A Phase 3, Randomized, Stratified, Observer-Blind, Active-Controlled Study to Evaluate the Immunogenicity, Reactogenicity and Safety of mRNA-1010 Seasonal Influenza Vaccine in Adults 18 Years and Older
Phase: PHASE3
Conditions: Seasonal Influenza
Sponsor: ModernaTX, Inc.

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Page 1 
CLINICAL STUDY PROTOCOL 
Protocol Title: 
A Phase 3, randomized, stratified, observer-blind, active-
controlled study to evaluate the immunogenicity, reactogenicity, 
and safety of mRNA-1010 seasonal influenza vaccine in adults 
18 years and older 
Protocol Number: 
mRNA-1010-P303 
Amendment Number: 
2 
Date of Amendment 
11 Dec 2023 
Date of Amendment 1: 
10 Oct 2023 
Date of Original 
Protocol: 
28 Feb 2023 
Compound: 
mRNA-1010 
Brief Title: 
A Phase 3 study to evaluate the immunogenicity and safety of 
mRNA-1010 candidate seasonal influenza vaccine in adults  
Study Phase: 
3 
Sponsor Name: 
ModernaTX, Inc. 
Legal Registered 
Address: 
200 Technology Square 
Cambridge, MA 02139 
Regulatory Agency 
Identifier Number(s): 
Registry 
ID 
FDA 
IND 27460 
Sponsor Signatory:  
See e-Signature and date signed on last page of the document. 
Sponsor Signatory and Contact Information will be provided separately. 
CONFIDENTIAL 
This document contains confidential information, which should not be copied, referred to, 
released to, or published by anyone without written approval from ModernaTX, Inc. 

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DECLARATION OF INVESTIGATOR  
I have read and understood all sections of the protocol entitled A Phase 3, randomized, stratified, 
observer-blind, active-controlled study to evaluate the immunogenicity, reactogenicity and safety 
of mRNA-1010 seasonal influenza vaccine in adults 18 years and older, dated 11 Dec 2023 and 
the most recent version of the mRNA-1010 IB. 
I agree to supervise all aspects of the protocol and to conduct the clinical investigation in 
accordance with the current protocol, ICH, E6(R2) GCP Guidance, and all applicable local and 
country regulations. I will not make changes to the protocol before consulting with ModernaTX, 
Inc. or implement protocol changes without IRB approval except to eliminate an immediate risk 
to participants. 
I agree to administer study treatment only to participants under my personal supervision or the 
supervision of a 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 staff 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, regulations, and ICH E6(R2) GCP 
guidelines. 
 
Signature of Principal Investigator 
 
 
Date 
 
 
 
 
Printed Name of Principal Investigator 
 
 
 
 
 
 

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PROTOCOL AMENDMENT SUMMARY OF CHANGES  
 
DOCUMENT HISTORY 
Document 
Date 
Amendment 2 
11 Dec 2023 
Amendment 1 
10 Oct 2023 
Original Protocol 
28 Feb 2023 
Global Amendment 2, 11 Dec 2023: Current Amendment 
This amendment is considered to be substantial. 
Main Rationale for the Amendment: 
The main purpose of this amendment is to update the objectives and endpoints in Part B by 
moving immunogenicity objectives with corresponding endpoints from exploratory to primary 
(for noninferiority) and to secondary (for superiority). The summary of changes table describes 
these changes, including sections that are affected by these changes. 
Summary of Changes in Protocol Amendment 2: 
Section # and Name 
Description of Change 
Brief Rationale 
Title Page, Signature Page, 
Protocol Amendment Summary 
of Changes, Header 
Updated the protocol version and 
date, as applicable. 
To reflect the current 
version. 
Section 2.9.5.1 
(Immunogenicity Analysis, 
Part A) 
Immunogenicity analysis 
(paragraph 6) was changed from, 
“The primary analyses will be 
repeated using the Immunogenicity 
Set as a sensitivity analysis” to, 
“The primary analyses will be 
repeated using the Immunogenicity 
Set as a supplementary analysis”. 
To align with the FDA 
E9(R1) for Estimands. 
Section 3.1 (Protocol Synopsis, 
Part B) 
Section 3.1 (Protocol synopsis) was 
updated to align with changes in the 
relevant sections of Part B. 
To align with changes in 
relevant sections of Part B. 
Section 3.2 (Objectives and 
Endpoints, Part B) 
Added to primary objectives (Part B): 
• 
To evaluate the humoral 
immunogenicity (for 
noninferiority) of mRNA-1010 
relative to that of a licensed SD 
seasonal influenza vaccine 
(Fluarix Quadrivalent) against 
4 vaccine-matched influenza virus 
A and B strains at Day 29 in 
adults 18 to <65 years old 
To align with the change to 
establish immunogenicity 
of mRNA-1010 candidate 
seasonal influenza vaccine. 

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Section # and Name 
Description of Change 
Brief Rationale 
Moved from exploratory to secondary 
objectives (Part B): 
• 
To evaluate the immunological 
response of mRNA-1010 (for 
superiority) relative to a licensed 
SD seasonal influenza vaccine 
(Fluarix Quadrivalent) against 
vaccine-matched influenza A and 
B strains at Day 29. 
• 
To further evaluate the humoral 
immunogenicity of each study 
arm against vaccine-matched 
influenza A and B strains at Day 
29. 
Sections 3.3.1 and 4.3.1 
(Overall Design): Table 9 
(Part B), and Table 13 (Part C) 
Amount of mRNA/Antigen for 
treatment group 3 (Table 9) and 
treatment group 5 (Table 13) changed 
from 50 µg to 12.5 µg, and for 
treatment group 6 (Table 13) from 15 
µg to 60 µg. 
To correct an error in dose 
calculation of 
mRNA/antigen. 
Section 3.3.2 (Scientific 
Rationale for Study Design, 
Part B) 
Updated scientific rationale for study 
design in Part B. 
To align with updated 
objectives and endpoints. 
Section 3.9.2 (Statistical 
Hypothesis), and Section 3.9.3 
(Sample Size Determination, 
Part B) 
Statistical hypothesis and the sample 
size determination were updated in 
Part B. 
To align with the needed 
analyses for updated 
endpoints 
Section 3.9.7 (Multiplicity, 
Part B) 
Multiplicity adjustment criteria were 
updated. 
Figure 1 was moved from 
Section 4.9.7 to Section 3.9.7. 
To align with testing 
noninferiority and 
superiority hypotheses in 
Part B. 
Section 3.4.2 (Exclusion 
Criteria, Part B) and Section 
4.4.2 (Exclusion Criteria, 
Part C) 
Updated the exclusion criteria # 10 in 
Part B and Part C of the study.  
To provide clarity on heart 
muscle inflammation 
exclusion in Parts B and C. 
 

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TABLE OF CONTENTS 
CLINICAL STUDY PROTOCOL ..................................................................................................1 
DECLARATION OF INVESTIGATOR .........................................................................................2 
PROTOCOL AMENDMENT SUMMARY OF CHANGES ..........................................................3 
LIST OF ABBREVIATIONS AND DEFINITION OF TERMS ..................................................15 
1. 
INTRODUCTION ......................................................................................................17 
1.1. 
Study Rationale ...........................................................................................................17 
1.2. 
Background .................................................................................................................18 
1.3. 
Benefit/Risk Assessment ............................................................................................18 
1.3.1. 
Risk Assessment .........................................................................................................18 
1.3.2. 
Benefit Assessment .....................................................................................................19 
1.3.3. 
Overall Benefit/Risk Conclusion ................................................................................19 
2. 
PART A ......................................................................................................................20 
2.1. 
Protocol Summary ......................................................................................................20 
2.1.1. 
Synopsis (Part A) ........................................................................................................20 
2.1.2. 
SoA (Part A) ...............................................................................................................23 
2.2. 
Objectives and Endpoints (Part A) .............................................................................27 
2.3. 
Study Design (Part A) .................................................................................................28 
2.3.1. 
Overall Design (Part A) ..............................................................................................28 
2.3.2. 
Scientific Rationale for Study Design ........................................................................29 
2.3.3. 
Justification for Dose ..................................................................................................29 
2.3.4. 
End of Study Definition ..............................................................................................29 
2.4. 
Study Population (Part A) ...........................................................................................29 
2.4.1. 
Inclusion Criteria (Part A) ..........................................................................................30 
2.4.2. 
Exclusion Criteria (Part A) .........................................................................................30 
2.4.3. 
Screen Failures ............................................................................................................33 
2.4.4. 
Criteria for Temporarily Delaying the Day 1 Visit ....................................................33 
2.5. 
Study Intervention(s) and Concomitant Therapy (Part A) .........................................33 
2.5.1. 
Study Intervention(s) Administered ...........................................................................34 
2.5.2. 
Preparation, Handling, Storage, and Accountability ..................................................35 
2.5.2.1. 
Study Intervention(s) Preparation ...............................................................................35 
2.5.2.2. 
Study Intervention(s) Administration .........................................................................35 

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2.5.2.3. 
Study Intervention(s) Packaging and Labeling ...........................................................36 
2.5.2.4. 
Study Intervention(s) Storage .....................................................................................36 
2.5.2.5. 
Study Intervention(s) Accountability .........................................................................36 
2.5.2.6. 
Study Intervention(s) Handling and Disposal .............................................................37 
2.5.2.7. 
Unblinding ..................................................................................................................37 
2.6. 
Assignment to Study Intervention (Part A) ................................................................37 
2.6.1. 
Blinding ......................................................................................................................37 
2.6.2. 
Study Intervention Compliance ..................................................................................38 
2.6.3. 
Dose Modification ......................................................................................................38 
2.6.4. 
Continued Access to Study Intervention After the End of the Study .........................38 
2.6.5. 
Treatment of Overdose ...............................................................................................38 
2.6.6. 
Prior and Concomitant Therapy ..................................................................................38 
2.6.6.1. 
Prohibited Therapy .....................................................................................................38 
2.6.6.2. 
Recording of Concomitant Medications, Concomitant Vaccinations and 
Concomitant Procedures .............................................................................................39 
2.6.6.3. 
Concomitant Medications and Vaccines That May Lead to the Elimination of 
a Participant From Per-protocol Analyses ...................................................................39 
2.7. 
Discontinuation of Study Intervention and Participant 
Discontinuation/Withdrawal (Part A) .........................................................................40 
2.7.1. 
Discontinuation of Study Intervention........................................................................40 
2.7.1.1. 
Participant Discontinuation/Withdrawal from the Study ...........................................40 
2.7.1.2. 
Lost to Follow-up .......................................................................................................41 
2.7.2. 
Pause Rules .................................................................................................................42 
2.8. 
Study Assessments and Procedures (Part A) ..............................................................42 
2.8.1. 
Demography ...............................................................................................................42 
2.8.2. 
Immunogenicity Assessments ....................................................................................43 
2.8.3. 
Safety Assessments .....................................................................................................43 
2.8.3.1. 
Physical Examinations ................................................................................................43 
2.8.3.2. 
Vital Signs ..................................................................................................................44 
2.8.3.3. 
Pregnancy Testing ......................................................................................................44 
2.8.3.4. 
Assessments for Respiratory Viral Infections (Part A Only) .....................................44 
2.8.3.5. 
Safety Phone Calls ......................................................................................................45 
2.8.3.6. 
Use of Electronic Diaries ............................................................................................45 

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2.8.3.7. 
Ancillary Supplies for Participant Use .......................................................................46 
2.8.3.8. 
AEs, SAEs, and Other Safety Reporting ....................................................................46 
2.8.3.9. 
Solicited Adverse Reactions .......................................................................................48 
2.8.3.10. 
Medically Attended Adverse Events ..........................................................................49 
2.8.3.11. 
Adverse Events of Special Interest .............................................................................49 
2.8.4. 
Pharmacokinetics ........................................................................................................51 
2.8.5. 
Pharmacodynamics .....................................................................................................51 
2.8.6. 
Genetics ......................................................................................................................51 
2.8.7. 
Biomarkers ..................................................................................................................51 
2.8.8. 
Immunogenicity Assessments ....................................................................................51 
2.8.9. 
Health Economics or Medical Resource Utilization and Health Economics .............52 
2.9. 
Statistical Considerations (Part A) ..............................................................................52 
2.9.1. 
Blinding and Responsibility for Analyses ..................................................................52 
2.9.2. 
Statistical Hypotheses .................................................................................................53 
2.9.3. 
Sample Size Determination ........................................................................................53 
2.9.4. 
Analysis Sets ...............................................................................................................54 
2.9.5. 
Statistical Analyses .....................................................................................................55 
2.9.5.1. 
Immunogenicity Analyses ..........................................................................................55 
2.9.5.2. 
Adverse Events ...........................................................................................................56 
2.9.5.3. 
Exploratory Analyses ..................................................................................................56 
2.9.6. 
Planned Analyses ........................................................................................................57 
2.9.6.1. 
Primary Analyses ........................................................................................................57 
2.9.6.2. 
Final Analysis .............................................................................................................57 
2.9.7. 
Multiplicity .................................................................................................................57 
3. 
PART B ......................................................................................................................58 
3.1. 
Protocol Summary ......................................................................................................58 
3.1.1. 
Synopsis (Part B) ........................................................................................................58 
3.1.2. 
SoA (Part B) ...............................................................................................................61 
3.2. 
Objectives and Endpoints (Part B) .............................................................................64 
3.3. 
Study Design (Part B) .................................................................................................65 
3.3.1. 
Overall Design (Part B) ..............................................................................................65 
3.3.2. 
Scientific Rationale for Study Design ........................................................................66 
3.3.3. 
Justification for Dose ..................................................................................................66 

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3.3.4. 
End of Study Definition ..............................................................................................66 
3.4. 
Study Population (Part B) ...........................................................................................66 
3.4.1. 
Inclusion Criteria (Part B) ..........................................................................................66 
3.4.2. 
Exclusion Criteria (Part B) .........................................................................................67 
3.4.3. 
Screen Failures ............................................................................................................70 
3.4.4. 
Criteria for Temporarily Delaying the Day 1 Visit ....................................................70 
3.5. 
Study Intervention(s) and Concomitant Therapy (Part B) ..........................................70 
3.5.1. 
Study Intervention(s) Administered ...........................................................................70 
3.5.2. 
Preparation, Handling, Storage, and Accountability ..................................................71 
3.5.2.1. 
Study Intervention(s) Preparation ...............................................................................71 
3.5.2.2. 
Study Intervention(s) Administration .........................................................................71 
3.5.2.3. 
Study Intervention(s) Packaging and Labeling ...........................................................72 
3.5.2.4. 
Study Intervention(s) Storage .....................................................................................72 
3.5.2.5. 
Study Intervention(s) Accountability .........................................................................72 
3.5.2.6. 
Study Intervention(s) Handling and Disposal .............................................................72 
3.5.2.7. 
Unblinding ..................................................................................................................72 
3.6. 
Assignment to Study Intervention (Part B) ................................................................72 
3.6.1. 
Blinding ......................................................................................................................72 
3.6.2. 
Study Intervention Compliance ..................................................................................72 
3.6.3. 
Dose Modification ......................................................................................................73 
3.6.4. 
Continued Access to Study Intervention After the End of the Study .........................73 
3.6.5. 
Treatment of Overdose ...............................................................................................73 
3.6.6. 
Prior and Concomitant Therapy ..................................................................................73 
3.6.6.1. 
Prohibited Therapy .....................................................................................................73 
3.6.6.2. 
Recording of Concomitant Medications, Concomitant Vaccinations and 
Concomitant Procedures .............................................................................................73 
3.6.6.3. 
Concomitant Medications and Vaccines That May Lead to the Elimination of 
a Participant From Per-protocol Analyses ...................................................................73 
3.7. 
Discontinuation of Study Intervention and Participant 
Discontinuation/Withdrawal (Part B) .........................................................................73 
3.7.1. 
Discontinuation of Study Intervention........................................................................73 
3.7.2. 
Participant Discontinuation/Withdrawal from the Study ...........................................73 
3.7.3. 
Lost to Follow-up .......................................................................................................73 

