal measurement). The following events constitute 
criteria for delay of injection, and if any 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 SoA (Table 1), or the participant may be discontinued from dosing at the discretion of the 
investigator (Section 7.2): 
• 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 a participant was exposed to a household contact (excluding school or other exposures) who 
tested positive for SARS-CoV-2 after the participant received the first dose, the administration of 
the second dose may be delayed to allow for at least 14 days between the positive test or the last 
day of symptoms (if present) of the household contact and Dose 2 as long as the participant 
remains asymptomatic. 
If a participant tests positive for SARS-CoV-2 after having received Dose 1 but remains 
asymptomatic and the second dose is due before 14 days after the positive test, administration of 
the second dose may be delayed to allow for at least 14 days between the participant’s positive 
test and Dose 2 as long as participant remains asymptomatic. 
If a participant tests positive for SARS-CoV-2 after having received Dose 1 and develops 
symptoms of COVID-19, the participant may still receive a second dose, but the second dose 
should be delayed until approximately 90 days after diagnosis with COVID-19. 

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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 6.5.3). 
7.2. 
Discontinuation of Study Vaccination 
Participant’s parent(s)/LAR(s) can choose to 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 or delay a 
participant from further injection under the following circumstances: 
• The participant’s parent(s)/LAR(s) withdraw consent. 
• The participant develops, during the course of the study, symptoms or conditions listed 
in the exclusion criteria (Section 5.2). 
• The participant experiences an AE (other than solicited reactogenicity) after injection 
that is considered by the investigator to be related to IP (Section 8.11.8) and is assessed 
as severe (Section 8.11.7). 
• The participant 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. 
• The participant experiences an AESI (Section 11.2). 
• The participant experiences a clinically significant change in general condition that, in 
the judgment of the investigator, requires vaccine withdrawal. 
• The participant experiences anaphylaxis (described in Section 8.11.4) clearly related to 
IP. 
• The participant experiences a hypersensitivity reaction related to IP. 
The reason(s) for withdrawal from further injection must be recorded in the eCRF. 
If a participant takes a prohibited drug therapy, the investigator could withhold the second dose 
based on a joint decision of the investigator and the CRO’s medical monitor (Section 6.5.3). 
Every reasonable attempt should be made to follow up with participants for safety throughout the 
entire scheduled study period according to the SoA (Table 1), even if the participant does not 
receive the second dose or misses 1 or more visits. Unless the participant’s parent(s)/LAR(s) 
withdraw consent, the participant is expected to remain in the study and complete all scheduled 
visits and assessments. 

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7.3. 
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 participant’s parent(s)/LAR(s) can withdraw consent and withdraw the participant from the 
study at any time during the study, 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’s parent(s)/LAR(s) desires to withdraw the participant from the study because of an 
AE, the investigator will try to obtain agreement to follow up with the participant’s 
parent(s)/LAR(s) until the event is considered resolved or stable and will then complete the end 
of the study 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’s parent(s)/LAR(s) or by the investigator, as well as which of the following possible 
reasons was the cause for withdrawal: 
• AE (specify) 
• SAE (specify) 
• Death 
• LTFU 
• Physician decision (specify) 
• Protocol deviation 
• Study terminated by Sponsor 
• Withdrawal of consent by participant’s parent(s)/LAR(s) 
• Other (specify) 
Participants who are withdrawn from the study because of AEs (including AESIs and SAEs) 
must be clearly distinguished from participants who are withdrawn for other reasons. 
Investigators will follow up with parent(s)/LAR(s) of the participants who are withdrawn from 
the study as result of an SAE or AE until resolution of the event. 

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Any parent(s)/LAR(s) who withdraws the participant from the study may request destruction of 
any samples taken and not tested. The investigator must document this in the study site study 
records and inform the Sponsor. 
If the participant’s parent(s)/LAR(s) withdraw consent for disclosure of future information, the 
Sponsor may retain and continue to use any data collected before such a withdrawal of consent 
(Section 11.1.10). 
The Sponsor will continue to retain and use all research data that have already been collected for 
the study evaluation, unless the participant’s parent(s)/LAR(s) have 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). 
Unblinding of still blinded participants based only on parental/LAR request and not related to a 
safety event or health concern will not be permitted, in order to protect the data integrity of the 
blinded portion of the study. If a parent/LAR wishes to withdraw their child from the study, they 
may withdraw at any time but will only be able to learn the treatment group assignment once an 
unblinding trigger is reached as described in Section 6.3.8. If an unblinding trigger is reached 
and a participant who received placebo in the study chooses to receive a nonstudy COVID-19 
vaccine, they will be withdrawn from the study (Section 6.3.8). 
7.3.1. 
End-of-study Visit (Prior to Day 422) 
Once the parent(s)/LAR(s) withdraw the participant from the study, the investigator (or delegate) 
should confirm all ongoing AEs have been addressed and answer any additional questions the 
participant’s parent(s)/LAR(s) may have; this may be done via a telephone call. The 
communication should be documented in the source. The End-of-Study/Study Discontinuation 
eCRF page must be completed. 
7.4. 
Study Pause Rules 
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 4. 

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Table 4: 
Pause Rule Criteria, Events, and Thresholds 
Pause Rule 
Criterion 
Event 
Participant Threshold for 
Triggering Study Pause 
Pause Rule Assessed by Investigator 
1 
Any SAE that cannot be reasonably attributed to a 
cause other than the study vaccination 
≥ 1 
Pause Rules to be Assessed by Medical Monitoring Team (Sponsor/CRO) 
2a 
Individual Grade 3 or higher solicited local AR 
lasting ≥ 24 hours in duration and occurring within 
7 days of injection (Days 1 to 7)b 
At least 2 participants and ≥ 5% 
of the dosed participants in each 
arm 
3a 
Individual Grade 3 or higher solicited systemic AR 
lasting ≥ 24 hours in duration that cannot be 
reasonably attributed to a cause other than the 
study vaccination, within 7 days of injection 
(Days 1 to 7)b 
At least 2 participants and ≥ 5% 
of the enrolled participants in 
each arm 
4 
Any severe unsolicited AE that cannot be 
reasonably attributed to a cause other than the 
study vaccination, within the 7-day (Days 1 to 7) 
post-vaccination period 
At least 2 participants and ≥ 5% 
of the enrolled participants in 
each arm 
Abbreviations: AE = adverse event; AR = adverse reaction; CRO = contract research organization; 
eDiary = electronic diary; SAE = serious adverse event. 
a. 
“Individual AR” is defined as 1 AR type, eg, pain, erythema, or headache could each be an “individual AR.” 
b. 
This will be tracked in the following manner: if a participant reports a Grade 3 or higher AR in 2 consecutive 
eDiary entries within 22 to ≥ 24 hours apart, the participant will be contacted and asked whether the AR lasted 
≥ 24 hours in duration. If an eDiary entry is not entered the day after a Grade 3 or higher AR was reported, the 
participant will also be contacted and asked whether the AR lasted ≥ 24 hours in duration. 
If any of the thresholds for a study pause are met, the Sponsor will immediately suspend further 
enrollment and/or study dosing by notifying all investigators and the DSMB will convene on an 
ad hoc basis. The DSMB will review all available unblinded study data (as applicable) to help 
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. 
The investigator or designee is responsible for reporting each event that potentially meets any 
pause rule criterion within 24 hours of observation to the Sponsor. The Sponsor will inform the 
DSMB of any event that potentially meets the pause rule criterion. The DSMB will review all 

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available study data to help adjudicate such events in accordance with the DSMB charter 
(Section 8.12.2). 
The Sponsor will notify the Center for Biologics and Evaluation Research within 48 hours in the 
event of a study pause. In the event of a study pause, all safety and immunogenicity assessments 
will continue per protocol. The window allowance for injection visits may be extended by an 
additional 7 days (ie, + 21 days) for affected participants at the discretion of the Sponsor. 
7.5. 
Lost to Follow-up  
A participant will be considered LTFU if the participant’s parent(s)/LAR(s) repeatedly fail 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’s parent(s)/LAR(s) and 
reschedule the missed visit as soon as possible, counsel the participant’s parent(s)/LAR(s) 
on the importance of maintaining the assigned visit schedule and ascertain whether they 
wish the participant 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’s parent(s)/LAR(s) (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 whose parent(s)/LAR(s) continue to be unreachable or continue 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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8. 
STUDY ASSESSMENTS AND PROCEDURES 
Participants will undergo study procedures at the time points specified in the SoA (Table 1). 
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’s parent(s)/LAR(s) 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 exception of Screening, Day 1, Day 57, Day 85, 
Day 237, and Day 422) with the approval of the Sponsor (home visits also require site IRB 
approval). 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. 
8.1. 
Screening 
Before performing any study procedures, parent(s)/LAR(s) of all potential participants will sign 
an ICF (as detailed in Section 11.1.6). 
At the Screening Visit (up to 28 days for the Day 1 visit), all screening requirements, including 
reason for screen failure if a participant is not randomized, must be completed. The Enrollment 
Page in the eCRF must also be completed. 
The Screening Visit and Day 1 may be performed on the same day or a different day. 
Additionally, the Screening Visit may be performed over multiple visits if within the 28‑day 
screening window. Procedures conducted as part of the participant’s routine clinical management 
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 (Table 1). 
8.2. 
Confirm Inclusion and Exclusion Criteria 
All inclusion and exclusion criteria described in Section 5.1 and Section 5.2 must be met before 
randomization (Day 1 visit). 

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8.3. 
Demographic and Baseline Data 
Demographic information relating to the participant’s sex, age, race, ethnicity, height, and 
weight will be recorded at the Screening Visit on the appropriate eCRF page. Maternal history of 
SARS-CoV-2 infection, COVID-19 immunization, as well as pregnancy, labor, and delivery 
details will also be recorded at the Screening Visit on the appropriate eCRF page. 
8.4. 
Medical History 
Medical history will be collected and recorded for each participant and the participant’s mother 
on the appropriate eCRF page. Significant findings that were present prior to the signature of the 
informed consent must be included in the Medical History eCRF page. 
8.5. 
Randomization 
Vaccination group allocation in Part 2 will be performed at the Day 1 visit as described in 
Section 6.2. The confirmation for study vaccine administration must be recorded on the 
Exposure page of the eCRF. 
8.6. 
Physical Examination and Vital Signs 
A full physical examination will be performed at the Screening Visit. The full examination will 
include length/height and weight measurements and assessment of skin, head, ears, eyes, nose, 
throat, neck, lungs, heart, abdomen, lymph nodes, and musculoskeletal system/extremities. 
Symptom‑directed physical examinations may be performed at other clinic visits. Interim 
physical examinations will be performed at the discretion of the investigator. Any clinically 
significant finding identified by an HCP during clinic visits should be reported as an MAAE 
(Section 8.11.4). 
Vital sign measurements will be assessed at the Screening visit. Vital signs will include the 
assessment of systolic and diastolic blood pressures, heart rate, respiratory rate, and body 
temperature. Body temperature must be measured via the axillary route and any axillary reading 
of ≥ 37.8°C/≥ 100°F may be confirmed by a rectal measurement. On the day of vaccination, vital 
signs will be collected prior to vaccination and only if clinically indicated after vaccination per 
the discretion of the investigator. Vital signs may be collected at other clinic visits in conjunction 
with a symptom‑directed physical examination. 
The information collected will be recorded in the eCRF. 

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8.7. 
Study Vaccine Administration 
A single injection (mRNA-1273.214 or placebo) will be administered to all participants on 
dosing visits as described in the SoA (Table 1). 
After completing all prerequisite procedures prior to vaccination, the study vaccine will be 
administered via IM injection into the anterolateral thigh. Additional details regarding vaccine 
administration procedure are provided in Section 6.3.2. 
The participants will be observed closely (via clinical assessment including measurement of vital 
signs if clinically indicated based on discretion of the investigator) for at least 60 minutes 
(Part 1) or 30 minutes (Part 2) following the administration of the vaccine, with appropriate 
medical treatment readily available in case of anaphylaxis or other hypersensitivity reactions. 
8.8. 
Immunogenicity Assessments 
Blood samples for immunogenicity assessments and biomarker samples will be collected at the 
time points indicated in in the SoA (Table 1). The following analytes will be measured: 
• Serum nAb titer against SARS-CoV-2 as measured by pseudovirus and/or live virus 
neutralization assays, including VOC (Omicron). 
• Serum bAb titer as measured by a multiplex ligand-binding assay specific to the 
SARS‑CoV‑2 S protein. 
• Serum bAb titer as measured by a multiplex ligand-binding assay specific to the 
SARS‑CoV‑2 nucleocapsid protein. 
• Testing for serologic markers for SARS‑CoV‑2 infection as measured by 
anti‑nucleocapsid antibodies detected by immunoassay. 
Sample aliquots will be designed to have back-up samples, if possible; vial volumes will likely 
be adequate for future testing needs. The actual time and date of each sample collected will be 
recorded in the eCRF, and 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 laboratory manual. 
Measurement of bAb and nAb levels will be performed in a laboratory designated by the 
Sponsor. 
According to the ICF (Section 11.1.6), serum from immunogenicity testing may be used for 
future research, which may be performed at the discretion of the Sponsor to further characterize 

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the immune response to SARS-CoV-2, additional assay development, and the immune response 
across SARS-CoV-2 viruses. 
8.9. 
Vaccine Effectiveness Assessments and Surveillance for COVID-19 
Symptoms 
8.9.1. 
Vaccine Effectiveness Assessments 
Vaccine effectiveness for participants will be inferred based on serum Ab responses obtained on 
Day 85 (28 days after the second injection of mRNA‑1273.214 primary series). Inference will be 
based on assessing the Ab responses against the geometric mean (GM) value of serum Ab and 
SRR after mRNA-1273 primary series in adults (Study mRNA‑1273-P301). The statistical 
parameters to infer effectiveness are described in Section 3. 
8.9.2. 
COVID-19 Case Definitions 
The incidence of COVID-19 will be assessed as an exploratory objective in Part 2 of this study. 
Active surveillance for COVID‑19 and SARS-CoV-2 infection will be performed in both parts of 
the study (see Table 5 and Table 6). 
To be considered as a case of COVID-19, the following case definition must be met: 
• The participant must have at least 1 nasal swab (or respiratory sample, if hospitalized) 
positive for SARS-CoV-2 by RT-PCR AND 
• ONE of the following: 
− Fever (temperature ≥ 38ºC/≥ 100.4ºF) or chills (of any duration, including ≤ 4 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 
− Abdominal pain 
− Nausea or vomiting 

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− Diarrhea 
− Poor appetite/poor feeding 
Severe COVID-19: 
To be considered severe COVID-19, the following criteria must be met: 
• Confirmed COVID-19 as per the COVID-19 case definition, plus any of the following: 
− Meeting criteria for systemic inflammatory response syndrome based on age-specific 
variables (Table 5) OR 
− Respiratory failure or acute respiratory distress syndrome (defined as needing 
high-flow oxygen, noninvasive or mechanical ventilation, or extracorporeal 
membrane oxygenation), medical intervention for shock (intravenous fluids, 
vasopressors, etc), OR 
− Significant acute renal, hepatic, or neurologic dysfunction (Table 6), OR 
− Admission to an ICU or death. 
Table 5: Age-specific Cutoffs for Vital Signs and Laboratory Variables 
Age Group 
Heart Rate, 
Beats/Min 
Respiratory 
Rate, 
Breaths/Min 
Leukocyte 
Count, 
Leukocytes × 
103/mm3 
Systolic Blood 
Pressure, 
mm Hg 
Tachycardia Bradycardia 
1 month to 1 year 
> 180 
< 90 
> 34 
> 17.5 or < 5 
< 70  
> 1 year to 
5 years 
> 140 
NA 
> 22 
> 15.5 or < 6 
< 70 + (age in 
years × 2)  
Abbreviations: AHA = American Heart Association; NA = not applicable. 
Note: Lower values for heart rate or leukocyte count are for the fifth percentile and upper values for heart rate, 
respiratory rate, or leukocyte count are for the 95th percentile for the age group. Systolic blood pressure values are 
based on AHA definitions of hypotensive shock for pediatric population. 
Source: Goldstein et al 2005 and Topjian et al 2020. 

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Table 6: Definition of Renal, Liver, and Neurological Dysfunction for Pediatric 
Population (< 12 years of age) 
Acute Renal 
Dysfunction  
• 
Increase in serum creatinine by ≥ 0.3 mg/dL (≥ 26.5 µmol/L) within 48 hours 
OR  
• 
Increase in serum creatinine to ≥ 1.5 × baseline, known or presumed to have 
occurred within prior 7 days 
OR  
• 
Urine volume ≤ 0.5 mL/kg/hour for 6 hours 
Acute Liver 
Dysfunction 
• 
> 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 
Acute 
Neurological 
Dysfunctiona 
ANY of the following: 
• 
Loss of sense of smell or taste 
• 
Seizures or status epilepticus 
• 
Severe headache (preventing normal daily activities) 
• 
Persistent difficulty walking or crawling (if crawling/walking before) 
• 
Persistent altered awareness or confusion (preventing normal daily activities) 
• 
Persistent severe fatigue or weakness (preventing normal daily activities) 
Abbreviations: ALP = alkaline phosphatase; ALT = alanine aminotransferase; AST = aspartate aminotransferase; 
GGT = gamma-glutamyl transferase.  
Source: a LaRovere et al 2021. 
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 
as follows: 
− bAb level against SARS-CoV-2 nucleocapsid protein negative at Day 1 that becomes 
positive postbaseline, OR 
− Positive RT-PCR postbaseline. 

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8.9.3. 
Surveillance for COVID-19 Symptoms 
Surveillance for COVID-19 symptoms will be conducted via biweekly telephone calls or eDiary 
prompts as specified in Section 8.10.2 and Figure 2; starting after participant enrollment and 
continuing throughout the study. 
If there is no response to an eDiary prompt for 2 days, the study site staff will contact the study 
participant by telephone. 
According to the CDC, as of 22 Dec 2020 (CDC 2020a), 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 pre-specified symptoms that meet the criteria for 
suspicion of COVID-19 will be elicited periodically (Section 8.10.2 and Section 8.9.4) from the 
participant, and the presence of any one of these symptoms (in the absence of an alternative 
diagnosis) 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 a nasal swab for SARS-CoV-2 within 
72 hours, or as soon as possible thereafter. 
• 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 
• Abdominal pain 
• Nausea or vomiting 
• Diarrhea 
• Poor appetite/poor feeding 

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Figure 2: 
Surveillance for COVID-19 Symptoms and the Corresponding Clinical Data 
Pathways 
 
Abbreviations: COVID-19 = coronavirus disease 2019; HCP = healthcare practitioner; PCR = polymerase chain 
reaction; RT-PCR = reverse transcriptase polymerase chain reaction; SARS-CoV-2 = severe acute respiratory 
syndrome coronavirus 2. 
Note: Blood sample for SARS-CoV-2 surveillance not shown in figure. 
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-1273.214 (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 a nasal swab should be collected. The 
collection of a nasal swab prior to the first dose on Day 1, prior to the second dose on Day 57, 
and then at all subsequent study visits (Day 85, Day 237, and Day 422) can help ensure that 
cases of COVID-19 are not overlooked. Any study participant who reports respiratory symptoms 

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during the 7-day period after vaccination without an alternative diagnosis should be evaluated for 
COVID-19. 
For children with febrile illnesses, if an alternative diagnosis is identified (eg, positive urine 
culture, streptococcal pharyngitis, cellulitis), the investigator may decide to omit the illness visit. 
Identification of an alternative viral agent (such as respiratory syncytial virus or influenza by 
rapid testing) does not satisfy this requirement, as co-infections with SARS-CoV-2 may occur. 
An investigator may elect to omit the illness visit if standard-of-care testing prior to the illness 
visit reveals a negative COVID-19 NAAT performed at a CLIA-certified or CLIA-waived 
laboratory (or a laboratory of equivalent accreditation if the test was done outside the US) and 
the principal investigator can obtain a copy of the negative test. Home testing kits cannot be used 
to satisfy this testing requirement. Standard-of-care evaluation of household contacts that reveals 
a negative COVID-19 is not sufficient to omit an illness visit in the study participant. 
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 trained staff from the study site will 
conduct a home visit as soon as possible to collect a nasal swab sample (for RT-PCR) for 
evaluation of COVID-19. Both study site visits and home visits are referred to as illness visits 
(Section 8.9.3.1).  
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 RT-PCR at a certified laboratory.  
Investigators are encouraged to try to obtain a respiratory sample during the course of 
hospitalization or immediately after hospital discharge as an unscheduled visit for submission to 
the study central laboratory, if feasible. The investigator should determine if the criteria for 
severe COVID-19 have been met. 
Severe COVID-19 is defined in Section 8.9.2. 
All clinical findings will be recorded in the eCRF. All confirmed cases of symptomatic 
COVID-19 will be captured as MAAEs if an illness visit was conducted at the site or if they 
were evaluated by a healthcare provider, along with relevant concomitant medications and 
details about severity, seriousness, and outcome, and will be collected throughout the study 
period (Section 8.11.4). 