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3.7.4. 
Pause Rules .................................................................................................................73 
3.8. 
Study Assessments and Procedures (Part B) ..............................................................73 
3.8.1. 
Demography ...............................................................................................................74 
3.8.2. 
Immunogenicity Assessments ....................................................................................74 
3.8.3. 
Safety Assessments .....................................................................................................74 
3.8.3.1. 
Physical Examinations ................................................................................................74 
3.8.3.2. 
Vital Signs ..................................................................................................................74 
3.8.3.3. 
Pregnancy Testing ......................................................................................................74 
3.8.3.4. 
Safety Phone Calls ......................................................................................................74 
3.8.3.5. 
Use of Electronic Diaries ............................................................................................74 
3.8.3.6. 
Ancillary Supplies for Participant Use .......................................................................74 
3.8.3.7. 
AEs, SAEs, and Other Safety Reporting ....................................................................74 
3.8.3.8. 
Solicited Adverse Reactions .......................................................................................75 
3.8.3.9. 
Medically Attended Adverse Events ..........................................................................75 
3.8.3.10. 
Adverse Events of Special Interest .............................................................................75 
3.8.4. 
Pharmacokinetics ........................................................................................................75 
3.8.5. 
Pharmacodynamics .....................................................................................................75 
3.8.6. 
Genetics ......................................................................................................................75 
3.8.7. 
Biomarkers ..................................................................................................................75 
3.8.8. 
Immunogenicity Assessments ....................................................................................76 
3.8.9. 
Health Economics or Medical Resource Utilization and Health Economics .............76 
3.9. 
Statistical Considerations (Part B) ..............................................................................76 
3.9.1. 
Blinding and Responsibility for Analyses ..................................................................76 
3.9.2. 
Statistical Hypotheses .................................................................................................76 
3.9.3. 
Sample Size Determination ........................................................................................77 
3.9.4. 
Analysis Sets ...............................................................................................................78 
3.9.5. 
Statistical Analyses .....................................................................................................78 
3.9.5.1. 
Immunogenicity Analyses ..........................................................................................78 
3.9.5.2. 
Adverse Events ...........................................................................................................78 
3.9.5.3. 
Exploratory Analyses ..................................................................................................78 
3.9.6. 
Planned Analyses ........................................................................................................78 
3.9.6.1. 
Primary Analyses ........................................................................................................78 
3.9.6.2. 
Final Analysis .............................................................................................................78 

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3.9.7. 
Multiplicity .................................................................................................................78 
4. 
PART C ......................................................................................................................80 
4.1. 
Protocol Summary ......................................................................................................80 
4.1.1. 
Synopsis (Part C) ........................................................................................................80 
4.1.2. 
SoA (Part C) ...............................................................................................................83 
4.2. 
Objectives and Endpoints (Part C) .............................................................................86 
4.3. 
Study Design (Part C) .................................................................................................87 
4.3.1. 
Overall Design (Part C) ..............................................................................................87 
4.3.2. 
Scientific Rationale for Study Design ........................................................................88 
4.3.3. 
Justification for Dose ..................................................................................................88 
4.3.4. 
End of Study Definition ..............................................................................................88 
4.4. 
Study Population (Part C) ...........................................................................................89 
4.4.1. 
Inclusion Criteria (Part C) ..........................................................................................89 
4.4.2. 
Exclusion Criteria (Part C) .........................................................................................89 
4.4.3. 
Screen Failures ............................................................................................................91 
4.4.4. 
Criteria for Temporarily Delaying the Day 1 Visit ....................................................91 
4.5. 
Study Intervention(s) and Concomitant Therapy (Part C) ..........................................91 
4.5.1. 
Study Intervention(s) Administered ...........................................................................92 
4.5.2. 
Preparation, Handling, Storage, and Accountability ..................................................93 
4.5.2.1. 
Study Intervention(s) Preparation ...............................................................................93 
4.5.2.2. 
Study Intervention(s) Administration .........................................................................93 
4.5.2.3. 
Study Intervention(s) Packaging and Labeling ...........................................................93 
4.5.2.4. 
Study Intervention(s) Storage .....................................................................................93 
4.5.2.5. 
Study Intervention(s) Accountability .........................................................................94 
4.5.2.6. 
Study Intervention(s) Handling and Disposal .............................................................94 
4.5.2.7. 
Unblinding ..................................................................................................................94 
4.6. 
Assignment to Study Intervention (Part C) ................................................................94 
4.6.1. 
Blinding ......................................................................................................................94 
4.6.2. 
Study Intervention Compliance ..................................................................................94 
4.6.3. 
Dose Modification ......................................................................................................94 
4.6.4. 
Continued Access to Study Intervention After the End of the Study .........................94 
4.6.5. 
Treatment of Overdose ...............................................................................................94 
4.6.6. 
Prior and Concomitant Therapy ..................................................................................94 

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4.6.6.1. 
Prohibited Therapy .....................................................................................................94 
4.6.6.2. 
Recording of Concomitant Medications, Concomitant Vaccinations and 
Concomitant Procedures .............................................................................................95 
4.6.6.3. 
Concomitant Medications and Vaccines That May Lead to the Elimination of 
a Participant From Per-protocol Analyses ...................................................................95 
4.7. 
Discontinuation of Study Intervention and Participant 
Discontinuation/Withdrawal (Part C) .........................................................................95 
4.7.1. 
Discontinuation of Study Intervention........................................................................95 
4.7.2. 
Participant Discontinuation/Withdrawal from the Study ...........................................95 
4.7.3. 
Lost to Follow-up .......................................................................................................95 
4.7.4. 
Pause Rules .................................................................................................................95 
4.8. 
Study Assessments and Procedures (Part C) ..............................................................95 
4.8.1. 
Demography ...............................................................................................................95 
4.8.2. 
Immunogenicity Assessments ....................................................................................95 
4.8.3. 
Safety Assessments .....................................................................................................96 
4.8.3.1. 
Physical Examinations ................................................................................................96 
4.8.3.2. 
Vital Signs ..................................................................................................................96 
4.8.3.3. 
Safety Phone Calls ......................................................................................................96 
4.8.3.4. 
Use of Electronic Diaries ............................................................................................96 
4.8.3.5. 
Ancillary Supplies for Participant Use .......................................................................96 
4.8.3.6. 
AEs, SAEs, and Other Safety Reporting ....................................................................96 
4.8.3.7. 
Solicited Adverse Reactions .......................................................................................97 
4.8.3.8. 
Medically Attended Adverse Events ..........................................................................97 
4.8.3.9. 
Adverse Events of Special Interest .............................................................................97 
4.8.4. 
Pharmacokinetics ........................................................................................................97 
4.8.5. 
Pharmacodynamics .....................................................................................................97 
4.8.6. 
Genetics ......................................................................................................................97 
4.8.7. 
Biomarkers ..................................................................................................................97 
4.8.8. 
Immunogenicity Assessments ....................................................................................97 
4.8.9. 
Health Economics or Medical Resource Utilization and Health Economics .............97 
4.9. 
Statistical Considerations (Part C) ..............................................................................97 
4.9.1. 
Blinding and Responsibility for Analyses ..................................................................97 
4.9.2. 
Statistical Hypotheses .................................................................................................98 

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4.9.3. 
Sample Size Determination ........................................................................................99 
4.9.4. 
Analysis Sets ...............................................................................................................99 
4.9.5. 
Statistical Analyses .....................................................................................................99 
4.9.5.1. 
Immunogenicity Analyses ..........................................................................................99 
4.9.5.2. 
Adverse Events .........................................................................................................100 
4.9.5.3. 
Exploratory Analyses ................................................................................................100 
4.9.6. 
Planned Analyses ......................................................................................................100 
4.9.6.1. 
Primary Analyses ......................................................................................................100 
4.9.6.2. 
Final Analysis ...........................................................................................................100 
4.9.7. 
Multiplicity ...............................................................................................................100 
5. 
SUPPORTING DOCUMENTATION AND OPERATIONAL 
CONSIDERATIONS ................................................................................................101 
5.1. 
Appendix 1: Regulatory, Ethical, and Study Oversight Considerations ..................101 
5.1.1. 
Regulatory and Ethical Considerations ....................................................................101 
5.1.2. 
Financial Disclosure .................................................................................................101 
5.1.3. 
Informed Consent Process ........................................................................................102 
5.1.4. 
Recruitment Strategy ................................................................................................102 
5.1.5. 
Data Protection .........................................................................................................102 
5.1.6. 
Committee Structure .................................................................................................103 
5.1.6.1. 
Internal Safety Team .................................................................................................103 
5.1.6.2. 
Cardiac Event Adjudication Committee ...................................................................103 
5.1.7. 
Dissemination of Clinical Study Data ......................................................................103 
5.1.8. 
Data Quality Assurance ............................................................................................103 
5.1.9. 
Source Documents ....................................................................................................104 
5.1.10. 
Study and Site Start Closure .....................................................................................105 
5.1.11. 
Publication Policy .....................................................................................................105 
5.2. 
Appendix 2: Clinical Laboratory Tests .....................................................................106 
5.3. 
Appendix 3: AEs and SAEs: Definitions and Procedures for Recording, 
Evaluating, Follow-up, and Reporting ......................................................................107 
5.3.1. 
Definition of AE .......................................................................................................107 
5.3.2. 
Definition of SAE .....................................................................................................108 
5.3.3. 
Definition of MAAE .................................................................................................108 
5.3.4. 
Definition of AESI ....................................................................................................109 

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5.3.5. 
Recording and Follow-up of AE and/or SAE ...........................................................109 
5.3.6. 
Reporting of SAEs/AESI ..........................................................................................112 
5.4. 
Appendix 4: Adverse Event of Special Interest ........................................................113 
5.5. 
Appendix 5: CDC Working Case Definitions of Pericarditis, Myocarditis, 
and Myopericarditis Occurring After Receipt of COVID-19 mRNA 
Vaccines ....................................................................................................................114 
5.6. 
Appendix 6: Contraceptive and Barrier Guidance ....................................................116 
5.6.1. 
Definitions ................................................................................................................116 
5.6.2. 
Contraception Guidance ...........................................................................................117 
5.7. 
Appendix 7: Protocol Amendment History ..............................................................119 
5.7.1. 
Global Amendment 1, 10 Oct 2023: .........................................................................119 
6. 
REFERENCES .........................................................................................................122 

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LIST OF TABLES  
Table 1: 
Schedule of Activities (Part A) ...................................................................................23 
Table 2: 
Objectives and Endpoints (Part A) .............................................................................27 
Table 3: 
Treatment Groups and Dose Levels (Part A) .............................................................28 
Table 4: 
Study Intervention(s) Administered ...........................................................................34 
Table 5: 
Respiratory and Systemic Symptoms for Protocol-defined Influenza-like 
Illness ..........................................................................................................................51 
Table 6: 
Populations for Analysis .............................................................................................54 
Table 7: 
Schedule of Activities (Part B) ...................................................................................61 
Table 8: 
Objectives and Endpoints (Part B) .............................................................................64 
Table 9: 
Treatment Groups and Dose Levels (Part B) ..............................................................65 
Table 10: Study Intervention(s) Administered ...........................................................................70 
Table 11: Schedule of Activities (Part C) ...................................................................................83 
Table 12: Objectives and Endpoints (Part C) .............................................................................86 
Table 13: Treatment Groups and Dose Levels (Part C) ..............................................................87 
Table 14: Study Intervention(s) Administered ...........................................................................92 
Table 15: Protocol-required Safety Laboratory Tests ...............................................................106 
Table 16: Adult and Adolescent Solicited Adverse Reactions and Grades ..............................110 
Table 17: Adverse Events of Special Interest ...........................................................................113 
Table 18: Case Definitions of Probably and Confirmed Myocarditis, Pericarditis, and 
Myopericarditis .........................................................................................................114 
LIST OF FIGURES  
Figure 1: 
Prespecified Order for Superiority Hypothesis Testing ..............................................79 

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LIST OF ABBREVIATIONS AND DEFINITION OF TERMS  
The following abbreviations and terms are used in this study protocol. 
Abbreviation or Specialist Term 
Definition 
AE 
Adverse event 
AESI 
Adverse event of special interest 
AFAB 
Assigned female at birth 
ANCOVA 
Analysis of covariance 
AR 
Adverse reaction 
CDC 
Centers for Disease Control and Prevention 
CEAC 
Cardiac Event Adjudication Committee 
CFR 
Code of Federal Regulations 
CI 
Confidence interval 
COVID-19 
Coronavirus disease 2019 
CRO 
Contract research organization 
CSR 
Clinical study report 
DHHS 
Department of Health and Human Services 
eCRF 
Electronic case report form 
EDC 
Electronic data capture 
eDiary 
Electronic diary 
EoS 
End of study 
FAS 
Full Analysis Set 
FDA 
Food and Drug Administration 
FSH 
Follicle-stimulating hormone 
GCP 
Good Clinical Practice 
GLSM 
Geometric least square mean 
GMFR 
Geometric mean fold rise 
GMR 
Geometric mean ratio 
GMT 
Geometric mean titer 
HA 
Hemagglutinin 
HAI 
Hemagglutination inhibition 
HCP 
Healthcare practitioner 
HD 
High dose 
HIV 
Human immunodeficiency virus 

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Abbreviation or Specialist Term 
Definition 
HRT 
Hormonal replacement therapy 
IB 
Investigator’s brochure 
ICF 
Informed consent form 
ICH 
International Council for Harmonisation of Technical 
Requirements for Pharmaceuticals for Human Use 
ILI 
Influenza-like illness 
IM 
Intramuscular(ly) 
IND 
Investigational new drug 
IRB 
Institutional Review Board 
IRT 
Interactive response technology 
IST 
Internal safety team 
LNP 
Lipid nanoparticle 
LTFU 
Lost to follow-up 
MAAE 
Medically attended adverse event 
MedDRA 
Medical Dictionary for Regulatory Activities 
(m)RNA 
(Messenger) ribonucleic acid 
NH 
Northern Hemisphere 
NP 
Nasopharyngeal 
POCBP 
Person of childbearing potential 
PONCBP 
Person of nonchildbearing potential 
PP 
Per-protocol 
QTLs 
Quality tolerance limits 
RNA 
Ribonucleic acid 
RT-PCR 
Reverse transcription polymerase chain reaction 
SAE 
Serious adverse event 
SAP 
Statistical analysis plan 
SCR 
Seroconversion rate 
SD 
Standard dose 
SH 
Southern Hemisphere 
SoA 
Schedule of Activities 
WHO 
World Health Organization 