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8.9.3.1. 
Assessment for SARS-CoV-2 Infection 
Study participants will have nasal swab and blood samples collected for SARS-CoV-2 testing at 
the time points specified in in the SoA (Table 1). 
A study illness visit (study site visit or home visit) will be arranged within 72 hours of qualifying 
symptoms or as soon as possible thereafter if a participant experiences any of the following: 
• Signs or symptoms of SARS-CoV-2 infection as defined by the CDC (CDC 2022c) 
• MAAE suggesting a SARS-CoV-2 infection 
At each study illness visit, an initial assessment will be performed to determine general 
appearance. This initial assessment may be performed by physicians, advanced practice nurses, 
physician assistants, or registered nurses. If indicated, a physical examination by a study 
clinician (MD, DO, NP, or PA experienced in pediatric examination) may occur. 
The study illness visit (study site visit or home visit) may collect additional clinical information, 
including assessments such as updated medical history, physical examination, blood sampling 
for clinical laboratory testing, and nasal swab sampling for viral RT‑PCR to evaluate the severity 
of the clinical case. Radiologic imaging studies may be conducted. The study site may also 
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. All findings will 
be recorded in the eCRF. 
Additionally, clinical information will be carefully collected to evaluate the severity of the 
clinical case. 
If a participant experiences an exposure to an individual in the household confirmed to be 
infected with SARS‑CoV‑2 (ie, close contact as defined in Section 8.10.2), an exposure visit 
(study site visit or home visit) will be arranged approximately 7 days after the contact tests 
positive. This exposure will be captured in the COVID-19 exposure form. A negative local 
diagnostic test (NAAT) may be used to satisfy the study visit, provided that the participant 
remains asymptomatic for COVID-19 and the test is collected at least 5 days after the index case 
in a household. In accordance with CDC guidance on COVID-19 testing, exposure visits are not 
required for participants who are within 90 days of a COVID-19 illness (from the date of positive 
COVID-19 test). Illness visits should still be performed, even if within 90 days of a previous 
SARS-COV-2 infection, for participants with signs/symptoms consistent with COVID-19. 
If participants are confirmed to have SARS‑CoV‑2 infection by study clinical laboratory testing, 
the investigator will notify the participant’s parent(s)/LAR(s) and the participant’s primary care 
physician of the diagnosis via fax or other Health Information Portability and Accountability Act 
compliant electronic data transfer (eg, e-mail if applicable). If the study participant does not have 

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a primary care physician, the investigator will assist them to obtain one. The participant and 
participant’s parent(s)/LAR(s) will also be instructed on infection prevention measures consistent 
with local public health guidance. Laboratory test results for SARS‑CoV‑2 infection in study 
participants should be submitted to state or local public health departments according to local 
policy. The investigator must either directly report to state or local public health department or 
obtain confirmation from the participant’s primary care physician that the positive test was 
reported. 
Any confirmed symptomatic SARS‑CoV‑2 infection that occurs in participants assessed at a site 
visit or by another healthcare provider will be captured as an MAAE along with relevant 
concomitant medications and details about severity, seriousness, and outcome. 
If a participant tests positive at baseline but remains asymptomatic, the second dose may still be 
administered as long as the participant remains asymptomatic and no other concerns arise. 
The following alternative process may be used for assessment of SARS-CoV-2 infection: 
• If an illness visit is not feasible due to COVID-19-related restrictions at the site or in the 
wider community, a telehealth visit or phone call combined with a local diagnostic test 
(or home visit by site personnel if permitted [Section 4.1.1]) can substitute for a clinic 
visit. 
• There are currently no rapid antigen tests approved for children < 2 years of age. 
o A negative home rapid antigen test must not be taken as a reason to forgo the 
illness visit. 
o If the participant reports symptoms, or is asymptomatic after a household 
exposure, and the home rapid antigen test was positive, the investigator should 
encourage the family to seek confirmatory polymerase chain reaction-based 
testing at a local testing center or return to the site for an illness visit. 
• If a rapid antigen test becomes authorized/approved for children of the participant’s age, 
the participant’s parent(s)/LAR(s) may perform a home test rather than obtaining a test 
performed by an HCP that may be inaccessible due to COVID-19-related restrictions in 
the community. In such a scenario, the following process should apply: 
o If the participant is asymptomatic but was exposed to a positive household 
member, and the home test obtained within the appropriate window (at least 
5 days post-positive test of household contact) was negative, the investigator may 
accept this result and forego the illness visit. 

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o If the participant reports symptoms but the home test was negative, the 
investigator may forego the illness visit but report the AE as appropriate (eg, 
upper respiratory infection). 
o If the participant reports symptoms, or is asymptomatic after a household 
exposure, and the home test was positive, the investigator should encourage the 
family to seek confirmatory polymerase chain reaction-based testing at a local 
testing center or return to the site for an illness visit. 
8.9.4. 
Follow-up Period After Diagnosis With COVID-19 
Any confirmed symptomatic COVID-19 occurring in a participant assessed at a site visit will be 
captured as an MAAE along with relevant concomitant medications and details about severity, 
seriousness, and outcome. The investigator should determine if the criteria for severe COVID‑19 
have been met. If the participant is hospitalized, 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. 
8.10. 
Safety Assessments 
Safety assessments will include monitoring and recording of the following for each participant, 
according to the SoA (Table 1): 
• Solicited local and systemic ARs (Section 8.11.3) that occur during the 7 days following 
each injection (ie, the day of injection and 6 subsequent days). Solicited ARs will be 
recorded daily using eDiaries (Section 8.10.2). 
• Unsolicited AEs observed or reported during the 28 days following each injection (ie, the 
day of injection and 27 subsequent days). Unsolicited AEs are defined in Section 8.11.1. 
• AEs leading to discontinuation from Day 1 through EoS. 
• MAAEs (Section 8.11.4) from Day 1 through EoS. 
• SAEs (Section 8.11.2) from Day 1 through EoS. 
• AESIs (Section 8.11.5) from Day 1 through EoS. 
• Assessments for SARS-CoV-2 infection from Day 1 through EoS (Section 8.9.3.1). 
8.10.1. 
Safety Telephone Calls 
A safety telephone call is a telephone call made to the participants’ parent(s)/LAR(s) by trained 
study site personnel. This call will follow a script, which will facilitate the collection of relevant 

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safety information. Safety telephone calls follow a schedule for each participant as indicated in 
the SoA (Table 1). The participants’ parent(s)/LAR(s) will be interviewed according to the script 
and SoA about the occurrence of AEs, MAAEs, SAEs, AESIs, AEs leading to study withdrawal, 
concomitant medications associated with those events, and any nonstudy vaccinations 
(Section 8.11.6). 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’s parent(s)/LAR(s) and 
not documented on the script used for the safety telephone contact. As noted in Section 8.10.2, 
an unscheduled follow-up safety telephone call may be triggered if an eDiary record results in 
identification of a relevant safety event. 
8.10.2. 
Use of Electronic Diaries 
At the time of consent, participants’ parent(s)/LAR(s) 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’ 
parent(s)/LAR(s) will be instructed to download the eDiary application or will be provided an 
eDiary device to record solicited ARs (Section 8.11.3) on Day 1. Based on availability, 
smartphone devices may be provided to those participants’ parent(s)/LAR(s) who do not have 
their own device to use for eDiary activities. 
At each injection visit, participants’ parent(s)/LAR(s) will be instructed (Day 1) or reminded 
(Day 57) on thermometer (axillary and rectal) usage to measure body temperature, ruler usage to 
measure injection site erythema and swelling/induration (hardness), and assessment for localized 
axillary swelling or tenderness on the same side as the injection arm/thigh. 
At each injection visit, participants’ parent(s)/LAR(s) will record data into the eDiary starting 
approximately 30 minutes after injection under the supervision of the study site staff to ensure 
successful entry of assessments. The study site staff will perform any retraining as necessary. 
Participants’ parent(s)/LAR(s) 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’ parent(s)/LAR(s) will record the following data in the eDiary: 
• Solicited local and systemic reactogenicity ARs, as defined in Section 8.11.3, 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). Capturing details of ARs 
in the eDiary should not exceed 7 days after each vaccination. If a solicited local or 

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systemic AR continues beyond Day 7 after vaccination, the event should be reviewed by 
the study site staff either via a telemedicine visit/call or at an unscheduled study site visit. 
• 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. 
Body temperature must be measured via the axillary route and any axillary reading of 
≥ 37.8°C/≥ 100°F may be confirmed by a rectal measurement. 
• 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 document allowed for solicited systemic or local ARs 
(including body temperature measurements). Participants’ parent(s)/LAR(s) will be instructed to 
complete eDiary entries daily. Quantitative temperature 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. 
Study site staff will review eDiary data with participants’ parent(s)/LAR(s) at telemedicine visits 
7 days after each injection in both Part 1 and Part 2. eDiary data will also be reviewed during the 
additional visits 3 days after each injection (ie, on Day 4 and Day 60) in Part 1 only. 
The eDiary will be used every 4 weeks, starting at Day 99 through Day 211 and every 8 weeks, 
starting at Day 265 through Day 377, to capture the occurrence of AEs, MAAEs, SAEs, AESIs, 
or AEs leading to withdrawal. As specified in the SoA (Table 1), the eDiary will prompt the 
participant’s parent(s)/LAR(s) 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 
• Any MAAEs, AESIs, or SAEs 
• Known close contact with someone in the household who has known COVID-19 or 
SARS-CoV-2 infection. An infected person can spread SARS-CoV-2 starting 2 days 
before they have any symptoms (or, for asymptomatic people, 2 days before the positive 
specimen collection date) through 10 days after symptom onset (or, for asymptomatic 

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people, 10 days after positive test). Per the CDC, “close contact” to someone with 
COVID-19 is defined as follows: 
o Being within 6 feet for a total of 15 minutes or more 
o Providing care at home 
o Having direct physical contact (hugged or kissed them) 
o Sharing eating or drinking utensils 
o Being sneezed or coughed upon or getting respiratory droplets on the participant 
• Any experience of symptoms of COVID-19 
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 telemedicine visit or telephone call will be 
triggered which may in turn lead to an unscheduled clinic visit for an assessment as per the 
discretion of the investigator. 
Completion of eDiary questionnaires will alternate with safety telephone calls (Section 8.10.1) as 
the procedure for safety follow-up. These safety telephone calls will take place every 4 weeks 
from Day 113 through Day 225, and every 8 weeks from Day 293 through Day 405 (Table 1). 
8.10.3. 
Blood Sampling Volumes 
The maximum amount of blood collected from each participant over the duration of the study, 
including any extra assessments that may be required, will not exceed blood limits specified by 
local regulations. Repeat or unscheduled samples may be taken for safety reasons or for technical 
issues with the samples. Further details are provided in both the ICF and Laboratory Reference 
Manual. 
8.10.4. 
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. 
8.10.5. 
Ancillary Supplies for Participant Use 
Study sites will distribute Sponsor-provided axillary and rectal thermometers and rulers for use 
by participants’ parent(s)/LAR(s) 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’ parent(s)/LAR(s) who do not have their own device to use for eDiary 
activities. 

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8.11. 
Safety Definitions and Related Procedures 
8.11.1. 
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. 
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). 
• Planned procedures (eg, tonsillectomy or pressure-equalization tubes) that occur during 
the study period but were planned prior to enrollment will not be considered AEs unless 
complications arise. 
An AR is any AE for which there is a reasonable possibility that the vaccine caused the AE 
(Section 8.11.8). 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’ parent(s)/LAR(s) 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, the day of each injection and 
6 subsequent days after injection). 
8.11.2. 
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 

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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 1 overnight stay for 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 AEs; however, if a complication/AE prolongs hospitalization or 
otherwise fulfills SAE criteria, the complication/AE will be recorded as a separate SAE. 
Note: 24-hour observation admissions, typically used to extend the period of observation 
from an emergency department or urgent care visit, will not be considered inpatient 
hospitalization unless they are converted to hospital admission after the 24 hours of 
observation have expired.  
• 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) that 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 that 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. 

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8.11.3. 
Solicited Adverse Reactions 
The term “reactogenicity” refers to the occurrence and intensity of selected signs and symptoms 
(ARs) that occur after IP injection. The eDiary will solicit daily participant reporting of ARs 
using a structured checklist (Section 8.10.2). Participant’s parent(s)/LAR(s) will record such 
occurrences in an eDiary on the day of each dose of injection and for the 6 days after the day of 
dosing. 
Severity grading of reactogenicity will occur automatically based on participant entry into the 
eDiary according to the grading scales presented in Table 7, modified from the Toxicity Grading 
Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventative Vaccine Clinical 
Trials (DHHS 2007). 
Capturing details of ARs in the eDiary should not exceed 7 days after each vaccination. If a 
solicited local or systemic AR continues beyond Day 7 after vaccination, the event should be 
reviewed by the study site staff either via a telephone call or an unscheduled study site visit. All 
solicited ARs (local and systemic) will be considered related to the IP. If a participant’s 
parent(s)/LAR(s) reported a solicited AR during the solicited period and did not record the event 
in the eDiary, the event should be recorded on the Reactogenicity page of the eCRF. If the event 
starts during the solicited period, but continues beyond 7 days after dosing, the participant’s 
parent(s)/LAR(s) should notify the site to provide an end date to close out the event on the 
Reactogenicity page of the eCRF. If the participant’s parent(s)/LAR(s) reported an event after 
the solicited period (ie, after Day 7), it should be recorded as an AE on the AE page of the eCRF. 
Table 7: Solicited Adverse Reactions and Grades: Age 12 Weeks to < 6 Months 
Reaction 
Grade 0 
Grade 1 
Grade 2 
Grade 3 
Grade 41 
Local Reaction 
Injection site 
pain/tenderness 
None 
Mild discomfort 
to touch or some 
pain but no 
interference with 
normal daily 
activities 
Cries when limb is 
moved/refuses to 
move limb or pain 
interferes with 
normal daily 
activities 
Significant 
pain at rest or 
pain prevents 
normal daily 
activities 
Requires 
emergency 
room visit2 or 
hospitalization 
Injection site 
erythema (redness) 
< 5 mm/ 
< 0.5 cm 
5-20 mm/ 
0.5-2.0 cm 
> 20-50 mm 
> 2.0-5.0 cm 
> 50 mm/ 
> 5 cm 
Necrosis or 
exfoliative 
dermatitis 
Injection site 
swelling/induration 
(hardness) 
< 5 mm/ 
< 0.5 cm 
5-20 mm/ 
0.5-2.0 cm 
> 20-50 mm 
> 2.0-5.0 cm 
> 50 mm/ 
> 5 cm 
Necrosis 

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Reaction 
Grade 0 
Grade 1 
Grade 2 
Grade 3 
Grade 41 
Groin or underarm 
swelling or 
tenderness 
ipsilateral to the 
side of injection 
None 
Some swelling 
or tenderness but 
no interference 
with normal 
daily activities 
Swelling or 
tenderness that 
interferes with 
normal daily 
activities 
Swelling or 
tenderness that 
prevents 
normal daily 
activities 
Emergency 
room visit2 or 
hospitalization 
Systemic Reaction 
Fever 
< 38.0°C 
38.0-38.4°C 
100.4-101.1°F 
38.5-39.5°C 
101.2‑103.1°F 
39.6-40.0°C 
103.2-104.0°F 
> 40.0°C 
> 104.0°F 
Irritability/crying 
None 
Lasting < 1 hour 
or easily 
consolable 
Lasting 1 to 
3 hours or 
requiring increased 
attention 
Lasting 
> 3 hours or 
inconsolable 
Requires 
emergency 
room visit2 or 
hospitalization 
Sleepiness 
None 
Sleepier than 
usual or less 
interested in 
surroundings 
Not interested in 
surroundings or 
sleeps through 
meals 
Sleeps most of 
the time, hard 
to arouse 
Inability to 
arouse 
Loss of appetite 
None 
Eating less than 
normal for 
1-2 feeds/meals 
Missed 1-2 feeds/ 
meals completely 
Missed 
> 2 feeds/meals 
completely or 
refuses most 
feeds/meals 
Requires 
emergency 
room visit2 or 
hospitalization 
Abbreviations: AE = adverse event; eCRF = electronic case report form. 
Note: Events listed above but starting > 7 days post-study injection will be recorded on the AE page of the eCRF. 
Causality for each event will be determined per assessment by the investigator. 
1. Grading for Grade 4 events per investigator assessment (with exception of fever). 
2. Emergency room visit includes urgent care visit. 
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 an 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 

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• 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 
8.11.4. 
Medically Attended Adverse Events 
An 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 result follow-up, 
COVID-19 [Section 8.9.2]) 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 8.9.2) will be recorded as MAAEs. Any 
severe COVID-19 cases 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 8.11.10). The investigator will submit any updated COVID-19 case data to the Sponsor 
within 24 hours of it being available. 
All suspected cases of anaphylaxis associated with study drug administration should be recorded 
as MAAEs and reported as an AESI and SAE, 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 8.11.10. 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 described below should be reported as a potential 
case of anaphylaxis. This is 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 
• Involves 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 

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− 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 
8.11.5. 
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 11.2, Appendix 2 for a list of AESIs pertinent to this study. All AESIs will be collected 
through 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 8.11.10). 
8.11.5.1. Acute Myocarditis and/or Pericarditis 
The CDC have established diagnostic criteria for probable or confirmed myocarditis, pericarditis, 
or myopericarditis. The CDC Working Case Definitions are provided in Section 11.3 as 
guidance. In addition to probable or confirmed cases, cases of suspected myocarditis, 
pericarditis, or myopericarditis should be reported as AESIs, even if all of the criteria per the 
CDC Working Case Definitions are not met. Events should also be reported as SAEs if 
seriousness criteria are met (Section 8.11.10). 
An independent CEAC will be utilized and is described in Section 8.12.3. 
8.11.5.2. MISC-C 
MIS-C Case Definition 
Investigators will also be asked to report, as an AESI, clinical signs/symptoms consistent with 
the CDC case definition of MIS-C (CDC 2020b): 

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• An individual aged < 21 years presenting with fever (fever ≥ 38.0°C/≥ 100.4ºF for 
≥ 24 hours, or report of subjective fever lasting ≥ 24 hours), laboratory evidence of 
inflammation (including, but not limited to, one or more of the following: an elevated 
C-reactive protein, erythrocyte sedimentation rate, fibrinogen, procalcitonin, D-dimer, 
ferritin, lactic acid dehydrogenase, or interleukin 6; elevated neutrophils; reduced 
lymphocytes; or low albumin), 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; AND 
• Positive for current or recent SARS-CoV-2 infection by RT-PCR, serology 
(non-S protein-based), or antigen test or COVID-19 exposure within the 4 weeks prior to 
the onset of symptoms. 
Some participants may fulfill full or partial criteria for Kawasaki disease but it 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. 
8.11.6. 
Recording and Follow-up of an AE and/or SAE 
The investigator is responsible for ensuring that all AEs and SAEs are recorded in the eCRF and 
reported to the Sponsor. 
Solicited ARs will be collected during the 7 days following each injection (ie, the day of 
injection and 6 subsequent days). Other (unsolicited) AEs will be collected during the 28 days 
following each injection (ie, the day of injection and 27 subsequent days). 
Both MAAEs and SAEs will be collected from participants as specified in the SoA (Table 1) 
until the end of their participation in the study. Any AEs that occur before administration of IP 
will be analyzed separately from AEs that occur after vaccine administration. 
At every study site visit or telephone contact, participant’s parent(s)/LAR(s) will be asked a 
standard question to elicit any medically-related changes in the participant’s well-being 
(including COVID-19 symptoms). Participant’s parent(s)/LAR(s) will also be asked if the 
participant has 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. 