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1. 
INTRODUCTION  
Seasonal influenza viruses are estimated by the WHO to cause 3 to 5 million cases of severe 
illness and up to 650,000 deaths each year, which is a severe challenge to public health 
(WHO 2023). Influenza epidemics occur each year and follow a seasonal circulation pattern with 
increased cases during the winter months in the NH and SH, respectively (Riedel et al 2019). 
Since influenza viruses continuously change through a process termed antigenic drift, the 
circulating viruses are actively monitored by a worldwide monitoring network coordinated by the 
WHO (Monto 2018). Based on the observed circulation patterns and antigenic changes, an expert 
panel recommends influenza virus strains to be used for vaccine manufacturing twice a year 
(once for the NH and once for the SH). Influenza A and B viruses are the most relevant influenza 
viruses for human infection. Therefore, current vaccine recommendations include 1 influenza A 
H1N1 strain, 1 influenza A H3N2 strain, and 2 influenza B strains (covering the B/Victoria and 
B/Yamagata lineages) (WHO 2023a, WHO 2023b). 
Currently licensed seasonal influenza virus vaccines rarely exceed 60% overall effectiveness and 
are poorly effective during the years when circulating viruses do not match the strains selected 
for the vaccine antigens (CDC 2023a). Influenza vaccines based on mRNA technology could 
provide several benefits compared with current vaccines, including the ability to respond to 
strain changes more quickly, avoidance of mutations that may be acquired during vaccine 
production in eggs or cell culture, stronger immune responses, and improved protection in older 
adults (Rockman et al 2020). 
The Sponsor has developed a rapid response proprietary vaccine platform based on an mRNA 
delivery system. The platform is based on the principle and observations that cells in vivo can 
take up mRNA, translate it, and then express protein viral antigens(s) on the cell surface. The 
delivered mRNA does not enter the cellular nucleus or interact with the genome, is 
nonreplicating, and is expressed transiently. 
ModernaTX, Inc. (the Sponsor) is using its mRNA-based platform to develop an 
LNP-encapsulated mRNA-based vaccine against disease caused by influenza virus types A and 
B. The proposed development candidate, mRNA-1010, is a quadrivalent vaccine containing 
mRNAs that encode for the HA of the 4 strains recommended by the WHO for cell or 
recombinant-based vaccines. Equal amounts of mRNAs encoding for each of the 4 different 
strains will be used for the HA components. The mRNA-1010 development candidate is 
administered as a single IM injection and aims to elicit protection from all seasonal influenza 
viruses covered by the vaccine. 
1.1. 
Study Rationale  
The Sponsor is conducting this Phase 3 study (mRNA-1010-P303) of its seasonal influenza 
mRNA vaccine (mRNA-1010) in 3 parts (Part A, Part B, and Part C), to establish 
immunogenicity and safety in support of licensure. The design of this study will include 
immunogenicity objectives for HAI, a surrogate endpoint of prevention of influenza illness and 
its complications. The rationale for this approach is based on the established precedent of using 
HA-based immunologic correlates for clinical assessment and licensure of influenza vaccines 
(DHHS 2007a, DHHS 2007b, Dunning et al 2016, European Medicines Agency 2016). The 
Sponsor has optimized mRNA-1010, previously studied, to 
 
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1.2. 
Background  
mRNA-1010 is an LNP-encapsulated, mRNA-based, prophylactic vaccine containing 4 mRNAs 
in an equivalent mRNA mass ratio that encode membrane-bound HA of the 4 different influenza 
strains, recommended by the WHO for 2022 to 2023 (Part A) and 2023 to 2024 (Parts B, and C) 
NH cell or recombinant-based vaccines. 
The Sponsor has completed a Phase 1/2 study of mRNA-1010 (mRNA-1010-P101, 
NCT04956575) at dose levels up to 200 µg and is now conducting two Phase 3 studies at a 
50-µg dose level: mRNA-1010-P301, a safety and immunogenicity study (NCT05415462) and 
mRNA-1010-P302, a safety and efficacy study (NCT05566639). 
Data from study mRNA-1010-P101 Phase 2 NH suggest an improved and more durable immune 
response against influenza A strains compared to a licensed seasonal influenza vaccine at Day 29, 
Day 91, and Day 181. No safety concerns were identified. The 50-µg dose was chosen for the Phase 3 
studies based on the observed reactogenicity and immunogenicity profile. Interim results at Day 29 
from the Phase 3 mRNA-1010-P301 study indicate no safety concerns. Compared to licensed influenza 
vaccine, mRNA-1010 achieved superiority on seroconversion rates for A/H3N2 and A/H1N1, as well 
as superiority on geometric mean titer ratios for A/H3N2 and non-inferiority on geometric mean titer 
ratios for A/H1N1. Noninferiority was not met for either endpoint for the influenza B/Victoria- and 
B/Yamagata-lineage strains. In order to improve the immune response to the influenza B strains, the 
Sponsor has since optimized mRNA-1010 (see Section 1.1). 
Additional details of mRNA-1010 are provided in the IB. 
1.3. 
Benefit/Risk Assessment  
1.3.1. 
Risk Assessment  
There have been very rare (<1 in 10,000 recipients) reports of myocarditis and pericarditis 
occurring after vaccination with COVID-19 vaccines, including mRNA vaccines. The majority 
of the cases have been reported in adolescent and young adult persons assigned male at birth 
shortly after the second dose of the vaccine. These are typically mild cases and individuals tend 
to recover within a short time following standard treatment and rest (Gargano et al 2021). 
Investigators and participants should be alert to the signs and symptoms of myocarditis and 
pericarditis (see Section 5.5). The risk of myocarditis or pericarditis after administration of 
non-coronavirus disease mRNA vaccines is unknown. 
Safety and reactogenicity data from a Phase 1/2 study of mRNA-1010 (mRNA-1010-P101, 
NCT04956575) with dose levels up to 200 µg revealed no safety concerns. Additional details are 
provided in the IB. 
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1.3.2. 
Benefit Assessment  
Participants will obtain information about their general health status through the medical 
evaluations/assessments associated with this study (ie, physical examination, vital signs 
measurement). 
Participants will be contributing to the process of developing a new potentially prophylactic 
measure for influenza infection. 
1.3.3. 
Overall Benefit/Risk Conclusion  
Considering the safety data for mRNA-1010 to date, the Sponsor considers the potential benefits 
of participation to exceed the risks. 

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2. 
PART A  
2.1. 
Protocol Summary  
2.1.1. 
Synopsis (Part A)  
Protocol Title: A Phase 3, randomized, stratified, observer-blind, active-controlled study to 
evaluate the immunogenicity, reactogenicity, and safety of mRNA-1010 seasonal influenza 
vaccine in adults 18 years and older 
Brief Title: A Phase 3 study to evaluate the immunogenicity and safety of mRNA-1010 
candidate seasonal influenza vaccine in adults. 
Regulatory Agency Identifier Number(s): 
Registry 
FDA 
ID 
IND 27460 
Rationale:  
The Sponsor is conducting Part A of this Phase 3 study of its candidate seasonal influenza 
mRNA vaccine (mRNA-1010), mRNA-1010-P303, to establish immunogenicity and safety in 
support of licensure. The design of this study will include immunogenicity objectives for HAI, a 
surrogate endpoint of prevention of influenza illness and its complications. The rationale for this 
approach is based on the established precedent of using HA-based immunologic correlates for 
clinical assessment and licensure of influenza vaccines (DHHS 2007a, DHHS 2007b, Dunning et 
al 2016, European Medicines Agency 2016). The Sponsor has optimized mRNA-1010, 
previously studied in 2 previous Phase 3 trials, 
 
 
 
 
Objectives and Endpoints: 
Objectives 
Endpoints 
Primary 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed active 
comparator (Fluarix® Quadrivalent) against 
4 vaccine-matched influenza virus A and B 
strains at Day 29. 
• 
GMT at Day 29 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 29 as measured by 
HAI. 
• 
To evaluate the reactogenicity and safety of 
mRNA-1010. 
• 
Solicited local and systemic ARs through 
7 days after study intervention dosing. 
• 
Unsolicited AEs through 28 days after 
study intervention dosing. 
• 
MAAEs from Day 1 to Day 181/EoS. 
• 
AESI from Day 1 to Day 181/EoS. 
• 
SAEs from Day 1 to Day 181/EoS. 
• 
AEs leading to discontinuation from study 
participation from Day 1 to Day 181/EoS. 
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Objectives 
Endpoints 
Secondary 
• 
To further evaluate the humoral immunogenicity 
of mRNA-1010 against 4 vaccine-matched 
influenza virus A and B strains at Day 29. 
• 
The proportion of participants with HAI 
titer ≥1:40 at Day 29. 
• 
GMFR comparing Day 29 to Day 1 
(Baseline) as measured by HAI. 
Exploratory (May be Performed) 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed active 
comparator (Fluarix Quadrivalent) against 4 
vaccine-matched influenza virus A and B strains 
at Day 181/EoS. 
• 
GMT at Day 181 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 181 as measured by 
HAI. 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed active 
comparator against vaccine-matched or vaccine-
mismatched A and B strains, including the use of 
alternative methods. 
• 
GMT and GMFR of nAbs by assays such 
as MN assays or alternative methods 
against vaccine-matched or vaccine-
mismatched strains on Day 29 compared 
with Day 1 (Baseline). 
• 
GMT and GMFR of anti-HA antibodies as 
measured by HAI against vaccine-
mismatched strains on Day 29 compared 
with Day 1 (Baseline). 
• 
To assess the occurrence of clinical influenza in 
study participants and characterize their immune 
response to infection and viral isolates. 
• 
Frequency of RT-PCR-confirmed ILI and 
assessment of immune responses in 
participants with RT-PCR-confirmed ILI. 
Abbreviations: AE = adverse event; AESI = adverse events of special interest; AR = adverse reactions; EoS = end of 
study; GMFR = geometric mean fold rise; GMT = geometric mean titer; HA = hemagglutinin; 
HAI = hemagglutination inhibition; ILI = influenza-like illness; MN = microneutralization; MAAE = medically 
attended adverse event; mRNA = messenger ribonucleic acid; nAb=neutralizing antibody; RT-PCR = reverse 
transcription polymerase chain reaction; SAE = serious adverse event. 
Overall Design Synopsis: 
mRNA-1010-P303 Part A is a Phase 3, randomized, stratified, observer-blind, active-controlled 
study to evaluate the immunogenicity, reactogenicity, and safety of mRNA-1010 seasonal 
influenza vaccine in adults 18 years and older. 
Approximately 2400 medically stable adults at least 18 years of age inclusive, at the time of 
signing the ICF will be randomly assigned to treatment in this study in a 1:1: ratio to 1 of 2 
treatment groups to receive either a single dose of mRNA-1010 or a single dose of a licensed 
seasonal influenza vaccine as an active comparator (Fluarix Quadrivalent) at Day 1. 
Randomization will be stratified by age categories (18 to <50 years old, ≥50 to <65 years old, or 
≥65 years old) and influenza vaccine status in the prior 12 months (received or not received). 
Brief Summary: 
The study aims to demonstrate noninferiority of mRNA-1010 versus a licensed quadrivalent 
seasonal influenza vaccine (an active comparator) in the immune response, as measured by GMT 
and by seroconversion rate at Day 29, using HAI assay, for each of the 4 vaccine-matched 
influenza virus A and B strains. 

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Study details include: 
• There will be 4 clinic/in-person visits (Screening Visit and at Days 1, 29 and Day 181 
(Month 6)/EoS) and 2 safety phone calls at Days 8 and 91 as specified in the SoA. 
The Screening Visit and Day 1 may be performed on the same day or a different day. 
• All participants will be asked to complete an eDiary for solicited ARs for 7 days (ie, 
the day of study intervention dosing and 6 subsequent days). 
• Detection of all AEs will be through 28 days after study intervention dosing (ie, the 
day of study intervention dosing and 27 subsequent days). Detecting MAAEs, AESI, 
SAEs, and AEs leading to discontinuation from study participation will continue 
through Day 181 (Month 6)/EoS. 
Number of Participants: Approximately 2400 participants will be enrolled in Part A. 
Study Arms and Duration: 
• The study will comprise 2 study arms: investigational vaccine (mRNA-1010) group 
and active comparator (a licensed quadrivalent seasonal influenza vaccine) group. 
• The total study duration (including Screening) for each participant is up to 7 months. 

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2.1.2. 
SoA (Part A)  
Table 1: 
Schedule of Activities (Part A)  
Visit Number 
 
1 
2 
3 
4 
5 
USV 
Notes 
Type of Visit 
C 
C 
SC 
C 
SC 
C 
C 
 
Month Timepoint 
 
 
 
M1 
M3 
M6 
Up to M6 
 
Visit Day  
Screeninga 
D1 
(Baseline) 
D8 
D29 
D91 
D181/ 
EoS 
N/A 
 
Window Allowance (Days) 
-28 
N/A 
+3 
-7 to +3 
±5 
±14 
N/A 
 
Informed consent form, 
demographics, concomitant 
medications, medical historyb 
X 
 
 
 
 
 
 
 
Inclusion/exclusion criteria 
X 
X 
 
 
 
 
 
Refer to Section 2.4.1 and 
Section 2.4.2 
Physical examinationb 
X 
 
 
 
 
 
 
Refer to Section 2.8.3.1 
Vital signs measurements 
X 
X 
 
 
 
 
 
Refer to Section 2.8.3.2 
Pregnancy testing 
X 
X 
 
 
 
 
 
Prior to study intervention dosing 
on Day 1 
Refer to Section 2.8.3.3 
Randomization 
 
X 
 
 
 
 
 
Refer to Section 2.6 
Blood collection for future 
research sample (optional)  
 
X 
 
 
 
 
 
Prior to study intervention dosing 
Refer to Section 2.8.6 and 
Section 5.1.3 
Blood collection for 
transcriptomics (optional)  
 
X 
 
X 
 
 
 
Prior to study intervention dosing 
on Day 1 
Refer to Section 2.8.7  

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Visit Number 
 
1 
2 
3 
4 
5 
USV 
Notes 
Type of Visit 
C 
C 
SC 
C 
SC 
C 
C 
 
Month Timepoint 
 
 
 
M1 
M3 
M6 
Up to M6 
 
Visit Day  
Screeninga 
D1 
(Baseline) 
D8 
D29 
D91 
D181/ 
EoS 
N/A 
 
Window Allowance (Days) 
-28 
N/A 
+3 
-7 to +3 
±5 
±14 
N/A 
 
Study intervention dosing 
(including 30-minute, 
postdose observation period)c 
 
X 
 
 
 
 
 
One IM injection in the deltoid 
muscle 
Refer to Section 2.5.2.2 
Blood collection for humoral 
immunogenicity 
 
X 
 
X 
 
X 
 
Prior to study intervention dosing 
on Day 1 
NP swab for virus detectiond 
 
X 
 
 
 
 
X 
Prior to study intervention dosing 
on Day 1 
Refer to Section 2.8.3.4 and 
Section 2.8.3.11.3 
eDiary activation for 
recording solicited ARs 
(7 days)e 
 
X 
 
 
 
 
 
Refer to Section 2.8.3.6 
Review of solicited ARs 
eDiary 
 
X 
X 
 
 
 
 
 
Follow up safety callf 
 
 
X 
 
X 
 
 
Refer to Section 2.8.3.5 
Recording of unsolicited AEs 
 
X 
X 
X 
 
 
Xg 
Refer to Section 2.8.3.8 and 
Section 5.3 

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Visit Number 
 
1 
2 
3 
4 
5 
USV 
Notes 
Type of Visit 
C 
C 
SC 
C 
SC 
C 
C 
 
Month Timepoint 
 
 
 
M1 
M3 
M6 
Up to M6 
 
Visit Day  
Screeninga 
D1 
(Baseline) 
D8 
D29 
D91 
D181/ 
EoS 
N/A 
 
Window Allowance (Days) 
-28 
N/A 
+3 
-7 to +3 
±5 
±14 
N/A 
 
Recording of SAEs, AESIs, 
MAAEs, AEs leading to 
discontinuation from study 
participation, and concomitant 
medications/procedures 
relevant to or for their 
treatmenth 
 
X 
X 
X 
X 
X 
Xg 
 
Recording of concomitant 
medicationsi 
 
X 
X 
X 
 
 
 
Refer to Section 2.6.6.2 
Recording of concomitant 
procedures/surgeries 
 
X 
X 
X 
X 
X 
Xg 
Refer to Section 2.6.6.2 
Recording of non-study 
vaccinationsj 
 
X 
X 
X 
X 
X 
 
Refer to Section 2.6.6.2 
Study completion 
 
 
 
 
 
X 
 
 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; C = clinic/in-person visit; D = day; eDiary = electronic 
diary; EoS = end of study; ILI = influenza-like illness; IM = intramuscular(ly); M = month; MAAE = medically attended adverse event; N/A = not applicable; 
NP = nasopharyngeal; SAE = serious adverse event; SC = safety call (or contact by electronic means); USV = unscheduled visit. 
a. 
The Screening Visit and D1 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. 
b. 
Verbal medical history is acceptable. Clinically significant findings during the Screening Visit physical examination should also be recorded in the 
participant’s medical history. 
c. 
See Section 2.5.1, Table 3 for dose levels and treatment groups. 