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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 7.5). 
8.11.7. 
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 8.11.2), 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), modified for use in infants 
12 weeks to < 6 months of age (Table 7), will be used to categorize local and systemic 
reactogenicity events (solicited ARs) and body temperature measurements observed during this 
study. Specific criteria for local and systemic reactogenicity events are presented in 
Section 8.11.3. 
The determination of severity for all unsolicited AEs should be made by the investigator based 
upon medical judgment and the definitions 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’s parent(s)/LAR(s) the impact of AEs on the 
participant’s activities of daily living to assess severity and document it 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 the 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. 
8.11.8. 
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. 

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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 classifications: 
Not related: There is not a reasonable possibility of a relationship to the IP. Participant did not 
receive the IP OR the temporal sequence of AE onset relative to administration of the IP is not 
reasonable OR the AE is more likely explained by a cause other 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 AE onset relative to the administration of the IP is 
reasonable. The AE is more likely explained by the IP than by another cause. 
8.11.9. 
Reporting Adverse Events 
The investigator is responsible for reporting all AEs that are observed or reported at the times 
specified in the SoA (Table 1), 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 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, any required treatments 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, including ongoing SAEs after study completion. 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. 
8.11.10. 
Reporting SAEs 
Prompt notification by the investigator to the Sponsor of an SAE is essential so that legal 
obligations and ethical responsibilities towards 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 8.11.2) 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 

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of any SAE as outlined in the 21 US CFR Parts 312 and 320. The investigator is responsible for 
notifying the IRB directly. 
If the eCRF is unavailable at the time of the SAE, the paper SAE/AESI report form distributed to 
the study sites should be completed and sent via e-mail or fax as provided on the forms. 
Regulatory reporting requirements for SAEs are described in Section 8.11.14. 
The investigator and any qualified designees are responsible for detecting, documenting, and 
recording events that meet the definition of an AE, including SAEs and AESIs, 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. 
8.11.11. 
Time Period and Frequency for Collecting AE, AESI, MAAE, and SAE 
Information 
Medical occurrences that begin before the start of IP dosing but after obtaining informed 
consent/assent 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’s parent(s)/LAR(s) 
• Questioning the participant’s parent(s)/LAR(s) 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, AESIs, and MAAEs will be collected from the start of IP dosing until the last day 
of study participation at the time points specified in the SoA (Table 1). 
All SAEs and AESIs will be recorded and 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 SAE or AESI from a study participant or receives updated data on 
a previously reported SAE or AESI and the eCRF has been taken offline, then the site can report 
this information on a paper SAE or AESI form using the SAE Mailbox, the SAE Hotline, or the 
SAE Fax line (Section 8.11.10).  
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, or is considered an AESI). If this is the 

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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 conclusion of the study 
participation (EoS). However, if an investigator learns of any SAE, including a death, at any time 
after a participant has completed or withdrawn from the study, and considers the event to be 
reasonably related to the study IP or study participation, the investigator must promptly notify 
the Sponsor. 
8.11.12. 
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. 
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’s parent(s)/LAR(s) is the preferred method to 
inquire about the occurrence of AEs. 
8.11.13. 
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, AESIs, MAAEs, 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 7.5. 
8.11.14. 
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 towards the safety of participants and the safety of 
a study intervention under clinical investigation are met. 

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• 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 ARs 
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. 
8.12. 
Safety Oversight 
Safety monitoring for this study will include the blinded study team members, inclusive of at a 
minimum, the Sponsor medical monitor and CRO’s medical monitor, as well as safety reviews 
by an unblinded DSMB. The study team will conduct ongoing blinded safety reviews during the 
study and will be responsible for notifying the DSMB of potential safety signals. 
8.12.1. 
Internal Safety Team 
An IST will review safety data throughout the study. Further details of IST review are described 
in the overall study design Section 4.1. In addition, the IST will escalate any safety concerns to 
the DSMB. The frequency of IST meetings will be described in more detail in the IST charter. 
8.12.2. 
Data Safety Monitoring Board 
The DSMB, composed of external, independent subject matter experts, including an unblinded 
statistician, will conduct unblinded reviews of safety data on a periodic basis, as defined in a 
DSMB charter, or as otherwise requested by the study team. 
Members of the DSMB will be independent from study conduct and free of conflict of interest. 
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. 
If any of the study pause rules as described in Section 7.4 are met, the Sponsor will immediately 
suspend further enrollment and/or study dosing and the DSMB will convene on an ad hoc basis. 
The DSMB will review all available unblinded study data (as applicable) to help adjudicate any 
potential study pauses and make recommendations on further study conduct, including 
requesting additional information, recommending stopping the study, recommending changes to 

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study conduct and/or the protocol, or recommending additional operational considerations due to 
safety issues that arise during the study. 
8.12.3. 
Cardiac Event Adjudication Committee 
An independent CEAC that includes pediatric cardiologists will review suspected cases of 
myocarditis and/or pericarditis to determine if they meet CDC criteria of “probable” or 
“confirmed” events, assess severity (Gargano et al 2021), and make recommendations in 
consultation with the DSMB, if necessary, to the Sponsor. Any cases that the CEAC assesses as 
representing probable or confirmed cases of myocarditis and/or pericarditis will be referred to 
the Sponsor, who will then make a final decision on whether to suspend further enrollment 
and/or study dosing based on an assessment of the overall potential risk to study participants. 
The CEAC will operate under the rules of an approved charter. Details regarding the CEAC 
composition, responsibilities, procedures, and frequency of data review will be defined in its 
charter. 
8.13. 
Treatment of Overdose 
As the study treatment is to be administered by an HCP, it is unlikely that an overdose will 
occur. Dose deviations will be tracked as protocol deviations (Section 11.1.8). 
8.14. 
Pharmacokinetics 
Pharmacokinetic parameters will not be evaluated in this study. 
8.15. 
Pharmacodynamics 
Pharmacodynamic parameters will not be evaluated in this study. 
8.16. 
Biomarkers 
Immunogenicity assessments are presented in Section 8.8. Biomarkers will not be evaluated in 
this study. 

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9. 
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. 
9.1. 
Blinding and Responsibility for Analyses 
Part 1 of this study will be open-label, blinding procedures will not be applicable. 
Part 2 of this study will be conducted in an observer-blind manner. The investigator, study staff, 
study participant’s parent(s)/LAR(s), study site monitors, and Sponsor personnel (or its 
designees) will be blinded to the IP administered until study end, with the following exceptions: 
• Unblinded pharmacy personnel (of limited number) responsible for vaccine management, 
documentation, accountability, preparation, and administration (Section 6.2). 
• 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 independent unblinded statistical and programming team who are not involved in the 
design and conduct of the study will perform the primary analyses in Part 2 
(Section 9.6.2). Selected Sponsor team members including biostatistician and statistical 
programmers will be pre-specified to be unblinded to the primary analysis results and 
will not communicate the results of primary analysis to the blinded investigators, study 
site staff, clinical monitors, or participants. The details will be included in the Data 
Blinding Plan. 
• The DSMB may review data, as appropriate, to safeguard the interests of clinical study 
participants and to help ensure the integrity of the study. 
The planned study analyses are described in Section 9.6. Procedures for breaking the blind in the 
case of a medical emergency are provided in Section 6.3.8. 

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9.2. 
Statistical Hypotheses 
Part 1: 
There is no statistical hypothesis to be tested in Part 1. 
Part 2: 
Primary Hypotheses: 
1) HA1: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months is 
noninferior to the primary series of 100 µg mRNA-1273 in adults based on GMR against 
the VOC (Omicron) with a noninferiority margin of 1.5-fold (lower bound of CI for 
GMR > 0.67). 
2) HA2: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months is 
noninferior to the primary series of 100 µg mRNA-1273 in adults based on difference in 
SRR against the VOC (Omicron) with a noninferiority margin of < 5% (lower bound of 
CI for SRR > –5%). 
Secondary Hypotheses: 
3) HA3: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months is 
superior to the primary series of 100 µg mRNA-1273 in adults based on GMR against the 
VOC (Omicron) with a superiority margin of > 1-fold (lower bound of CI for GMR > 1). 
4) HA4: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months is 
superior to the primary series of 100 µg mRNA-1273 in adults based on difference in 
SRR against the VOC (Omicron) with a superiority margin of > 0% (lower bound of CI 
for SRR > 0%). 
5) HA5: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months is 
“super” superior to the primary series of 100 µg mRNA-1273 in adults based on GMR 
against the VOC (Omicron) with a “super” superiority margin of > 1.5-fold (lower bound 
of CI for GMR > 1.5). 
6) HA6: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months is 
“super” superior to the primary series of 100 µg mRNA-1273 in adults based on 
difference in SRR against the VOC (Omicron) with a “super” superiority margin of 
> 10% (lower bound of CI for SRR > 10%). 
7) HA7: The immune response of mRNA-1273.214 against the VOC (Omicron) in 
participants 12 weeks to < 6 months is noninferior to the primary series of 100 µg 
mRNA-1273 against the SARS-CoV-2 original strain in adults, based on GMR with a 
noninferiority margin of 1.5-fold (lower bound of CI for GMR > 0.67). 