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d. 
An NP swab specimen for viral respiratory pathogens will be collected prior to the study intervention dosing on D1. If a participant reports ILI symptoms 
within 7 days after symptom onset, an unscheduled visit for symptom assessment should occur. If the symptoms meet the criteria for protocol-defined ILI, an 
NP swab must be collected if it is within 7 days after ILI symptom onset. 
e. 
The eDiary entries will be recorded at approximately 30 minutes after study intervention dosing while at the clinic with instruction provided by the clinic 
staff. Study participants will continue to record in the eDiary for solicited ARs each day after they leave the clinic, on the day of study intervention dosing 
and the subsequent 6 days following study intervention dosing. 
f. 
An unscheduled follow-up safety call may be triggered if an eDiary record results in identification of a relevant safety event. A safety phone call may trigger 
an unscheduled visit. 
g. 
There may be situations in which the Investigator asks a participant to report for an unscheduled visit following the report of an AE. Additional examinations 
may be conducted at these visits as necessary to ensure the safety and well-being of participants during the study. 
h. 
Trained clinic staff will call (or contact by electronic means) all participants to collect information relating to any MAAEs, AEs leading to discontinuation 
from study participation, SAEs, AESIs, information on concomitant medications associated with those events, and any non-study vaccinations. 
i. 
All concomitant medications will be recorded from D1 through D29; thereafter, only concomitant medications relevant to or for the treatment of an SAE, 
AESI, or MAAE will be recorded through D181 (Month 6)/EoS. 
j. 
All non-study vaccinations will be recorded through 181 days after the dose of study intervention. 

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2.2. 
Objectives and Endpoints (Part A)  
The objectives which will be evaluated in this study and endpoints associated with each objective 
are provided in Table 2. 
Table 2: 
Objectives and Endpoints (Part A)  
Objectives 
Endpoints 
Primary 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed 
active comparator (Fluarix Quadrivalent) 
against 4 vaccine-matched influenza virus A 
and B strains at Day 29. 
• 
GMT at Day 29 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 29 as measured by 
HAI. 
• 
To evaluate the reactogenicity and safety of 
mRNA-1010. 
• 
Solicited local and systemic ARs through 
7 days after study intervention dosing. 
• 
Unsolicited AEs through 28 days after study 
intervention dosing. 
• 
MAAEs from Day 1 to Day 181/EoS. 
• 
AESI from Day 1 to Day 181/EoS. 
• 
SAEs from Day 1 to Day 181/EoS. 
• 
AEs leading to discontinuation from study 
participation from Day 1 to Day 181/EoS. 
Secondary 
• 
To further evaluate the humoral 
immunogenicity of mRNA-1010 against 4 
vaccine-matched influenza virus A and B 
strains at Day 29. 
• 
The proportion of participants with HAI titer 
≥1:40 at Day 29. 
• 
GMFR comparing Day 29 to Day 1 
(Baseline) as measured by HAI. 
Exploratory (May be Performed) 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed 
active comparator (Fluarix Quadrivalent) 
against 4 vaccine-matched influenza virus A 
and B strains at Day 181/EoS. 
• 
GMT at Day 181 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 181 as measured by 
HAI. 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed 
active comparator against vaccine-matched or 
vaccine-mismatched A and B strains, including 
the use of alternative methods. 
• 
GMT and GMFR of nAbs by assays such as 
MN assays or alternative methods against 
vaccine-matched or vaccine-mismatched 
strains on Day 29 compared with Day 1 
(Baseline). 
• 
GMT and GMFR of anti-HA antibodies as 
measured by HAI against vaccine-
mismatched strains on Day 29 compared 
with Day 1 (Baseline). 

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Objectives 
Endpoints 
• 
To assess the occurrence of clinical influenza 
in study participants and characterize their 
immune response to infection and viral 
isolates. 
• 
Frequency of RT-PCR-confirmed ILI and 
assessment of immune responses in 
participants with RT-PCR-confirmed ILI. 
Abbreviations: AE = adverse event; AESI = adverse events of special interest; AR = adverse reactions; EoS = end of 
study; GMFR = geometric mean fold rise; GMT = geometric mean titer; HA = hemagglutinin; 
HAI = hemagglutination inhibition; ILI = influenza-like illness; MAAE = medically attended adverse events; 
MN = microneutralization; mRNA = messenger ribonucleic acid; nAb = neutralizing antibody; RT-PCR = reverse 
transcription polymerase chain reaction; SAE = serious adverse event. 
2.3. 
Study Design (Part A)  
2.3.1. 
Overall Design (Part A)  
This is a Phase 3, randomized, stratified, observer-blind, active-controlled study to evaluate the 
immunogenicity, reactogenicity, and safety of mRNA-1010 seasonal influenza vaccine in adults 
18 years and older. 
mRNA-1010 to be tested contains 4 mRNAs in an equivalent mRNA mass ratio that encode 
membrane-bound HA of the 4 different influenza strains recommended by the WHO for 2022 to 
2023 NH cell- or recombinant-based vaccines. Fluarix Quadrivalent contains 4 HAs of the 4 
different influenza strains recommended by the WHO for 2022 to 2023 NH egg-based vaccines. 
Medically stable adults (see Part A Exclusion Criterion # 3), aged 18 years and older, will be 
screened and enrolled. A complete list of inclusion and exclusion criteria is provided in 
Section 2.4. 
Approximately 2400 participants will be randomly assigned (see Section 2.6) to treatment in this 
study in a 1:1: ratio to 1 of 2 treatment groups to receive either a single dose of mRNA-1010 or a 
single dose of a licensed seasonal influenza vaccine as an active comparator (Fluarix 
Quadrivalent, Table 3). 
Table 3: 
Treatment Groups and Dose Levels (Part A)  
Treatment 
Group 
Study Intervention 
Received 
mRNA/Antigen 
Total Dose 
(µg) 
Number of 
Participants 
HA (each) (µg) 
1 
mRNA-1010 
12.5 (of mRNA) 
50 (of 
mRNA) 
1200 
2 
Active Comparator 
(Fluarix Quadrivalent) 
15 (of protein) 
60 (of 
protein) 
1200 
Abbreviations: HA = hemagglutinin; mRNA = messenger ribonucleic acid 
Table 1 displays the study SoA. Clinic/in-person visits will consist of a Screening Visit (up to 28 
days before the Day 1 Visit and may be performed over multiple visits if within the 28-day 
screening window), a dosing visit on Day 1 (Baseline; may be on the same day as the Screening 
Visit), a visit on Day 29 (Month 1), and a subsequent visit on Day 181 (Month 6)/EoS with up to 
7 months of study participation for each participant. There will also be contacts by electronic 
means or telephone calls on Day 8 and Day 91 (Month 3). 

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All participants will provide blood samples for assessment of GMT, GMFR, and seroconversion, 
as measured by HAI (Table 1 and Section 2.8.2). There will be optional blood draws for future 
research (including genomics) and transcriptomics (Table 1, Section 2.8.6 and Section 2.8.7). 
An NP swab for viral respiratory panel testing will be collected at Baseline (Day 1) (prior to 
study intervention dosing) from all participants and at unscheduled clinic visits if participants 
have symptoms suggestive of ILI (Section 2.8.3.4). Table 1 displays the time periods for 
collecting solicited ARs via eDiary (Section 2.8.3.6) and unsolicited AEs. MAAEs, SAEs, and 
AESIs will be collected from Day 1 to Day 181 (Month 6)/EoS. 
There may be situations in which the Investigator asks a participant to report for an unscheduled 
visit following the report of an AE as shown in the SoA (Table 1). The eCRF should be 
completed for each unscheduled visit. 
This is an observer-blind study (refer to Section 2.6.1 for details). The Investigator may unblind 
in the event of an emergency (refer to Section 2.5.2.7 for details).  
An IST and CEAC will be involved (refer to Section 5.1.6 for details). 
2.3.2. 
Scientific Rationale for Study Design  
The study aims to demonstrate noninferiority of mRNA-1010 versus a licensed quadrivalent 
seasonal influenza vaccine (an active comparator) in the immune response for all 4 strains as 
measured by GMT and by seroconversion rate. 
The rationale for using HAI as a surrogate endpoint of prevention of influenza illness and its 
complications is based on the established precedent of using HA-based immunologic correlates 
for clinical assessment and licensure of influenza vaccines (DHHS 2007a, DHHS 2007b, 
Dunning et al 2016, European Medicines Agency 2016). 
2.3.3. 
Justification for Dose  
The Sponsor has completed a Phase 1/2 study of mRNA-1010 (mRNA-1010-P101, 
NCT04956575) at dose levels up to 200 µg and is now conducting three Phase 3 studies at a 
50 µg dose level: mRNA-1010-P301, a safety and immunogenicity study (NCT05415462), 
mRNA-1010-P302, a safety and efficacy study (NCT05566639), and an mRNA-1010-P303 
Part A (NCT05827978). No safety concerns were identified with dose levels up to 200 µg. The 
50-µg dose was chosen for the Phase 3 studies based on the observed reactogenicity and 
immunogenicity profile (refer to Section 1.2 for details). 
2.3.4. 
End of Study Definition  
The end of the study is defined as the date of the last visit of the last participant in the study or 
the last scheduled procedure for the last participant in the study. 
A participant is considered to have completed the study if the participant has completed all 
periods of the study including the last visit or last scheduled procedure.  
2.4. 
Study Population (Part A)  
Prospective approval of protocol deviations to recruitment and enrollment criteria, also known as 
protocol waivers or exemptions, is not permitted. 

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2.4.1. 
Inclusion Criteria (Part A)  
Participants are eligible to be included in the study only if all of the following criteria apply: 
Age 
1. At least 18 years of age inclusive, at the time of signing the ICF. 
Type of Participant and Disease Characteristics 
2. Investigator has assessed that the participant understands and is willing and 
physically able to comply with protocol mandated follow-up, including all 
procedures. 
Sex and Contraceptive/Barrier Requirements 
3. Participants AFAB are eligible to participate if they are not pregnant or 
breastfeeding/chestfeeding/bodyfeeding, and one of the following conditions applies: 
• Is a PONCBP as defined in Section 5.6. 
• Is a POCBP and using an acceptable contraceptive method as described in Section 5.6 
from at least 28 days before the dose of study intervention and during the study 
intervention period (at a minimum until 90 days after the dose of study intervention). 
The Investigator should evaluate the potential for contraceptive method failure (eg, 
noncompliance, recently initiated) in relationship to the dose of study intervention. 
• A POCBP must have a negative highly sensitive pregnancy test (urine or serum as 
required by local regulations) at the Screening Visit and before the dose of study 
intervention, if Day 1 is not on the same day as the Screening Visit (see 
Section 2.8.3.3). 
− If a urine test cannot be confirmed as negative (eg, an ambiguous result), a serum 
pregnancy test is required. In such cases, the participant must be excluded from 
participation if the serum pregnancy result is positive. 
• Additional requirements for pregnancy testing during and after study intervention are 
located in Section 2.8.3.3. 
• The Investigator is responsible for review of medical history, menstrual history, and 
recent sexual activity to decrease the risk for inclusion of a person with an early 
undetected pregnancy. 
Informed Consent 
4. Capable of giving signed informed consent as described in Section 5.1.3 which 
includes compliance with the requirements and restrictions listed in the ICF and in 
this protocol. 
2.4.2. 
Exclusion Criteria (Part A)  
Participants are excluded from the study if any of the following criteria apply: 

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Medical Conditions 
1. Acutely ill or febrile (temperature ≥38.0℃ [100.4°F]) within 72 hours prior to Day 1. 
Participants meeting this criterion may be rescheduled within the 28-day screening 
window. 
2. Close contact with someone with laboratory-confirmed influenza infection or with 
someone who has been treated with antiviral therapies for influenza (eg, Tamiflu®) 
within the past 5 days prior to Day 1. 
3. History of a diagnosis or condition that, in the judgment of the Investigator, is 
clinically unstable or may affect participant safety, assessment of safety endpoints, 
assessment of immune response, or adherence to study procedures. Clinically 
unstable is defined as a diagnosis or condition requiring significant changes in 
management or medication within the 60 days prior to Day 1 and includes ongoing 
workup of an undiagnosed illness that could lead to a new diagnosis or condition. 
• Asymptomatic conditions and conditions with no clinically significant end organ 
involvement (eg, mild hypertension, dyslipidemia) are not exclusionary, if they are 
being appropriately managed and are clinically stable (ie, unlikely to result in 
symptomatic illness within the time course of this study). Illnesses or conditions may 
be exclusionary, even if otherwise stable, due to therapies used to treat them (eg, 
immune-modifying treatments), at the discretion of the Investigator. 
• Participants who have undergone surgical procedures within 7 days prior to Day 1 or 
are scheduled to undergo a surgical procedure within 28 days after study intervention 
dosing are also excluded. However, minor surgical procedures under local anesthesia 
(eg, excision of skin lesion) or diagnostic procedures (eg, colonoscopy) are allowed. 
4. Reported history of congenital or acquired immunodeficiency, immunosuppressive 
condition or immune-mediated disease, asplenia, or recurrent severe infections. The 
following conditions are permitted at the discretion of the Investigator: 
• Participants who are HIV positive and on antiviral therapy with cluster of 
differentiation 4 count ≥350 cells/mm3 and HIV RNA ≤500 copies/mL within the past 
12 months. 
• Participants with immune-mediated diseases which are stable (eg, Hashimoto’s 
thyroiditis and type 1 diabetes) or conditions such as asthma, psoriasis, vitiligo, gout, 
alopecia areata, or auto-immune ovarian failure, which do not require systemic 
immunosuppressants per Part A Exclusion Criterion # 13. 
5. Dermatologic conditions that could affect local solicited AR assessments (eg, tattoos; 
psoriasis patches affecting skin over the deltoid areas). 
6. Participant has tested positive for influenza by local health authority-approved testing 
methods within 150 days prior to Day 1. 
7. Reported history of anaphylaxis or severe hypersensitivity reaction after receipt of 
mRNA vaccines or any components of the mRNA-1010 or influenza vaccines, including 
egg protein. 

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8. Reported history of coagulopathy or bleeding disorder that is considered a 
contraindication to IM injection or phlebotomy. 
9. Diagnosis of malignancy within the previous 2 years (excluding nonmelanoma skin 
cancer). 
10. History of myocarditis, pericarditis, or myopericarditis within onset of 180 days prior to 
Day 1 or have not returned to Baseline clinical status. Participants who have not returned 
to Baseline after their convalescent period will also be excluded. 
11. History of Guillain-Barre syndrome. 
12. Any medical, psychiatric, or occupational condition, including reported history of drug or 
alcohol abuse, that, in the opinion of the Investigator, might pose additional risk due to 
participation in the study or could interfere with the interpretation of study results. 
Prior/Concomitant Therapy 
13. Participant has received systemic immunosuppressants for >14 days in total within 
180 days prior to Day 1 (for corticosteroids, ≥10 mg/day of prednisone or equivalent) or 
is anticipating the need for systemic immunosuppressive treatment at any time during 
participation in the study. Inhaled, nasal, and topical steroids are allowed. Intra-articular 
and epidural steroid injections are not allowed within 28 days before and/or after study 
intervention dosing. 
14. Participant has received any vaccine authorized or approved by local health agency 
≤28 days prior to study intervention dosing (Day 1) or plans to receive a vaccine 
authorized or approved by local health agency within 28 days before or after study 
intervention dosing. 
15. Participant has received a licensed seasonal influenza vaccine within 5 months (150 days) 
prior to Day 1. 
16. Participant has participated in any investigational seasonal influenza vaccine study within 
12 months prior to Day 1. 
17. Participant is not aware whether they have received an influenza vaccine in the most 
recent influenza season (in the prior 12 months). 
18. Participant has been treated with antiviral therapies for influenza (eg, Tamiflu) within 
150 days prior to Day 1. 
19. Participant has received systemic immunoglobulins or blood products within 90 days 
prior to Day 1 or plans to receive systemic immunoglobulins or blood products during the 
study. In addition, participants who have received long-acting biological therapies that 
affect immune responses (eg, infliximab) within 90 days prior to Day 1, or plan to receive 
them, are also excluded. 
20. Participant has donated ≥450 mL of blood products within 28 days prior to Day 1 or 
plans to donate blood products during the study. 

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Other Exclusion Criteria 
21. Participant has participated in an interventional clinical study within 28 days prior to 
Day 1, based on the medical history interview or plans to do so while participating in this 
study. Participants may continue in prior interventional study follow-up activities, as long 
as it does not involve further investigational treatment other than the study intervention 
described in this protocol (Note: interventions such as counseling, biofeedback, and 
cognitive therapy are not exclusionary). 
22. Participant is working or has worked as study personnel or is an immediate family 
member or household member of study personnel, study site staff, or Sponsor personnel. 
2.4.3. 
Screen Failures  
A screen failure occurs when a participant who has consented to participate in the clinical study 
is not subsequently assigned to study intervention. 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 demography, screen failure details, eligibility criteria, 
and any SAE. 
Individuals who do not meet the criteria for participation in this study (screen failure) may be 
rescreened one time. 
2.4.4. 
Criteria for Temporarily Delaying the Day 1 Visit  
Body temperature (oral preferred) must be measured on the study intervention visit before 
dosing. The following events constitute criteria for delay of study intervention dosing, and if any 
of these events occur at the time scheduled for dosing, the participant may receive the study 
intervention dosing 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 2.7): 
• Acute moderate or severe infection with or without fever at the time of study 
intervention dosing. 
• Fever, defined as body temperature ≥38.0°C/≥100.4°F at the time of study 
intervention dosing. 
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 study intervention, the visit 
should be rescheduled within the allowed interval for that visit. 
2.5. 
Study Intervention(s) and Concomitant Therapy (Part A)  
Study intervention(s) refers to the mRNA-1010 vaccine (intervention label: mRNA-1010.6) and 
to the licensed seasonal influenza vaccine (the “active comparator”) intended to be administered 
to the study participants during the study conduct. 

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2.5.1. 
Study Intervention(s) Administered  
The study intervention(s) to be administered and the treatment groups in the study are provided 
in Table 4. 
The mRNA-1010 vaccine will be administered as a single 0.5 mL IM injection at an mRNA total 
dose level of 50 µg to participants according to the treatment group assignment. 
The active comparator administered in this study is a licensed quadrivalent seasonal influenza 
vaccine administered as a single 0.5 mL IM injection. 
Table 4: 
Study Intervention(s) Administered  
Intervention Label 
mRNA-1010.6 
Fluarix 
Treatment Group 
Type 
Experimental 
Active comparator 
Intervention Name 
mRNA-1010 
Fluarix Quadrivalent 
Intervention 
Description 
mRNA-1010 contains LNP dispersion 
encoding the seasonal influenza 
vaccine antigens, HAs, from the 
strains recommended by the WHO for 
2022 to 2023 NH cell- or 
recombinant-based vaccines. 
All mRNAs are formulated in LNPs 
composed of 4 lipids and provided as 
a sterile liquid for injection, white-to-
off white dispersion in appearance, at 
a concentration of 0.10 mg/mL in 
20 mM Tris buffer with 87 g/L 
sucrose, and 2.2 mM sodium acetate 
at pH 7.5. 
Licensed quadrivalent seasonal 
vaccine 
Fluarix Quadrivalent contains the 
seasonal influenza vaccine antigens, 
HAs, from the strains recommended 
by the WHO for 2022 to 2023 NH 
egg-based vaccines. 
Type 
Vaccine 
Vaccine 
Dosage Level(s) 
50 µg of mRNA 
Single dose 
60 µg of proteins 
Single dose  
Route of 
Administration 
IM 
IM 
Use 
Experimental 
Active control 

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Intervention Label 
mRNA-1010.6 
Fluarix 
IMP and AxMP 
IMP 
IMP 
Sourcing 
By Sponsor 
By Sponsor 
Packaging and 
Labeling 
The study intervention will be 
prepared, packaged, and labeled in 
accordance with the standard 
operating procedures of ModernaTX, 
Inc. or those of its designee, CFR 
Title 21, GMP guidelines, ICH and 
GCP guidelines, guidelines for 
Quality System Regulations, and 
applicable regulations. 
The study intervention will be 
prepared, packaged, and labeled in 
accordance with the standard 
operating procedures of ModernaTX, 
Inc. or those of its designee, CFR 
Title 21, GMP guidelines, ICH and 
GCP guidelines, guidelines for 
Quality System Regulations, and 
applicable regulations. 
Abbreviations: AxMP = auxiliary medicinal product; CFR = Code of Federal Regulations; GCP = Good Clinical 
Practice; GMP = Good Manufacturing Practice; HA = hemagglutinin; ICH = International Council for 
Harmonisation of Technical Requirements for Pharmaceuticals for Human Use; IM = intramuscular(ly); 
IMP = investigational medicinal product; LNP = lipid nanoparticle; mRNA = messenger ribonucleic acid; 
NH = Northern Hemisphere; WHO = World health Organization. 
2.5.2. 
Preparation, Handling, Storage, and Accountability  
The Investigator or designee must confirm appropriate conditions (eg, temperature) have been 
maintained during transit for all study intervention received, and any discrepancies are reported 
and resolved before use of the study intervention. 
Only participants enrolled in the study may receive study intervention, and only authorized clinic 
staff may supply, prepare, or administer study intervention. 
All study interventions must be stored in a secure, environmentally controlled, and monitored 
(manual or automated) area in accordance with the labeled storage conditions with access limited 
to the Investigator and authorized clinic staff. 
The Investigator is responsible for study intervention accountability, reconciliation, and record 
maintenance (ie, receipt, reconciliation, and final disposition records). 
Further guidance and information for the final disposition of unused study interventions are 
provided in the Pharmacy Manual. 
2.5.2.1. 
Study Intervention(s) Preparation  
The study intervention will be prepared for each participant based on their treatment group 
assignment. The mRNA-1010 vaccine will be administered as a single 0.5 mL IM injection and 
will contain mRNA-1010 at a dose of 50 µg. The active comparator will be administered at a 
volume of 0.5 mL. The mRNA-1010 and active comparator preparation instructions are detailed 
in the Pharmacy Manual. 
2.5.2.2. 
Study Intervention(s) Administration  
The study intervention (mRNA-1010 or the active comparator) will be administered as a single 
IM injection into the deltoid muscle on Day 1. Preferably, the study intervention should be 
administered into the nondominant arm. 

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Participants will be monitored for a minimum of 30 minutes after administration of the study 
intervention. Assessments will include vital sign measurements and monitoring for solicited ARs 
as shown in the SoA (Table 1). 
The clinic will be appropriately staffed with individuals with basic cardiopulmonary resuscitation 
training/certification. Either onsite resuscitation equipment and personnel or appropriate protocols for 
the rapid transport of a participant to a resuscitation area or facility are required. 
Further instructions for the preparation and administration of mRNA-1010 and active comparator 
are described in the Pharmacy Manual. 
2.5.2.3. 
Study Intervention(s) Packaging and Labeling  
The Sponsor will provide the Investigator (via the clinic pharmacy) with adequate quantities of 
the study intervention(s). The study intervention(s) will have all required labeling per regulations 
and will be supplied to the pharmacy in an unblinded manner. 
All study interventions used in this study will be prepared, packaged, and labeled in accordance 
with the standard operating procedures of the Sponsor or those of its designee, CFR Title 21, 
Good Manufacturing Practice guidelines, ICH, and GCP guidelines, guidelines for Quality 
System Regulations, and applicable regulations. 
2.5.2.4. 
Study Intervention(s) Storage  
mRNA-1010 must be stored at the clinical site at 2°C to 8°C in a secure area with limited access 
and must be protected from moisture and light until it is prepared for administration 
(Section 2.5.2.1). The refrigerator should have automated temperature recording and a 24-hour 
alert system in place that allows for rapid response in case of refrigerator malfunction. The 
refrigerator should be connected to a backup generator. In addition, for study intervention 
accountability, staff are required to keep a temperature log to establish a record of compliance 
with these storage conditions. The clinic is responsible for reporting any study intervention that 
was not temperature controlled during shipment or storage. Such study intervention will be 
retained for inspection by the monitor and disposed of according to approved methods. Please 
note that mRNA-1010 will be stored at -25°C to - 15°C at the depots and during shipments to the 
clinical sites. 
The active comparator should be stored in its original container and in accordance with the 
instructions in the Pharmacy Manual. 
2.5.2.5. 
Study Intervention(s) Accountability  
The Investigator is responsible for ensuring the study intervention accountability staff maintain 
an accurate record of the shipment receipt, the inventory at the site, dispensing of study 
intervention, and the return to the Sponsor or alternative disposition of used/unused study 
intervention in a study intervention accountability log. Study intervention accountability will be 
noted by the site monitor during site visits and at the completion of the study. For further 
direction, refer to the Pharmacy Manual. 

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2.5.2.6. 
Study Intervention(s) Handling and Disposal  
A site monitor will reconcile the study intervention during study conduct and at the end of the 
study for compliance. Once fully reconciled at the site, the study intervention can be destroyed at 
the investigational site or Sponsor selected third party, as appropriate. 
Study intervention may be destroyed at the clinic only if permitted by local regulations and 
authorized by the Sponsor. A Certificate of Destruction or equivalent must be obtained and sent 
to the Sponsor or designee. For further direction, refer to Pharmacy Manual. 
2.5.2.7. 
Unblinding  
Except in the case of medical necessity, a participant’s treatment assignment should not be 
unblinded without the approval of the Sponsor. If a participant becomes seriously ill or pregnant 
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 site monitor 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 unblinding’s will be tracked via an audit trail in IRT and 
documented in the final study report. 
2.6. 
Assignment to Study Intervention (Part A)  
Randomization will be performed using an IRT. Approximately 2400 participants will be 
randomly assigned to treatment in this study in a 1:1 ratio to 1 of 2 treatment groups to receive 
either a single dose of mRNA-1010 or a single dose of a licensed seasonal influenza vaccine as 
an active comparator (Fluarix Quadrivalent, Table 3). Randomization will be stratified by age 
categories (18 to <50 years old, ≥50 to <65 years old, or ≥65 years old) and influenza vaccine 
status in the prior 12 months (received or not received). Approximately 50% of participants 
(1200) enrolled will be ≥50 years old, including approximately 20% (480) who will be ≥65 years 
old. The Sponsor anticipates approximately 200 participants enrolled in the ≥65 years old age 
group will be ≥75 years old. 
2.6.1. 
Blinding  
As the appearance of the study interventions differ, enrollment will be observer blinded as to 
treatment assignment. 
Dose preparation, administration, and accountability of study intervention will be performed by 
designated unblinded clinic staff who will not participate in any of the clinical study evaluations. 
The unblinded clinic staff will prepare the study intervention out of view of the participant and 
the blinded clinic staff. 
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. 
Neither the participant nor the Investigator nor clinic staff responsible for study 
assessments/safety will have access to the treatment assignment during the conduct of the study. 

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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 intervention. Instructions regarding emergency unblinding will be provided 
to the Investigator and are discussed in Section 2.5.2.7. 
The Investigator, clinic staff, study participants, site monitors, and Sponsor personnel (or its 
designees) will be blinded to the study intervention administered until the study database is 
locked and unblinded for the final analysis. At the primary analysis (see Section 2.9.6), 
pre-identified Sponsor team members and selected CRO team members will be unblinded to 
conduct the analyses. Clinics will remain blinded. 
2.6.2. 
Study Intervention Compliance  
When participants are dosed at the site, they will receive study intervention directly from the 
Investigator or designee, under medical supervision. The date and time of the dose administered 
in the clinic will be recorded in the source documents. The dose of study intervention and study 
participant identification will be confirmed at the time of dosing by a member of the clinic staff 
other than the person administering the study intervention. 
2.6.3. 
Dose Modification  
Not applicable. 
2.6.4. 
Continued Access to Study Intervention After the End of the Study  
Continued access to the study intervention will not be available after the end of the study. 
2.6.5. 
Treatment of Overdose  
The study intervention will be provided in a single dose vial and is to be administered by a 
healthcare provider. It is unlikely that an overdose will occur. Should overdose occur, careful 
monitoring and follow-up must be performed. 
2.6.6. 
Prior and Concomitant Therapy  
Medications administered within the period starting 28 days before the study intervention must 
be recorded in the eCRF. 
2.6.6.1. 
Prohibited Therapy  
Medications prohibited for the duration of the study are: 
• Systemic immunosuppressive treatment (for corticosteroids, ≥10 mg/day of 
prednisone or equivalent). Intra-articular and epidural steroids are not allowed within 
28 days before and/or after study intervention dosing. Inhaled, nasal, and topical 
steroids are allowed. 
• Systemic immunoglobulins or blood products. 
• Long-acting biological therapies that affect immune responses (eg, infliximab). 

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The Investigator should contact the medical monitor with questions regarding potential 
prohibited medications and to determine eligibility for the study. It is the Investigator’s 
responsibility to ensure that details regarding the concomitant medications are adequately 
recorded in the eCRF. 
2.6.6.2. 
Recording of Concomitant Medications, Concomitant Vaccinations and 
Concomitant Procedures  
The following concomitant medication(s) and vaccine(s) must be recorded in the eCRF: 
• Any vaccine (authorized or investigational) administered in the prior 12 months. For 
authorized influenza vaccines, detailed information regarding which vaccine was 
administered should be provided if available. 
• All prohibited therapies (Section 2.6.6.1) at the time of the Day 1 Visit. 
• All concomitant medications taken at the time of the Day 1 Visit through 28 days 
after study intervention dosing. 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 non-study vaccines taken through 181 days after study intervention dosing. 
• Systemic steroids (≥10 mg/day prednisone or equivalent), immunosuppressants, 
immunoglobulins and long-acting biological therapies that affect immune responses 
(eg infliximab), and/or blood products administered at any time during the study 
period after the study intervention. 
• Any concomitant medications relevant to or for the treatment of an SAE, AESI, or 
MAAE from Day 1 through Day 181 (Month 6)/EoS. 
• The participant will be asked in the eDiary if they have taken any antipyretic or 
analgesic to treat or prevent fever or pain within 7 days after study intervention 
dosing, including the day of dosing. Reported antipyretic or analgesic medications 
should be recorded in the source document by the clinic staff during the clinic/in-
person visit and safety phone call after study intervention dosing or via other 
participant interactions (eg, telephone calls). 
• All concomitant procedures/surgeries at any time during the study period after study 
intervention dosing. 
Concomitant medications (including vaccinations) will be coded using the WHO Drug Global. 
2.6.6.3. 
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 evaluability in the PP analysis 
(analysis sets are described in Section 2.9.4): 
• Any investigational or nonregistered product (drug or vaccine) other than the study 
intervention used during the study period. 