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8) HA8: The immune response of mRNA-1273.214 against the VOC (Omicron) in 
participants 12 weeks to < 6 months is noninferior to the primary series of 100 µg 
mRNA-1273 against the SARS-CoV-2 original strain in adults, based on difference in 
SRR with a noninferiority margin of < 5% (lower bound of CI for SRR > –5%). 
9) HA9: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months is 
noninferior to the primary series of 100 µg mRNA-1273 in adults based on GMR against 
the SARS-CoV-2 original strain with a noninferiority margin of 1.5-fold (lower bound of 
CI for GMR > 0.67). 
10) HA10: The immune response of mRNA-1273.214 in participants 12 weeks to < 6 months 
is noninferior to the primary series of 100 µg mRNA-1273 against the original strain in 
adults based on difference in SRR against the SARS-CoV-2 original strain with a 
noninferiority margin of < 5% (lower bound of CI for SRR > –5%). 
9.3. 
Sample Size and Power Calculation 
In Part 2, approximately 600 infant participants 12 weeks to < 6 months of age will be enrolled at 
the dose level selected for Part 2, with an mRNA-1273.214 to placebo ratio of 1:1. Assuming 
10% to 15% participants are not negative SARS-CoV-2 status at baseline, it is estimated that 
there will be a minimum of approximately 250 evaluable participants in the mRNA-1273.214 
arm eligible for immunogenicity analyses.  
The sample size of approximately 300 infant participants in the mRNA-1273.214 arm in Part 2 is 
considered to be sufficient to support a safety assessment. There is at least 90% probability to 
observe at least 1 participant with an AE at a true AE rate of 1% in this group.  
The sample size calculation for each of the 2 primary noninferiority hypothesis tests (HA1 and 
HA2) was performed, and the larger sample size was chosen for the study. 
• With approximately 250 evaluable participants receiving mRNA-1273.214 in the 
PPIS-Neg in Study mRNA-1273-P206 and adults (≥ 18 years of age) in 
Study mRNA-1273-P301, there will be at least 90% power to demonstrate noninferiority 
of the immune response against Omicron variant, as measured by the GMT, in infant 
population at a 2‑sided alpha of 0.05, compared with that in adults (≥ 18 years of age) in 
Study mRNA-1273-P301 receiving mRNA‑1273, assuming an underlying GMR (which 
is calculated as ratio of GMT) value of 1 and the standard deviation of the natural 
log-transformed titer is assumed to be 1.0, and a noninferiority margin of > 0.67. 
• With approximately 250 evaluable participants receiving mRNA-1273.214 in the 
PPIS-Neg in Study mRNA-1273-P206 and adults (≥ 18 years of age) in 
Study mRNA-1273-P301, there will be at least 90% power to demonstrate noninferiority 

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of the immune response against Omicron variant as measured by SRR in infants at a 
2-sided alpha of 0.05, compared with SRR against Omicron variant in adults ≥ 18 years 
of age in Study mRNA-1273-P301 receiving mRNA-1273, assuming SRR of 60% to 
70% in Study mRNA-1273-P301, true SRR improvement of 10% in infants from 
Study mRNA-1273-P206 compared with adults from Study mRNA-1273-P301, and a 
noninferiority margin of 5%.  
9.4. 
Analysis Populations 
The analysis populations are defined in Table 8. 
Table 8: Populations for Analyses 
Analysis Set 
Description 
Randomization Set 
All participants who are randomly assigned in Part 2, regardless of 
the participants’ treatment status in the study. 
FAS 
Part 1: All enrolled participants in Part 1 who receive at least 1 dose 
of mRNA-1273.214. 
Part 2: All randomized participants in Part 2 who receive at least 
1 dose of IP. 
mITT Set 
All participants in the FAS who have no serologic or virologic 
evidence of prior SARS-CoV-2 infection at baseline (ie, both 
negative RT-PCR test for SARS-CoV-2 and negative serology test 
based on bAb specific to SARS-CoV-2 nucleocapsid). 
mITT-1 Set 
All participants in the mITT Set excluding those who received the 
wrong treatment (ie, at least 1 dose received that is not as 
randomized).  
PP Set 
All participants in the FAS who receive planned doses of IP per 
schedule and are SARS-CoV-2 negative at baseline (ie, both 
negative RT-PCR test for SARS-CoV-2 and negative serology test) 
and have no major protocol deviations that impact key or critical 
data. 
Immunogenicity Set 
All participants in the FAS who provide immunogenicity samples. 
PPIS 
Participants in the Immunogenicity Set who receive planned doses 
of IP per schedule, comply with immunogenicity testing schedule, 
and have no major protocol deviations that impact key or critical 
data. The PPIS will be used for analyses of immunogenicity. 

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Analysis Set 
Description 
PPIS-Neg 
Participants in the PPIS who have no serologic or virologic evidence 
of SARS-CoV-2 infection at baseline (ie, both negative RT-PCR test 
for SARS-CoV-2 and negative serology test). The PPIS-Neg will be 
the primary analysis set for analyses of immunogenicity. 
Safety Set 
All enrolled participants in Part 1 and all randomly assigned 
participants in Part 2 who receive at least 1 dose of IP. The Safety 
Set will be used for all analyses of safety except for solicited ARs.  
Solicited Safety Set 
All participants in the Safety Set who contribute any solicited AR 
data. The Solicited Safety Set will be used for the analyses of 
solicited ARs.  
Abbreviations: AR = adverse reaction; bAb = binding antibody; FAS = full analysis set; IP = investigational 
product; mITT = modified intent to treat; mRNA = messenger RNA; PP = per protocol; PPIS = Per-Protocol 
Immunogenicity Set; PPIS-Neg = Per-Protocol Immunogenicity Set – SARS-CoV-2 Negative; RT-PCR = reverse 
transcriptase polymerase chain reaction; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2. 
9.5. 
Statistical Analyses 
9.5.1. 
Immunogenicity Analyses 
The primary analysis population for immunogenicity will be the PPIS-Neg, unless specified 
otherwise. The primary objective of Part 2 of this study is to use the immunogenicity response to 
infer effectiveness of mRNA-1273.214 vaccine administered as 2 doses 8 weeks apart in infants 
aged 12 weeks to < 6 months at the dose level selected for investigation.  
Immunogenicity Analyses for mRNA-1273.214 Primary Series 
Immune response as measured by GMT value and SRR in the infant group based on Ab levels 
will be compared to that in adult (≥ 18 years of age) participants from Study mRNA-1273-P301 
using Ab data. The immunogenicity data from participants who are assigned to the same dose 
level in Part 1 and Part 2 of this study may be combined for the immunogenicity analyses. 
To assess the difference in immune response between the infant participants in 
Study mRNA-1273-P206 at 28 days after the last dose of mRNA-1273 primary series compared 
to the adult (≥ 18 years of age) participants in Study mRNA-1273-P301 at Day 57, an analysis of 
covariance model will be carried out with Ab as dependent variable and a group variable (an 
mRNA-1273 arm/group of Study mRNA-1273-P206 versus participants in 
Study mRNA-1273-P301) as the fixed variable for each participant arm/group, the analysis may 
adjust for key characteristics such as age, sex, etc. The GMT value of mRNA-1273.214 arm at 
28 days after the last dose of mRNA-1273.214 primary series and GMT value of mRNA-1273 at 
Day 57 (28 days after the second dose of primary series) in Study mRNA-1273-P301 will be 

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estimated by the GLSM from the model. The GMR (which is calculated as ratio of GMT) will be 
estimated by the ratio of GLSM from the model. The corresponding 2-sided 95% CI of GMR 
will also be provided.  
The noninferiority of GMT of mRNA-1273.214 primary series compared with mRNA-1273 
primary series will be considered demonstrated if: 
• The lower bound of the 95% CI of the GMR (the infant participants in 
Study mRNA-1273-P206 at 28 days after the last dose of mRNA-1273.214 primary 
series, compared with the participants in Study mRNA-1273-P301 at Day 57) > 0.67 
based on the noninferiority margin of 1.5.  
In addition, the GMT of antibodies with corresponding 95% CI will be provided at each time 
point. The 95% CIs will be calculated based on the t-distribution of the log-transformed titer 
values then back transformed to the original scale. Descriptive summary statistics for GMT 
including median, minimum, and maximum will also be provided. 
The GM fold rise of specific antibodies with corresponding 95% CI at each post-baseline time 
point over pre-Dose 1 baseline at Day 1 will be provided. The 95% CIs will be calculated based 
on the t-distribution of the log-transformed values then back transformed to the original scale for 
presentation.  
The number and percentage of participants with seroresponse due to vaccination will be provided 
with 2-sided 95% CI using the Clopper-Pearson method at each post-baseline time point with 
Day 28 after the last dose of mRNA-1273.214 primary series being of the primary interest in the 
analyses, where seroresponse is defined as a titer change from baseline (pre-Dose 1) below the 
LLOQ to ≥ 4 × LLOQ, or at least a 4-fold rise if baseline is ≥ LLOQ. 
The SRR difference with 95% CI (using Miettinen-Nurminen score method) between infants 
receiving mRNA-1273.214 primary series in Study mRNA-1273-P206 at 28 days after the last 
dose of mRNA-1273.214 primary series and adult participants receiving mRNA-1273 primary 
series in Study mRNA-1273-P301 at Day 57 will be provided.  
The noninferiority of seroresponse of mRNA-1273.214 primary series in 
Study mRNA-1273-P206 compared with mRNA-1273 primary series in 
Study mRNA-1273-P301 will be considered demonstrated if: 
• The lower bound of the 95% CI of the SRR difference is > –5% based on the 
noninferiority margin of 5%. 

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Hypothesis Testing Strategy for Immunogenicity: 
The hypothesis tests for noninferiority, superiority, and “super” superiority of mRNA-1273.214 
against Omicron as compared to mRNA-1273 primary series against Omicron will be performed 
sequentially. The noninferiority hypotheses (hypotheses HA1 and HA2) will be tested first. 
Once noninferiority is demonstrated based on both GMT and SRR, superiority (hypotheses HA3 
and HA4) of mRNA-1273.214 as compared to mRNA-1273 primary series will be tested. If the 
lower bound of the 95% CI of the GMR is > 1, superiority based on GMT is demonstrated; if the 
lower bound of the 95% CI of the SRR difference is > 0%, superiority based on seroresponse is 
demonstrated. 
Once superiority is demonstrated based on both GMT and SRR, “super” superiority (hypotheses 
HA5 and HA6) of mRNA-1273.214 as compared to mRNA-1273 primary series will be tested. If 
the lower bound of the 95% CI of the GMR is > 1.5, “super” superiority based on GMT is 
demonstrated; if the lower bound of the 95% CI of the SRR difference is > 10%, “super” 
superiority based on seroresponse is demonstrated. 
9.5.2. 
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 vaccination 
group (dose levels of mRNA-1273.214 and placebo).  
Safety and reactogenicity will be assessed by clinical review of all relevant parameters including 
solicited ARs (local and systemic events), unsolicited AEs, SAEs, MAAEs, AESIs, and AEs 
leading to discontinuation from IP and/or study participation.  
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 
by toxicity grade 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, severe 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. 
Solicited AR events (starting within 7 days after any injection) that are serious or lasting beyond 
Day 7 after any injection will also be reported as unsolicited AEs. 
The number of events of solicited ARs, unsolicited AEs/SAEs, MAAEs, severe AEs, and AEs 
leading to discontinuation from IP or withdrawal from the study will be reported in summary 
tables accordingly. 