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• Immunosuppressants administered chronically (ie, more than 14 days in total) during 
the study period. For corticosteroids, this will mean that prednisone ≥10 mg/day or 
the equivalent is not permitted. Intra-articular and epidural steroids are not allowed 
within 28 days before and/or after study intervention dosing. Inhaled, nasal, and 
topical steroids are allowed. 
• Long-acting, immune-modifying drugs administered at any time during the study 
period (eg, infliximab). 
• An authorized or licensed vaccine administered within 28 days of study intervention 
dosing. 
• Immunoglobulins and/or any blood products administered during the study period. 
2.7. 
Discontinuation of Study Intervention and Participant 
Discontinuation/Withdrawal (Part A)  
Discontinuation of specific sites or of the study as a whole are detailed in Section 5.1.10. 
2.7.1. 
Discontinuation of Study Intervention  
Not applicable. 
2.7.1.1. 
Participant Discontinuation/Withdrawal from the Study  
A participant may withdraw from the study at any time at the participant’s own request for any 
reason (or without providing any reason). 
A participant may be withdrawn at any time at the discretion of the Investigator for safety, 
behavioral, or compliance reasons. 
At the time of discontinuing from the study, if possible, the Investigator will request that the participant 
complete all study procedures pending at the time of withdrawal, as shown in the SoA (Table 1). 
The participant will be permanently discontinued from the study participation at that time. 
A participant who withdraws from the study will not be replaced. 
If the participant withdraws consent for disclosure of future information, the Sponsor may retain 
and continue to use any data collected before such a withdrawal of consent. 
If a participant withdraws from the study, the participant may request destruction of any samples 
taken and not tested, and the Investigator must document this in the site study records. 
The Sponsor will continue to retain and use all research results that have already been collected 
for the study evaluation. All biological samples that have already been collected may be retained 
and analyzed at a later date (or as permitted by local regulations). 
From an analysis perspective, a “withdrawal” from the study refers to a situation wherein a 
participant does not return for the final visit foreseen in the protocol. All data collected until the 
date of withdrawal or last contact of the participant will be used for the analysis. A participant is 
considered a “withdrawal” from the study when no study procedure has occurred, no follow up 
has been performed, and no further information has been collected for that participant from the 
date of withdrawal or last contact. 

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Information relative 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 a 
participant, or by the Investigator, as well as which of the following possible reasons was 
responsible for withdrawal: 
• Adverse event 
• Death 
• LTFU 
• Noncompliance with study procedures 
• Physician decision 
• Pregnancy 
• Protocol deviation 
• Study terminated by Sponsor 
• Withdrawal by participant 
• Withdrawal due to solicited AR/reactogenicity 
• Other 
Participants who are withdrawn from the study because of SAEs/AEs must be clearly 
distinguished from participants who are withdrawn for other reasons. Investigators will follow-
up with participants who are withdrawn from the study because of an SAE or AE until resolution 
of the event. 
2.7.1.2. 
Lost to Follow-up  
A participant will be considered LTFU if the participant repeatedly fails to return for scheduled 
visits 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 site must attempt to contact the participant and reschedule the missed visit as 
soon as possible, counsel the participant on the importance of maintaining the 
assigned visit schedule and ascertain whether the participant wishes to and/or should 
continue in the study. 
• Before a participant is deemed LTFU, the Investigator or designee must make every 
effort to regain contact with the participant (where possible, 3 telephone calls, and if 
necessary, a certified letter to the participant’s last known mailing address or local 
equivalent methods). These contact attempts (eg, dates of telephone calls and certified 
letter) should be documented in the participant’s medical record. 
• Should the participant continue to be unreachable, the participant will be considered 
to have withdrawn from the study. 
• A participant should be not considered LTFU until due diligence has been completed. 

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2.7.2. 
Pause Rules  
Not applicable. 
2.8. 
Study Assessments and Procedures (Part A)  
Study procedures and their timing are summarized in the SoA (Table 1). Protocol waivers or 
exemptions are not allowed. 
Adherence to the study design requirements, including those specified in the SoA (Table 1), is 
essential and required for study conduct. 
All screening evaluations must be completed and reviewed to confirm that potential participants 
meet all eligibility criteria (Section 2.4). The Investigator will maintain a screening log to record 
details of all participants screened and to confirm eligibility or record reasons for screening 
failure, as applicable. 
Procedures conducted as part of the participant’s routine clinical management (eg, blood count) 
and obtained before signing of the ICF may be utilized for Screening or Baseline purposes 
provided the procedures met the protocol-specified criteria and were performed within the 
timeframe defined in the SoA (Table 1). 
In the event of a significant study-continuity issue (eg, caused by a pandemic), alternate 
strategies for participant visits, assessments, medication distribution and monitoring may be 
implemented by the Sponsor or the Investigator, as per local health authority/ethics requirements. 
Study results that could unblind the study will not be reported to investigative sites or other 
blinded clinic staff until the study database is locked and unblinded. 
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. 
Sample collection on Day 1 (ie, blood and NP swab) must be performed prior to study 
intervention dosing. 
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. 
All study visits with the exception of the Screening Visit and Day 1 Visit can take place at the 
study site or mobile site or at the home of the participant, where allowed by local regulations, 
and upon written Sponsor approval. If a visit cannot be scheduled within the indicated allowable 
window and/or the participant misses the visit, this is considered a protocol deviation. However, 
the visit should still be completed, if possible, to collect study data. Subsequent visits should be 
scheduled at the originally planned number of days after Day 1 defined in the SoA (Table 1). 
2.8.1. 
Demography  
Demographic information relating to the participant’s sex, age, and race will be recorded at 
Screening in the eCRF. 
Medical history of each participant will be collected and recorded in the eCRF. Significant findings that 
were present prior to the signature of the informed consent will also be included in the eCRF. 

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2.8.2. 
Immunogenicity Assessments  
Planned timepoints for all immunogenicity assessments are provided in the SoA (Table 1). The 
following analytes will be measured: 
• Serum antibody level as measured by HAI assay. 
• Serum neutralizing antibody level as measured by microneutralization assay or 
similar methods may also be performed. 
Measurement of antibody levels will be performed in a laboratory designated by the Sponsor. 
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 influenza vaccines, 
additional assay development, and the immune response across influenza viruses. 
2.8.3. 
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 that occur during the 7 days following the study 
intervention dosing (ie, the day of study intervention dosing and 6 subsequent days). 
Solicited ARs will be recorded daily using an eDiary. 
• Unsolicited AEs observed or reported during the 28 days following the study 
intervention dosing (ie, the day of study intervention dosing and 27 subsequent days). 
Unsolicited AEs are AEs that are not included in the protocol defined solicited ARs. 
• AEs leading to discontinuation from study participation from Day 1 (poststudy 
intervention dosing) through Day 181 (Month 6)/EoS. 
• MAAEs from Day 1 through Day 181(Month 6)/EoS. 
• AESIs from Day 1 through Day 181 (Month 6)/EoS. 
• SAEs from Day 1 through Day 181 (Month 6)/EoS. 
• Details of pregnancies in participants may be collected after the start of study 
intervention dosing (see Section 2.8.3.8.5); however, pregnancy related data received 
after the end of the study may not be collected in the clinical database. 
• Vital sign measurements. 
• Physical examination findings. 
• Concomitant medications and non-study vaccinations. 
• Concomitant procedures. 
• Pregnancy testing. 
2.8.3.1. 
Physical Examinations  
A complete physical examination will be performed at the Screening Visit. A complete physical 
examination will include, at a minimum, assessments of skin, head, ears, eyes, nose, throat, neck, 

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thyroid, lungs, heart, cardiovascular system, abdomen, lymph nodes, and musculoskeletal system 
and extremities. Height and weight will also be measured and recorded. Any clinically 
significant finding identified during the Screening Visit should be reported as medical history. 
Symptom-directed physical examinations will be performed at other clinic/in-person visits, at the 
discretion of the Investigator, except at Screening where a full physical examination will be 
performed (Table 1). Any clinically significant finding identified during a symptom-directed 
physical examination should be reported as an AE. 
Investigators should pay special attention to clinical signs related to previous serious illnesses. 
2.8.3.2. 
Vital Signs  
Vital signs including systolic and diastolic blood pressures, pulse rate, respiratory rate, and body 
temperature will be measured at the timepoints indicated in the SoA (Table 1). Vital signs may 
be collected at other clinic/in-person visits in conjunction with a symptom-directed physical 
examination. The preferred route of temperature assessment is oral. 
The participant will be seated for at least 5 minutes before all measurements are taken. On 
Day 1, vital sign measurements will be collected once before study intervention dosing and at 
least 30 minutes after study intervention dosing (before participants are discharged from the 
study site). If vital signs are clinically concerning, participant should not be dosed. When 
applicable, vital sign measurements should be performed before blood collection. 
Febrile participants on the study intervention dosing day (fever is defined as a body temperature 
≥38.0°C/100.4°F) may be rescheduled within the relevant window periods. Criteria for delay of 
study intervention dosing are provided in Section 2.4.4. 
An abnormal vital sign measurement should be assessed to determine if it meets AE reporting 
criteria per protocol and reported as an AE in the EDC, if appropriate. The Investigator will 
continue to monitor the participant with additional assessments until the vital sign value has 
reached the reference range, returns to the vital sign value at Baseline, is considered stable, or 
until the Investigator determines that follow-up is no longer medically necessary. 
2.8.3.3. 
Pregnancy Testing  
Refer to Section 2.4.1 for pregnancy testing entry criteria and to Section 5.2 Appendix 2 for 
clinical laboratory tests. 
A pregnancy test either via blood or point-of-care urine test will be performed at the Screening 
Visit and before study intervention dosing if Day 1 is not on the same day as the Screening Visit. 
At the discretion of the Investigator, a pregnancy test either via blood or point-of-care urine can 
be performed at any time. The participant’s FSH level may be measured at the Screening Visit, 
as necessary and at the discretion of the Investigator, to confirm postmenopausal status. 
2.8.3.4. 
Assessments for Respiratory Viral Infections (Part A Only) 
NP swab specimen(s) for viral respiratory pathogens will be collected prior to study intervention 
dosing on Day 1. The participant will be instructed to contact the study site if they have 
symptoms suggestive of ILI throughout the study up to Day 181 (Month 6)/EoS. An unscheduled 
visit for symptom assessment and NP swab will be conducted if a participant reports protocol- 

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defined ILI that is within 7 days from symptom onset. Participants who manifest protocol-
defined ILI will be evaluated by RT-PCR testing of NP swab specimen(s) for influenza (and 
other respiratory pathogens) (Section 2.8.3.11.3). NP swabs may be collected as part of a home 
visit in lieu of a clinic/in-person visit, according to site procedures and prior Sponsor approval. 
In the event that NP swabs during ILI cannot be collected, any available influenza testing results 
performed outside of the study should be captured in the eCRF. 
2.8.3.5. 
Safety Phone Calls  
A safety phone call is a telephone call made to the participant by trained clinic staff. This call 
will follow a script, which will facilitate the collection of relevant safety information. Safety 
phone calls will follow a schedule for each participant, as shown in the SoA (Table 1). The 
participant will be interviewed according to the script about occurrence of AEs, MAAEs, SAEs, 
AESIs, AEs leading to discontinuation from study participation, concomitant medications 
associated with those events, and any non-study vaccinations. All safety information collected 
from the phone call must be documented in the source documents as described by the participant 
and not documented on the script used for the phone call. An unscheduled follow-up safety call 
may be triggered if an eDiary record results in identification of a relevant safety event. A safety 
phone call may trigger an unscheduled visit. 
2.8.3.6. 
Use of Electronic Diaries  
At the time of consent, the participants must confirm they will be willing to complete an eDiary 
(for 7-day reactogenicity). The local and systemic ARs that will be solicited by the eDiary are 
described in Table 16. 
Solicited local and systemic reactogenicity ARs will be collected on the day of study intervention 
dosing and during the 7 days after study intervention dosing (ie, the day of study intervention 
dosing and 6 subsequent days). Details on the recording of solicited local and systemic ARs are 
included in Section 2.8.3.9. 
At the dosing visit, participants will record data into the eDiary starting approximately 
30 minutes after study intervention dosing under supervision of the clinic staff to ensure 
successful entry of assessments. The 30-minute observation period is an opportunity for clinic 
staff to train the participant on eDiary completion requirements. The clinic staff will perform any 
retraining as necessary. 
At the dosing visit, participants will be instructed on thermometer usage to measure body 
temperature, ruler usage to measure injection site erythema (redness) and swelling/induration 
(hardness), and self-assessment for localized axillary (underarm) swelling or tenderness 
ipsilateral (on the same) side as the injection arm(s) during the 7 days after study intervention 
dosing. Daily oral temperature measurement should be performed at approximately the same 
time each day using the thermometer provided by the clinic staff. 
The participant will be trained on how to complete the eDiary questions according to the SoA 
(Table 1). If eDiary questions result in identification of relevant safety events according to the 
study period or symptoms, a follow-up safety call will be triggered. The results of the safety call 
should be recorded in the appropriate source documentation. 

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If a participant does not respond to the eDiary questions according to the SoA, clinic staff will 
follow-up with the participant. 
2.8.3.7. 
Ancillary Supplies for Participant Use  
Clinics will distribute Sponsor-provided oral thermometers and rulers for use by participants in 
assessing body temperature and injection site reactions, for recording solicited ARs in the 
eDiary. Based on availability, smartphone devices may be provided to those participants who do 
not have their own device to use for eDiary activities. 
2.8.3.8. 
AEs, SAEs, and Other Safety Reporting  
The definitions of AEs, SAEs, solicited ARs, and unsolicited AEs can be found in Section 5.3. 
The Investigator and any qualified designees are responsible for detecting, documenting, and 
recording events that meet the definition of an AE or SAE and remain responsible for following 
up all AEs. This includes events reported by the participant (or, when appropriate, by a 
caregiver, surrogate, or the participant’s legally authorized representative). 
The method of recording, evaluating, and assessing causality of AEs and SAEs and the 
procedures for completing and transmitting SAE reports are provided in Section 5.3. 
2.8.3.8.1. Time Period and Frequency for Collecting AE and SAE Information  
All SAEs, AESI, MAAE, and AEs leading to discontinuation from study participation will be 
collected from the start of study intervention dosing until Day 181 (Month 6)/EoS or withdrawal 
from the study at the timepoints specified in the SoA (Section 5.3). 
All solicited local and systemic ARs will be collected from the start of study intervention and 
during the 7 days following the study intervention (ie, the day of study intervention dosing and 
6 subsequent days). 
All unsolicited AEs will be collected from the start of study intervention and during the 28 days 
following the study intervention (ie, the day of study intervention and 27 subsequent days). 
Medical occurrences that begin before the start of study intervention but after obtaining informed 
consent will be recorded as medical history/current medical conditions, not as AEs; however, if 
the condition worsens at any time after study intervention administration, it will be recorded and 
reported as an AE. 
All SAEs will be recorded and reported to the Sponsor or designee immediately and under no 
circumstance should this exceed 24 hours of becoming aware of the event, as indicated in 
Section 5.3. The Investigator will submit any updated SAE data to the Sponsor within 24 hours 
of it being available. 
Investigators are not obligated to actively seek information on AEs or SAEs after the study 
completion Visit. However, if the Investigator learns of any SAE, including a death, at any time 
after a participant has been discharged from the study, and the Investigator considers the event to 
be reasonably related to the study intervention or study participation, the Investigator must 
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2.8.3.8.2. Method of Detecting AEs and SAEs  
An electronic diary has specifically been designed for this study by the Sponsor for collection of 
solicited adverse reactions (see Section 2.8.3.6). At the time of consent, the participants must 
confirm they will be willing to complete the eDiary via an application downloaded to their 
smartphone or via a device that is provided at the time of enrollment. Prior to enrollment on 
Day 1, the participant will be instructed to download the eDiary application or will be provided 
an eDiary device to record solicited ARs for 7 days (ie, the day of study intervention dosing and 
6 subsequent days). The diary will include prelisted ARs (solicited ARs) and intensity scales. 
At every clinic/in-person visit or telephone contact, participants will be asked a standard question 
to elicit any medically related changes in their well-being (including surveillance for respiratory 
viral infection symptoms) for detection of unsolicited AEs, according to the scripts provided. 
Participants will also be asked if they have been hospitalized, had any accidents, used any new 
medications, changed concomitant medication regimens (both prescription and over-the-counter 
medications), or had any non-study vaccinations. 
Detection of all AEs will be through 28 days after study intervention dosing (ie, the day of study 
intervention dosing and 27 subsequent days). Detecting MAAEs, AESI, SAEs, and AEs leading 
to discontinuation from study participation will continue through Day 181 (Month 6)/EoS 
(Table 1). 
The Investigator is responsible for the documentation of AEs regardless of treatment group or 
suspected causal relationship to the study intervention. 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 or AESI requiring immediate notification to 
the Sponsor or its designated representative. 
Care will be taken not to introduce bias when detecting AEs and/or SAEs. Open-ended and 
nonleading verbal questioning of the participant is the preferred method to inquire about AE 
occurrences. 
2.8.3.8.3. Follow-up of AEs and SAEs  
After the initial AE/SAE report, the Investigator is required to proactively follow each 
participant at subsequent visits/contacts. 
All SAEs and AESIs (as defined in Section 2.8.3.11) 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 2.7.1.2). Further information on the follow-up procedures is 
provided in Section 5.3. 
2.8.3.8.4. Regulatory Reporting Requirements for SAEs  
Prompt notification by the Investigator to the Sponsor of an SAE is essential so that legal 
obligations and ethical responsibilities toward the safety of participants and the safety of a study 
intervention under clinical investigation are met. 
The Sponsor has a legal responsibility to notify both the local regulatory authority and other 
regulatory agencies about the safety of a study intervention under clinical investigation. The 