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For all other safety parameters, descriptive summary statistics will be provided, and Table 9 
summarizes the analysis strategy for safety endpoints. Further details will be described in the 
SAP. 
Table 9: 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 unsolicited MAAE 
X 
– 
Any unsolicited treatment-related AE 
X 
– 
Any treatment-related SAE 
X 
– 
Discontinuation due to AE 
X 
– 
Any severe AE 
X 
– 
Any treatment-related severe AE 
X 
– 
Any AESI 
X 
– 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; 
CI = confidence interval; MAAE = medically attended adverse event; MedDRA = Medical Dictionary for 
Regulatory Activities; PT = preferred term; SAE = serious adverse event; SOC = system organ class. 
Note: 95% CI using the Clopper-Pearson method. X = results will be provided. Solicited ARs and unsolicited AEs 
will be summarized by SOC and PT coded by MedDRA. 
9.5.3. 
Exploratory Analyses 
The exploratory analyses of the effectiveness of mRNA-1273.214 will evaluate the incidence of 
COVID-19, SARS-CoV-2 infection regardless of symptomatology or severity, severe 
COVID-19, etc. 
To evaluate the incidence of COVID-19 after vaccination with mRNA-1273.214 or placebo, the 
incidence rate will be provided by vaccination group, calculated as the number of cases divided 
by the total person-time. 
For serologically confirmed SARS-CoV-2 infection or COVID-19, regardless of 
symptomatology or severity, infection rate will be provided by vaccination group. The same 
analysis will be performed for asymptomatic SARS-CoV-2 infection. 

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The exploratory analyses of the effectiveness will be performed primarily on the PP Set, unless 
specified otherwise. Sensitivity analyses for effectiveness will be performed on other select 
analysis sets, eg, mITT and/or mITT-1.  
For the exploratory analyses for mRNA-1273.214 against other variants of interests, the same 
analyses methods described in Section 9.5.1 will be employed to analyze immunogenicity data. 
More details of exploratory analyses will be described in the SAP before database lock. 
9.5.4. 
Subgroup Analyses 
Subgroup analyses will be performed in select subgroups including but not limited to the 
following subgroups: 
• Sex (male, female) 
• SARS-CoV-2 status at baseline  
• Maternal immunization status  
• Race 
• Ethnicity 
Details of subgroups analyses will be provided in the SAP. 
9.6. 
Planned Analyses 
9.6.1. 
Interim Analyses 
• For Part 1, interim analyses of safety and immunogenicity will be performed after all 
treated participants in one or both arms have completed 28 days after the last dose of the 
primary series of mRNA-1273.214.  
•  For Part 2, an interim analysis of safety and immunogenicity will be performed after all 
participants have completed 28 days after the last dose of the primary series of 
mRNA-1273.214. This interim analysis will be considered the primary analysis for 
immunogenicity.  
9.6.2. 
Final Analysis 
The final analysis of all endpoints will be performed after 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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2022;327(11):1087-9. 
Topjian AA, Raymond TT, Atkins D, Chan M, Duff JP, Joyner BL Jr, et al; and Pediatric Basic 
and Advanced Life Support Collaborators. Part 4: Pediatric basic and advanced life support: 
2020 American Heart Association Guidelines for cardiopulmonary resuscitation and emergency 
cardiovascular care. Circulation. 2020;142(16_suppl_2):S469-S523. 
Tseng HF, Ackerson BK, Luo Y, Sy LS, Talarico CA, Tian Y, et al. Effectiveness of 
mRNA-1273 against SARS-CoV-2 Omicron and Delta variants. Nat Med. 2022;28(5):1063-71. 
UNICEF. COVID-19 confirmed cases and deaths. Updated March 2022. Available from: 
https://data.unicef.org/resources/covid-19-confirmed-cases-and-deaths-dashboard/. 
United Kingdom Health Security Agency (UKHSA). SARS-CoV-2 variants of concern and 
variants under investigation in England Technical briefing: Update on hospitalisation and 
vaccine effectiveness for Omicron VOC-21NOV-01 (B.1.1.529). December 2021. Available 
from: 
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file
/1045619/Technical-Briefing-31-Dec-2021-Omicron_severity_update.pdf. 
Verdoni L, Mazza A, Gervasoni A, Martelli L, Ruggeri M, Ciuffreda M, et al. An outbreak of 
severe Kawaski-like disease at the Italian epicentre of the SARS-CoV-2 epidemic: an 
observational cohort study. Lancet. 2020;395(10239):1771-8. 
World Health Organization (WHO). Statement on the second meeting of the International Health 
Regulations (2005) Emergency Committee regarding the outbreak of novel coronavirus (2019-
nCoV) [Internet]. Geneva, Switzerland: WHO; 2020 January 30 [cited 2022 May 04]. Available 

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from: https://www.who.int/news/item/30-01-2020-statement-on-the-second-meeting-of-the-
international-health-regulations-(2005)-emergency-committee-regarding-the-outbreak-of-novel-
coronavirus-(2019-ncov) 
World Health Organization (WHO). WHO Director-General’s opening remarks at the media 
briefing on COVID-19 – 11 March 2020 [Internet]. Geneva, Switzerland: WHO; 2020 March 11 
[cited 2022 May 04]. Available from: https://www.who.int/director-general/speeches/detail/who-
director-general-s-opening-remarks-at-the-media-briefing-on-covid-19---11-march-2020 
Zambrano LD, Newhams MM, Olson SM, Halasa NB, Price AM, Boom JA, et al; and 
Overcoming COVID-19 Investigators. Effectiveness of BNT162b2 (Pfizer-BioNTech) mRNA 
Vaccination Against Multisystem Inflammatory Syndrome in Children Among Persons Aged 
12-18 Years - United States, July-December 2021. MMWR Morb Mortal Wkly Rep. 
2022;71(2):52-8. 
 

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11. 
SUPPORTING DOCUMENTATION AND OPERATIONAL 
CONSIDERATIONS

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11.1. 
APPENDIX 1: Study Governance Considerations 
11.1.1. 
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. 
11.1.2. 
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: 
• 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 

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will be documented in a clinical study agreement between the Sponsor, designated CRO, 
and the investigator. 
According to ICH GCP guideline, 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 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 purposes: 
• 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. 

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11.1.3. 
Audits and Inspections  
The Sponsor, their designee(s), the IRB, or regulatory authorities will be allowed to conduct 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 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 GCP (R2), 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 form and 
recruitment materials must be maintained by the investigator and made available for inspection. 
11.1.4. 
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. 
11.1.5. 
Recruitment Strategy 
Enrollment targets will be established to ensure the participant population reflects those that are 
most at risk for the condition, or those that are most reflective of the general population, if 
appropriate. 
Participant recruitment and retention initiatives will be incorporated into the trial. These include, 
but are not limited to, services that provide a means to identify potential participants and direct 
them to participating clinical trial sites, participant support services such as concierge, and trial 
information and support collateral for both the participant and the site. Advertisements to be 

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used for the recruitment of study participants, and any other written information regarding 
this study to be provided to the participant’s parent(s)/LAR(s) should be submitted to the 
Sponsor for approval. All documents must be approved by the IRB.  
11.1.6. 
Informed Consent Process 
The informed consent document(s) must meet the requirements of 21 CFR 50, local regulations, 
ICH guidelines, Health Insurance Portability and Accountability Act requirements, where 
applicable, and the IRB or study site. All consent documents will be approved by the appropriate 
IRB. The actual ICF used at each 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 parent(s)/LAR(s) 
willingness to continue participation of their child 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’s 
parent(s)/LAR(s) and answer all questions regarding the study. 
The investigator is responsible for ensuring that the participant’s parent(s)/LAR(s) 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’s parent(s)/LAR(s) 
must be informed that participation is voluntary. The participant’s 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’s parent(s)/LAR(s) must be allowed sufficient time to decide whether they wish 
to let their child participate in the study. 
The participant’s parent(s)/LAR(s) must be made aware of, and give consent to, direct access to 
the participant’s source medical records by study monitors, auditors, the IRB, and regulatory 
authorities. The participant’s parent(s)/LAR(s) should be informed that such access will not 
violate participant confidentiality or any applicable regulations. The participant’s 
parent(s)/LAR(s) should also be informed that they are authorizing such access by signing the 
ICF. 

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A copy of the ICF(s) must be provided to the participant’s parent(s)/LAR(s). 
Parent(s)/LAR(s) of a participant who is rescreened (allowed once) are 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. 
11.1.7. 
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. Approval of the IRB 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 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 investigator(s), and notified to the IRB(s). 
11.1.8. 
Protocol Deviations  
The noncompliance may be either on the part of the participant, the investigator, or the study site 
staff. As a result of deviations, corrective actions are to be developed by the site and 
implemented promptly. 
It is the responsibility of the 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 

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study source documents and reported to the 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. 
11.1.9. 
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’s parent(s)/LAR(s) must be informed that the participant’s 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’s parent(s)/LAR(s). 
The participant’s parent(s)/LAR(s) must be informed that the participant’s 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’s parent(s)/LAR(s) will be asked to complete a form allowing the investigator to 
notify the participant’s primary healthcare 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’s parent(s)/LAR(s), 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. 
11.1.10. 
Sample Retention and Future Biomedical Research 
ModernaTX, Inc. may store samples for the time frame specified in the ICF to achieve study 
objectives and to address further scientific questions related to mRNA‑1273.214 or 
anti‑respiratory virus immune response. In addition, identifiable samples can be destroyed at any 

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time at the request of the participant’s parent(s)/LAR(s). 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 and 
samples collected and stored in Part 1 or Part 2. These analyses will extend the search for other 
potentially relevant biomarkers to investigate the effect of mRNA‑1273.214, as well as to 
determine how changes in biomarkers may relate to exposure and clinical outcomes. A decision 
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. 
11.1.11. 
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), etc., 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 ensured. Details on data sharing criteria and the 
process for requesting access can be found at this web address: clinicalstudydatarequest.com. 
11.1.12. 
Data Quality Assurance and Quality Control 
Data collection is the responsibility of the clinical study staff at the site under the supervision of 
the 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. 

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• 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 checks 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 CRF by authorized site personnel are accurate, complete, and 
verifiable from source documents; that the safety and rights of participants are 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 as described in Section 11.1.15. 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.  
11.1.13. 
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.  

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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 
WHODrug Dictionary.  
11.1.14. 
Source Documents 
Source documents are original documents or certified copies, and include, but are not limited to, 
eDiaries, medical and hospital records, screening logs, ICFs, 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 
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. 
11.1.15. 
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. 

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11.1.16. 
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 participant 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 the following: 
• 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-1273.214 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. 
11.1.17. 
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. 

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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. 
 

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11.1.18. 
Height and Weight Chart for Boys and Girls 
For boys from birth to 2 years  
 

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For girls from birth to 2 years  
 

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11.2. 
APPENDIX 2: Adverse Events of Special Interest Terms 
The investigator’s medical judgement must be applied to assess an event as an AESI, as most 
AESIs are based on medical concepts. Table 10 does not provide a comprehensive list of terms.  
Table 10 describes events/medical concepts that are of interest in COVID-19 vaccine safety 
surveillance. Some are specific to vaccines; however, some are of interest due to their occurrence 
in the context of concurrent or recent COVID-19. Events falling into the descriptions below 
(Table 10) should be reported as AESIs, per the reporting processes specified in Section 8.11.5, 
even when they occur during/following COVID infection.  
It should be noted that COVID-19 itself is not an AESI. 
Table 10: Adverse Events of Special Interest 
Medical Concept 
Medical Concept Descriptions/Guidance 
Anosmia, ageusia 
• 
New onset of anosmia or ageusia associated with COVID-19 or 
idiopathic etiology  
• 
DOES NOT INCLUDE anosmia or ageusia associated with 
sinus/nasal congestion, congenital, or traumatic etiologies  
Subacute thyroiditis 
• 
Acute inflammatory disease of the thyroid (immune-mediated or 
idiopathic) 
• 
DOES NOT INCLUDE new onset of chronic thyroiditis 
Acute pancreatitis 
• 
New onset of pancreatitis in the absence of a clear, alternate 
etiology, such as alcohol, gallstones, trauma, recent invasive 
procedure, etc. 
Appendicitis  
• 
Any event of appendicitis  
Rhabdomyolysis 
• 
New onset of rhabdomyolysis in the absence of a clear, alternate 
etiology, such as drug/alcohol abuse, excessive exercise, trauma, 
etc. 
Acute respiratory distress 
syndrome  
• 
New onset of ARDS/respiratory failure due to acute 
inflammatory lung injury 

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Medical Concept 
Medical Concept Descriptions/Guidance 
• 
DOES NOT INCLUDE non-specific symptoms of shortness of 
breath or dyspnea, nor events with underlying etiologies of heart 
failure or fluid overload 
Coagulation disorders 
• 
New onset of thrombosis, thromboembolic event, or 
non-traumatic hemorrhage/bleeding disorder (eg, stroke, DVT, 
pulmonary embolism, DIC, etc) 
Acute cardiovascular injury 
• 
New onset of clinically confirmed, acute cardiovascular injury, 
such as myocarditis, pericarditis, arrhythmia confirmed by ECG 
(eg, atrial fibrillation, atrial flutter, supraventricular 
tachycardia), stress cardiomyopathy, heart failure, acute 
coronary syndrome, myocardial infarction, etc. 
• 
DOES NOT INCLUDE transient sinus tachycardia/bradycardia, 
non-specific symptoms such as palpitations, racing heart, heart 
fluttering or pounding, irregular heartbeats, shortness of breath, 
chest pain/discomfort, etc. 
Acute kidney injury 
• 
New onset of acute kidney injury or acute renal failure in the 
absence of a clear, alternate etiology, such as urinary tract 
infection/urosepsis, trauma, tumor, nephrotoxic 
medications/substances, etc.; 
• 
Increase in serum creatinine by ≥ 0.3 mg/dL (or ≥ 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 
Acute liver injury 
• 
New onset in the absence of a clear, alternate etiology, such as 
trauma, tumor, hepatotoxic medications/substances, etc.; 
• 
> 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 

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Medical Concept 
Medical Concept Descriptions/Guidance 
• 
Single organ cutaneous vasculitis 
• 
Erythema multiforme 
• 
Bullous rash 
• 
Severe cutaneous adverse reactions, such as Stevens-Johnson 
syndrome, toxic epidermal necrolysis, drug reaction with 
eosinophilia and systemic symptoms, fixed drug eruptions, and 
necrotic or exfoliative reactions 
Systemic inflammatory 
syndromes  
• 
MIS-A or MIS-C 
• 
Kawasaki’s disease 
• 
Hemophagocytic lymphohistiocytosis 
Thrombocytopenia 
• 
Platelet count < 150 ×109/L (thrombocytopenia) 
• 
New clinical diagnosis, or worsening, of thrombocytopenic 
condition, such as immune thrombocytopenia, 
thrombocytopenic purpura, or HELLP syndrome 
Acute aseptic arthritis 
• 
Clinical syndrome characterized by acute onset of signs and 
symptoms of joint inflammation without recent trauma for a 
period of no longer than 6 weeks, synovial increased leukocyte 
count and the absence of microorganisms on Gram stain, routine 
culture, and/or PCR 
• 
DOES NOT INCLUDE new onset of chronic arthritic conditions 
New onset, or worsening, 
of neurological disease 
• 
Immune-mediated neurological disorders 
• 
Guillain-Barre syndrome 
• 
Acute disseminated encephalomyelitis 
• 
Peripheral facial nerve palsy (Bell’s palsy)  
• 
Transverse myelitis 
• 
Encephalitis/encephalomyelitis 
• 
Aseptic meningitis 

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Medical Concept 
Medical Concept Descriptions/Guidance 
• 
Seizures/convulsions/epilepsy 
• 
Narcolepsy/hypersomnia 
Anaphylaxis  
• 
Anaphylaxis associated with study drug administration 
Other syndromes 
• 
Fibromyalgia  
• 
Postural orthostatic tachycardia syndrome  
• 
Chronic fatigue syndrome  
• 
Myalgic encephalomyelitis  
• 
Post viral fatigue syndrome 
• 
Myasthenia gravis 
Abbreviations: ALP = alkaline phosphatase; ALT = alanine aminotransferase; ARDS = acute respiratory distress 
syndrome; AST = aspartate aminotransferase; COVID-19 = coronavirus disease 2019; DIC = disseminated 
intravascular coagulation; DVT = deep vein thrombosis; ECG = electrocardiogram; GGT = gamma-glutamyl 
transferase; HELLP = hemolysis, elevated liver enzymes, and low platelets; MIS-A = multisystem inflammatory 
syndrome in adults; MIS-C = multisystem inflammatory syndrome in children; PCR = polymerase chain reaction. 

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11.3. 
APPENDIX 3: CDC Working Case Definitions of Pericarditis, 
Myocarditis, and Myopericarditis Occurring After Receipt of 
COVID-19 mRNA Vaccines 
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 contained within the 
CDC case definition. Diagnostic evaluation (eg, electrocardiogram, echocardiogram) and 
laboratory testing (eg, troponin) included in the CDC definition (Table 11) must promptly be 
obtained in 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. The investigator 
will submit any updated myocarditis, pericarditis, or myopericarditis case data to the Sponsor 
within 24 hours of it being available. 
Table 11: 
Case Definitions of Probable and Confirmed Myocarditis, Pericarditis, and 
Myopericarditis 
Condition 
Definition 
Acute 
myocarditis 
Probable case 
Confirmed case 
Presence of ≥ 1 new or worsening of the 
following clinical symptoms: 
Presence of ≥ 1 new or worsening of 
the following clinical symptoms: 
• 
chest pain, pressure, or 
discomfort 
• 
chest pain, pressure, or 
discomfort 
• 
dyspnea, shortness of breath, or 
pain with breathing 
• 
dyspnea, shortness of breath, or 
pain with breathing 
• 
palpitations 
• 
palpitations 
• 
syncope 
• 
syncope 
OR, infants and children aged < 12 years 
might instead have ≥ 2 of the following 
symptoms: 
OR, infants and children aged 
< 12 years might instead have ≥ 2 of the 
following symptoms: 
• 
irritability 
• 
irritability 
• 
vomiting 
• 
vomiting 
• 
poor feeding 
• 
poor feeding 
• 
tachypnea 
• 
tachypnea 

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Condition 
Definition 
• 
lethargy 
• 
lethargy 
AND 
AND 
≥ 1 new finding of: 
≥ 1 new finding of: 
• 
troponin level above upper limit 
of normal (any type of troponin) 
• 
Histopathologic confirmation 
of myocarditisa 
• 
abnormal ECG or EKG or 
rhythm monitoring findings 
consistent with myocarditisb 
• 
abnormal cardiac function or 
wall motion abnormalities on 
echocardiogram 
• 
cMRI findings consistent with 
myocarditisc in the presence of 
troponin level above upper 
limit of normal (any type of 
troponin) 
• 
cMRI findings consistent with 
myocarditisc 
AND 
AND 
• 
No other identifiable cause of 
the symptoms and findings 
• 
No other identifiable cause of 
the symptoms and findings 
Acute 
pericarditisd 
Presence of ≥ 2 new or worsening of the following clinical features: 
• 
acute chest paine 
• 
pericardial rub on examination 
• 
new ST-elevation or PR-depression on EKG 
• 
new or worsening pericardial effusion on echocardiogram or MRI 
Myopericarditis This term may be used for patients who meet criteria for both myocarditis and 
pericarditis. 
Abbreviations: AV = atrioventricular; CEAC = cardiac event adjudication committee; cMRI = cardiac magnetic 
resonance imaging; ECG or EKG = electrocardiogram; MRI = magnetic resonance imaging. 
Note: An independent cardiac event adjudication committee (CEAC; see Section 8.12.3) comprised of medically 
qualified personnel, including cardiologists, will review suspected cases of myocarditis, pericarditis, and 
myopericarditis to determine if they meet Center for Disease Control and Prevention criteria for “probable” or 
“confirmed” events (Gargano et al 2021) and provide the assessment to the Sponsor. The CEAC members will be 
blinded to study treatment. Details regarding the CEAC composition, responsibilities, procedures, and frequency of 
data review will be defined in the CEAC charter. 
a. 
Using the Dallas criteria (Aretz et al 1987). 

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b. 
To meet the ECG or rhythm monitoring criterion, a probable case must include at least one of 1) ST-segment or 
T-wave abnormalities; 2) paroxysmal or sustained atrial, supraventricular, or ventricular arrhythmias; or 3) AV 
nodal conduction delays or intraventricular conduction defects. 
c. 
Using either the original or the revised Lake Louise criteria 
(https://www.sciencedirect.com/science/article/pii/S0735109718388430?via%3Dihubexternal icon). 
d. 
https://academic.oup.com/eurheartj/article/36/42/2921/2293375external icon. 
e. 
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 might occur. 
Reference: Gargano et al 2021. 
 

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