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Sponsor will comply with country-specific regulatory requirements relating to safety reporting to 
the regulatory authority, IRBs, and investigators.  
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/ package insert and will notify the IRB, if appropriate according to local 
requirements. 
For expedited reporting purposes, the expectedness of SAEs will be assessed against the 
investigational treatment regimen the participant is receiving at the time of the event. AE terms 
not listed as expected events in the IB/package insert for investigational product(s) and 
comparator(s) will be considered unexpected. 
Investigator safety reports must be prepared for suspected unexpected serious adverse reactions 
according to local regulatory requirements and Sponsor policy and forwarded to investigators as 
necessary. 
2.8.3.8.5. Pregnancy  
The effects of mRNA-1010 on the unborn child and on the newborn baby are not known. 
Because of this, it is important that research study participants are not pregnant and do not 
become pregnant during the course of the research study. Pregnancy testing is scheduled to occur 
at the Screening Visit and Day 1 (Table 1). Individuals who have a positive pregnancy test at the 
Screening Visit must not be enrolled. Additional pregnancy testing may also be performed at any 
time during the study if required by local regulatory requirements, or at the discretion of the 
Investigator. 
The occurrence of pregnancy in participants will be collected after the start of study intervention 
and until Day 181 (Month 6)/EoS. If a pregnancy is reported, the Investigator will record 
pregnancy information on the form provided and submit it to the Sponsor within 24 hours of 
learning of the pregnancy. Participants who have a positive pregnancy test after receiving study 
intervention should remain in the study and be followed-up for safety. 
While pregnancy itself is not considered to be an AE or SAE, any pregnancy complication or 
elective termination of a pregnancy for medical reasons will be reported as an AE or SAE (refer 
to Section 5.3). Abnormal pregnancy outcomes (eg, spontaneous abortion, fetal death, stillbirth, 
congenital anomalies, ectopic pregnancy) are considered SAEs and will be reported as such 
(refer to Section 5.3). 
If pregnancy extends s beyond the participant’s EoS visit, follow-up with the participant by 
phone approximately one month after the estimated due date is expected. The Investigator will 
collect follow-up information on the pregnancy and its outcome on the form provided, and the 
information will be forwarded to the Sponsor. 
2.8.3.9. 
Solicited Adverse Reactions  
Solicited ARs are a subset of AEs consisting of selected signs and symptoms that participants are 
asked to record/report. In this study, the solicited ARs are reactogenicity events. The term 
“reactogenicity” refers to the occurrence of transient adverse effects associated with study 
intervention dosing. The eDiary will solicit daily participant reporting of ARs using a structured 

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checklist. Participants will record such occurrences in the eDiary on the day of study intervention 
dosing and 6 subsequent days. 
Severity grading of reactogenicity will occur automatically based on participant entry into the 
eDiary according to the grading scales presented Section 5.3, which are modified from the 
Toxicity Grading Scales for Healthy Adult and Adolescent Volunteers Enrolled in Preventive 
Vaccine Clinical Trials (DHHS 2007b). All solicited ARs (local and systemic) will be considered 
causally related to dosing. 
If a participant reports a solicited AR with onset during the solicited period, but they did not 
record the event in the eDiary, then the event should be recorded by study staff in EDC. 
If the event starts during the solicited period, but continues beyond 7 days after dosing, the 
participants should notify the site to provide an end date and close out the event in EDC, where 
reactogenicity is collected. 
If the participant reported an event that started after the solicited period (ie, beyond 7 days after 
dosing), it should be recorded as an AE in EDC. Causality for these events will be determined 
per assessment by the Investigator. 
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 clinic staff in EDC, where reactogenicity is collected: 
• Solicited local or systemic AR that results in a visit to a healthcare practitioner 
(medically attended AE). 
• Solicited local or systemic AR lasting beyond 7 days poststudy intervention dosing. 
• Solicited local or systemic AR that leads to participant discontinuation from study 
participation. 
• Solicited local or systemic AR that otherwise meets the definition of an SAE. 
2.8.3.10. Medically Attended Adverse Events  
The definition of MAAE is provided in Section 5.3.3. 
2.8.3.11. Adverse Events of Special Interest  
The definition of AESI is provided in Section 5.3.4. AESIs for this protocol are listed in 
Section 5.3. 
2.8.3.11.1. Anaphylaxis  
All suspected cases of anaphylaxis associated with study intervention dosing should be recorded 
as AESIs and reported as an SAE (Section 5.3 [Reporting of SAEs]), based on criteria for a 
medically important event, unless the event meets other serious criteria. For reporting purposes, a 
participant who displays signs/symptoms consistent with anaphylaxis as shown below should be 
reported as a potential case of anaphylaxis. This is provided as general guidance for investigators 
and is based on the Brighton Collaboration case definition (Rüggeberg et al 2007). 
Anaphylaxis is an acute hypersensitive reaction with multi-organ system involvement that can 
present as, or rapidly progress to, a severe life-threatening reaction. It may occur following 

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exposure to allergens from a variety of sources. Anaphylaxis is a clinical syndrome characterized 
by the following: 
• Sudden onset AND 
• Rapid progression of signs and symptoms AND 
• Involving 2 or more organ systems, as follows: 
− Skin/mucosal: urticaria (hives), generalized erythema, angioedema, generalized 
pruritus with skin rash, generalized prickle sensation, red and itchy eyes. 
− Cardiovascular: measured hypotension, clinical diagnosis of uncompensated 
shock, loss of consciousness or decreased level of consciousness, evidence of 
reduced peripheral circulation. 
− Respiratory: bilateral wheeze (bronchospasm), difficulty breathing, stridor, upper 
airway swelling (lip, tongue, throat, uvula, or larynx), respiratory distress, 
persistent dry cough, hoarse voice, sensation of throat closure, sneezing, 
rhinorrhea. 
− Gastrointestinal: diarrhea, abdominal pain, nausea, vomiting. 
2.8.3.11.2. Myocarditis and/or Pericarditis  
A case of suspected, probable, or confirmed myocarditis, pericarditis, or myopericarditis should 
be reported as an AESI, even if it does not meet criteria per the CDC case definition. The event 
should also be reported as an SAE if it meets seriousness criteria (see Section 5.3.2). 
An independent CEAC will review all suspected cases of myocarditis, pericarditis, and 
myopericarditis, which are reported in ongoing interventional clinical trials per the CEAC 
charter, to determine if they meet CDC criteria for “probable” or “confirmed” events 
(Section 5.1.6.2). 
The CDC Working Case Definitions are provided in Section 5.5 as guidance. 
2.8.3.11.3. Influenza-like Illness Case Definitions  
Protocol-defined ILI 
A protocol-defined ILI is determined by the occurrence of at least 1 respiratory illness symptom 
concurrently with at least 1 systemic symptom, or the occurrence of any 2 or more respiratory 
symptoms, as shown in Table 5. 

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Table 5: 
Respiratory and Systemic Symptoms for Protocol-defined Influenza-like 
Illness  
Respiratory symptoms 
Systemic symptoms 
1. Sore throat 
2. Cough/rhinorrhea/nasal congestion (≥1 of 
the 3 symptoms count as 1 respiratory 
symptom) 
3. Sputum production 
4. Wheezing 
5. Difficulty breathing 
1. Body temperature ≥37.5°C (≥99.5°F) 
2. Chills 
3. Tiredness 
4. Headache 
5. Myalgia 
6. Nausea/vomiting 
7. Diarrhea  
RT-PCR-confirmed Influenza Infection 
An RT-PCR-confirmed influenza infection is defined as a positive influenza result on a 
respiratory sample by RT-PCR within 7 days of onset of protocol-defined ILI performed at any 
setting during the study period. 
2.8.4. 
Pharmacokinetics  
Pharmacokinetic parameters are not evaluated in this study. 
2.8.5. 
Pharmacodynamics  
Pharmacodynamic parameters are not evaluated in this study. 
2.8.6. 
Genetics  
A prospective research sample(s), to be used for future genomic research, will be collected from 
participants who have consented to participate in the genomic analysis component of the study. 
Participation is optional. Participants who do not wish to participate in the genomic research may 
still participate in the study. 
2.8.7. 
Biomarkers  
Biomarkers may be evaluated for safety and/or vaccine efficacy using left over samples that 
include serum collections and NP swab. Transcriptomics may be evaluated as an optional 
assessment from participants that consent to providing the samples. Participants who do not wish 
to have their samples analyzed for transcriptomics may still participate in the study. 
2.8.8. 
Immunogenicity Assessments  
Antibodies to the study intervention will be evaluated in serum samples collected from all 
participants according to the SoA (Table 1). These samples will be tested by the Sponsor or 
Sponsor’s designee. 
The detection and characterization of antibodies to the study intervention will be performed 
using a validated assay method by or under the supervision of the Sponsor. All samples collected 
for detection of antibodies to the study intervention will also be evaluated for study intervention 
serum concentration to enable interpretation of the antibody data. Antibodies may be further 

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characterized and/or evaluated for their ability to neutralize the activity of the study 
intervention(s). Samples may be stored for the time period specified in the ICF (or according to 
local regulations) following the last participant’s last visit for the study at a facility selected by 
the Sponsor to enable further analysis of immune responses to the study intervention. 
2.8.9. 
Health Economics or Medical Resource Utilization and Health Economics  
Health economics or medical resource utilization and health economics parameters are not 
evaluated in this study. 
2.9. 
Statistical Considerations (Part A)  
This section summarizes the planned statistical analysis strategy and procedures for the study. 
The details of the statistical analyses will be provided in the SAP, which will be finalized before 
the clinical database lock for the study and treatment unblinding. If, after the study has begun, 
but prior to any unblinding, changes are made to primary and/or key secondary 
objectives/hypotheses, or the statistical methods related to those hypotheses, 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. 
2.9.1. 
Blinding and Responsibility for Analyses  
This is an observer-blind study. The investigators, clinic staff, study participants, site monitors, 
and Sponsor personnel (or its designees) will be blinded to the study intervention administered 
until the study database is locked and unblinded, with the following exceptions: 
• Unblinded personnel (of limited numbers) will be assigned to study intervention 
accountability procedures and will prepare the study intervention for all participants. 
These personnel will have no study functions other than study intervention 
management, documentation, accountability, preparation, and administration. They 
will not be involved in participant evaluations and will not reveal the identity of the 
study intervention to either the participants or the blinded clinic staff involved in the 
conduct of the study unless this information is necessary in the case of an emergency. 
• Unblinded clinic staff will administer the study intervention. They will not be 
involved in assessments of any study endpoints. 
• Unblinded site monitors, not involved in other aspects of monitoring, will be assigned 
as the study intervention accountability monitors. They will have responsibilities to 
ensure that sites are following all proper study intervention accountability, 
preparation, and administration procedures. 
• An independent unblinded statistical and programming team will perform the 
preplanned primary analysis (see Section 2.9.6). Sponsor team members will be 
prespecified to be unblinded to the primary analysis and will not communicate the 
results to the blinded investigators, clinic staff, clinical monitors, or participants. 

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• The IST may review data, as appropriate, to safeguard the interests of participants and 
to help ensure the integrity of the study. 
The dosing assignment will be concealed by having the unblinded pharmacy personnel prepare 
the study intervention in a secure location that is not accessible or visible to other clinic staff. An 
opaque sleeve over the syringe used for study intervention dosing will maintain the blind at the 
time of study intervention dosing, as the doses containing mRNA-1010 will look different from 
those of active comparator. Only delegated unblinded clinic staff will conduct the study 
intervention dosing procedure. Once the study intervention dosing is completed, only the blinded 
clinic staff will perform further assessments and interact with the participants. Access to the 
randomization code will be strictly controlled at the pharmacy. 
Procedures for breaking the blind in the case of a medical emergency are provided in 
Section 2.5.2.7. 
2.9.2. 
Statistical Hypotheses  
The null hypothesis H0: immunogenicity response to mRNA-1010, as measured by GMT and 
seroconversion rate at Day 29 using HAI assay, is inferior compared to that in participants who 
received the active comparator for each of the 4 vaccine-matched influenza virus A and B 
strains. 
Each of the 8 coprimary immunogenicity endpoints will be evaluated for noninferiority of 
mRNA-1010 versus the active comparator at a 2-sided alpha of 0.05 level. The study is 
considered as a success if all the 8 coprimary immunogenicity endpoints meet the noninferiority 
criteria. 
• For each of the 4 vaccine-matched strains, the noninferiority in GMT in participants 
who received mRNA-1010 compared to that of participants who received the active 
comparator will be demonstrated by the lower bound of the 95% CI of the GMR 
ruling out 0.667 (lower bound >0.667) using a noninferiority margin of 1.5. The 
GMR is the ratio of the GMT of HAI titer in those receiving mRNA-1010 compared 
with the GMT of those receiving the active comparator. 
• For each of the 4 vaccine-matched strains, the noninferiority in seroconversion rate in 
the mRNA-1010 group compared to that of the active comparator group will be 
demonstrated by the lower bound of the 95% CI of the seroconversion rate difference 
(mRNA-1010 versus the active comparator) ruling out -10% (lower bound >-10%) 
using a noninferiority margin of 10%. 
2.9.3. 
Sample Size Determination  
Assuming approximately 15% of 2400 randomized participants will be excluded from the PP 
Immunogenicity Set, with approximately 2040 participants in the PP Immunogenicity Set 
(1:1 ratio; approximately 1020 participants in each treatment group), the study has at least 98% 
power to demonstrate noninferiority of the immune response for all 4 strains, as measured by the 
GMT in participants receiving mRNA-1010 compared with that in the active comparator group, 
at a 2-sided alpha of 0.05 level, assuming an underlying GMR of 0.9 in all 4 strains and a 
noninferiority margin of 1.5. The standard deviation of the natural log-transformed levels is 
assumed to be 1.5. 

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The study has at least 95% power to demonstrate noninferiority of the immune response in all 
4 strains, as measured by seroconversion rate in the mRNA-1010 group compared with that in 
the active comparator group, at a 2-sided alpha of 0.05 level, assuming a seroconversion rate of 
69% in influenza A strains and 59% in influenza B strains, respectively, in the mRNA-1010 
group (a true rate difference is -1% compared to the active comparator group), and a 
noninferiority margin of 10%. 
The overall power considering meeting the primary objective to evaluate the immune response 
for all the 4 influenza virus strains is approximately 93%. 
2.9.4. 
Analysis Sets  
The analysis sets are defined in Table 6. 
Table 6: 
Populations for Analysis  
Population 
Description 
Randomization Set 
All participants who are randomly assigned to the treatment, 
regardless of the participants’ treatment status in the study. 
Full Analysis Set 
All participants in Randomization Set who received any study 
vaccination. 
Participants will be analyzed according to the group to which they 
were randomized. 
Immunogenicity Set 
All participants in the FAS who have Baseline and Day 29 antibody 
assessment via HAI assay. 
Participants will be analyzed according to the treatment group to 
which they were randomized. 
PP Immunogenicity Set 
The PP Immunogenicity Set includes all participants in the 
Immunogenicity Set who received the planned dose of study 
intervention, complied with the immunogenicity testing schedule for 
Baseline and Day 29, and had no major protocol deviations that 
impact key or critical data. Participants with RT-PCR-confirmed 
influenza between Days 1 to 29 will be removed from the PP 
Immunogenicity Set (Part A only). 
The PP Immunogenicity Set will be used for all analyses of 
immunogenicity unless otherwise specified. Participants will be 
analyzed according to the treatment group to which they were 
randomized. 
Solicited Safety Set 
All participants in the FAS who contributed any solicited AR data. 
The Solicited Safety Set will be used for the analyses of solicited 
ARs, and participants will be included in the treatment group 
corresponding to the study intervention that they actually received. 
Safety Set 
All participants in the FAS. 
The Safety Set will be used for all analyses of safety except for the 
solicited ARs. Participants will be included in the treatment group 
corresponding to the study intervention that they actually received. 
Abbreviations: AR = adverse reaction; FAS = Full Analysis Set; HAI = hemagglutination inhibition; 
PP = per-protocol; RT-PCR = reverse transcription polymerase chain reaction. 

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2.9.5. 
Statistical Analyses  
The SAP will be developed and finalized before database lock and will describe the preplanned 
statistical analysis details/data derivations, the participant populations to be included in the 
analyses, and procedures for accounting for missing and/or unused data. 
This section is a summary of the planned statistical analyses of the primary and secondary 
endpoints. 
2.9.5.1. 
Immunogenicity Analyses  
The primary analysis population for immunogenicity will be the PP Immunogenicity Set, unless 
otherwise specified. The primary objective of this study is to use the immunogenicity response to 
infer efficacy in participants receiving mRNA-1010. 
Immune responses, as measured by GMT and seroconversion rate in the mRNA-1010 group 
based on Day 29 HAI titers, will be compared to that in participants receiving the active 
comparator for all 4 strains. 
Rate of seroconversion is defined as the proportion of participants with either a prevaccination 
HAI titer <1:10 and a postvaccination titer ≥1:40 or a prevaccination HAI titer ≥1:10 and a 
minimum 4-fold rise in postvaccination HAI antibody titer. 
An ANCOVA model will be carried out. The model will include the log-transformed HAI titers 
at Day 29 as the dependent variable, treatment group as the fixed variable, log-transformed 
baseline HAI titers as a fixed covariate, adjusting for the stratification factors. The GLSM and its 
corresponding 95% CI results in log-transformed scale estimated from the model will be back-
transformed to obtain these estimates in the original scale, as an estimate of the GMT. GMR, 
estimated by the ratio of GLSM and the corresponding 2-sided 95% CI will be provided to assess 
the treatment difference. The corresponding 2-sided 95% CI of GMR will be provided to assess 
the difference in immune response between the mRNA-1010 group compared to the active 
comparator group at Day 29. For each strain, the noninferiority of GMT will be considered 
demonstrated if the lower bound of the 95% CI of the GMR is >0.667 based on a noninferiority 
margin of 1.5. 
The number and percentage of participants with seroconversion at Day 29 will be provided with 
2-sided 95% CI using the Clopper-Pearson method. To compare the seroconversion rates 
between the treatment groups, the Miettinen-Nurminen’s method will be used to calculate the 
95% CI for the difference in seroconversion rates. The difference in seroconversion rate at Day 
29 with the corresponding 95% CI will be provided. For each strain, the noninferiority of 
seroconversion rate will be considered demonstrated if the lower bound of the 95% CI of the 
seroconversion rate difference is >-10% based on a noninferiority margin of 10%. 
The primary analyses will be repeated using the Immunogenicity Set as a supplementary 
analysis. 
Subgroup analysis for the coprimary immunogenicity endpoints will be conducted as 
appropriate. 
In addition, the GMT of HAI titers with corresponding 95% CI will be provided at each 
timepoint. The 95% CIs will be calculated based on the t-distribution of the log-transformed 
values then back-transformed to the original scale. The GMFR of HAI titers with corresponding 

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95% CI at each postbaseline timepoint over baseline will be provided. Descriptive summary 
statistics including median, minimum, and maximum will also be provided. 
The number and percentage of participants with a HAI titer ≥1:40 postvaccination will be 
provided with 2-sided 95% CI using the Clopper-Pearson method. 
2.9.5.2. 
Adverse Events  
All safety analyses will be based on the Safety Set, except summaries of solicited ARs, which 
will be based on the Solicited Safety Set. All safety analyses will be provided by treatment 
group, unless otherwise specified. 
Safety and reactogenicity will be assessed by clinical review of all relevant parameters, including 
solicited ARs (local and systemic ARs), unsolicited AEs (including any clinical safety laboratory 
abnormalities), treatment-related AEs, severe AEs, SAEs, MAAEs, AEs leading to 
discontinuation from study participation, AESIs, vital sign measurements, and physical 
examination findings. 
The number and percentage of participants with any solicited local AR or solicited systemic AR 
during the 7-day follow-up period after study intervention dosing will be summarized. A 2-sided 
95% 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, treatment-related AEs, severe 
AEs, SAEs, AESIs, MAAEs, and AEs leading to discontinuation from study participation will be 
summarized. Unsolicited AEs will be coded according to the MedDRA and presented by 
MedDRA system organ class and preferred term. 
Solicited ARs will be coded according to the MedDRA for AR terminology. The Toxicity 
Grading Scales for Healthy Adult and Adolescent Volunteers Enrolled in Preventive Vaccine 
Clinical Trials will be used in this study (DHHS 2007b). 
The number of events of unsolicited AEs/SAEs, AESIs, MAAEs, and AEs leading to 
discontinuation from study participation will be reported in summary tables accordingly. For all 
other safety parameters, descriptive summary statistics will be provided. Further details will be 
described in the SAP. 
2.9.5.3. 
Exploratory Analyses  
Number and percentage of participants with RT-PCR confirmed influenza infection within the 
period of 14 days postinjection up to EoS and within the period of Day 1 up to EoS will be 
summarized for the Safety Set. A 2-sided 95% CI using the Clopper-Pearson method will be 
provided for the percentage of participants with the RT-PCR confirmed influenza infection. 
Exploratory analyses not addressed in Section 2.9.5.3 will be described in the SAP before 
database lock. 

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2.9.6. 
Planned Analyses  
2.9.6.1. 
Primary Analyses  
The primary analysis of safety and immunogenicity will be performed after all participants in 
Part A have completed the Day 29 visit. All data relevant to the primary study analysis through 
the Day 29 visit will be cleaned for the primary analysis (ie, data that are as clean as possible) 
and a report may be generated. 
The analysis will be performed by a separate team of unblinded programmers and statisticians. 
More details can be found in the study data blinding plan. 
2.9.6.2. 
Final Analysis  
Final analysis of all safety and immunogenicity data for Part A will be performed once all 
participants in Part A complete the Day 181 (Month 6)/EoS Visit. 
2.9.7. 
Multiplicity  
No multiplicity adjustment will be applied because the study is considered as a success only if all 
the 8 coprimary immunogenicity endpoints meet the noninferiority criterion. Each of the 
coprimary immunogenicity endpoints will be tested at 2-sided alpha of 0.05 level. 

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3. 
PART B  
3.1. 
Protocol Summary  
3.1.1. 
Synopsis (Part B)  
Rationale:  
The Sponsor is conducting Part B of this Phase 3 study, mRNA-1010-P303, to further evaluate 
its candidate seasonal influenza mRNA vaccine (mRNA-1010) compared to a SD seasonal 
influenza vaccine in adults 18 to <65 years old, to establish immunogenicity and obtain 
additional safety data in support of licensure. The design of this study will include 
immunogenicity objectives for HAI, a surrogate endpoint of prevention of influenza illness and 
its complications. The rationale for this approach is based on the established precedent of using 
HA-based immunologic correlates for clinical assessment and licensure of influenza vaccines 
(DHHS 2007a, DHHS 2007b, Dunning et al 2016, European Medicines Agency 2016). 
Objectives and Endpoints: 
Objectives 
Endpoints 
Primary 
• 
To evaluate the humoral immunogenicity 
(for noninferiority) of mRNA-1010 relative 
to that of a licensed SD seasonal influenza 
vaccine (Fluarix Quadrivalent) against 
4 vaccine-matched influenza virus A and B 
strains at Day 29 in adults 18 to <65 years 
old. 
• 
GMT at Day 29 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 29 as measured by HAI. 
• 
To evaluate the safety, including 
reactogenicity, of mRNA-1010. 
• 
Frequency and severity of solicited local and 
systemic ARs during a 7-day follow-up period 
postinjection. 
• 
Frequency and severity of any unsolicited AEs 
during the 28-day follow-up period 
postinjection. 
• 
Frequency of any SAEs, MAAEs, AESIs, and 
AEs leading to discontinuation from Day 1 to 
Day 181/EoS. 
Secondary 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 (for superiority) relative to a 
licensed SD seasonal influenza vaccine 
(Fluarix Quadrivalent) against vaccine-
matched influenza A and B strains at 
Day 29. 
• 
GMT at Day 29 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 29 as measured by HAI. 

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Objectives 
Endpoints 
• 
To evaluate the humoral immunogenicity of 
each study arm against vaccine-matched 
influenza A and B strains at Day 29  
• 
The proportion of participants with HAI titer 
≥1:40 at Day 29. 
• 
GMFR comparing Day 29 to Day 1 (Baseline) 
as measured by HAI. 
Exploratory (May be Performed) 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed SD 
seasonal influenza vaccine (Fluarix 
Quadrivalent) against vaccine-matched 
influenza virus A and B strains at 
Day 181/EoS in a subset of participants. 
• 
GMT at Day 181 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 181 as measured by 
HAI. 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed SD 
seasonal influenza vaccine (Fluarix 
Quadrivalent) against vaccine-matched or 
vaccine-mismatched A and B strains. 
• 
GMT and GMFR of nAbs by assays such as 
MN assays or alternative methods against 
vaccine-matched/mismatched strains on Day 
29 compared with Day 1 (Baseline). 
• 
GMT and GMFR of anti-HA antibodies as 
measured by HAI against vaccine-mismatched 
strains on Day 29 compared with Day 1 
(Baseline). 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; EoS = end of 
study; GMFR = geometric mean fold rise; GMT = geometric mean titer; HA = hemagglutinin; 
HAI = hemagglutination inhibition; MAAE = medically attended adverse event; MN = microneutralization; 
mRNA = messenger ribonucleic acid; nAb = neutralizing antibody; SAE = serious adverse event; SD = standard dose 
Overall Design Synopsis: 
mRNA-1010-P303 Part B is a Phase 3, randomized, stratified, observer-blind, active-controlled 
study to evaluate the immunogenicity, reactogenicity, and safety of mRNA-1010 seasonal 
influenza vaccine in adults 18 to <65 years old. 
Approximately 3000 medically stable adults 18 to <65 years of age, at the time of signing the 
ICF, will be randomly assigned to treatment in this study in a 1:1: ratio to 1 of 2 treatment groups 
to receive either a single dose of mRNA-1010 or a single dose of a licensed SD seasonal 
influenza vaccine (Fluarix Quadrivalent) at Day 1. Randomization will be stratified by the 
previous flu season (since September 2022) vaccination status (received or not received; if 
received, was it from prior participation in the mRNA-1010-P302 study [yes/no]). 
Brief Summary: 
The study aims to demonstrate noninferiority of mRNA-1010 versus a licensed SD seasonal 
influenza vaccine (Fluarix Quadrivalent) in the immune response, as measured by GMT and 
seroconversion rate at Day 29, using HAI assay, for each of the 4 vaccine-matched influenza 
virus A and B strains.  
Study details include: 
• There will be 3 to 4 clinic/in-person visits (Screening Visit and at Days 1, 29, and 
Day 181 [Month 6]/EoS [in a subset of ~ 1000 participants]) and 2 to 3 safety phone 

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call at Days 8, 91, and 181 (non-subset participants) as specified in the SoA. The 
Screening Visit and Day 1 may be performed on the same day or a different day. 
• All participants will be asked to complete an eDiary for solicited ARs for 7 days (ie, 
the day of study intervention dosing and 6 subsequent days). 
• Detection of all AEs will be through 28 days after study intervention dosing (ie, the 
day of study intervention dosing and 27 subsequent days). Detecting MAAEs, AESI, 
SAEs, and AEs leading to discontinuation from study participation will continue 
through Day 181 (Month 6)/EoS. 
Number of Participants: Approximately 3000 participants will be enrolled in Part B. 
Study Arms and Duration: 
• The study will comprise 2 study arms: investigational vaccine (mRNA-1010) group 
and licensed SD seasonal influenza vaccine (Fluarix Quadrivalent) group. 
• The total study duration (including screening) for each participant is up to 7 months. 

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3.1.2. 
SoA (Part B)  
Table 7: 
Schedule of Activities (Part B)  
Visit Number 
 
1 
2 
3 
4 
5 
Notes 
Type of Visit 
C 
C 
SC 
C 
SC 
SC/C 
 
Month Timepoint 
 
 
 
M1 
M3 
M6 
 
Visit Day  
Screeninga 
D1 
(Baseline) 
D8 
D29 
D91 
D181/ 
EoS 
 
Window Allowance (Days) 
-28 
N/A 
+3 
-7 to +3 
±5 
±14 
 
Informed consent form, demographics, 
concomitant medications, medical 
historyb 
X 
 
 
 
 
 
 
Inclusion/exclusion criteria 
X 
X 
 
 
 
 
Refer to Section 3.4.1 and 
Section 3.4.2 
Physical examinationb 
X 
 
 
 
 
 
Refer to Section 3.8.3.1 
Vital signs measurements 
X 
X 
 
 
 
 
Refer to Section 3.8.3.2 
Pregnancy testing 
X 
X 
 
 
 
 
Prior to study intervention dosing on 
Day 1 
Refer to Section 3.8.3.3 
Randomization 
 
X 
 
 
 
 
Refer to Section 3.6 
Blood collection for humoral 
immunogenicity 
 
X 
 
X 
 
Xi 
Prior to study intervention dosing on 
Day 1 
Study intervention dosing (including 30-
minute, postdose observation period)c 
 
X 
 
 
 
 
One IM injection in the deltoid 
muscle 
Refer to Section 3.5.2.2 

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Visit Number 
 
1 
2 
3 
4 
5 
Notes 
Type of Visit 
C 
C 
SC 
C 
SC 
SC/C 
 
Month Timepoint 
 
 
 
M1 
M3 
M6 
 
Visit Day  
Screeninga 
D1 
(Baseline) 
D8 
D29 
D91 
D181/ 
EoS 
 
Window Allowance (Days) 
-28 
N/A 
+3 
-7 to +3 
±5 
±14 
 
eDiary activation for recording solicited 
ARs/medication recording (7 days)d 
 
X 
 
 
 
 
Refer to Section 3.8.3.5 
Follow up safety calle 
 
 
X 
 
X 
Xi 
Refer to Section 3.8.3.4 
Review of solicited ARs eDiary 
 
X 
X 
 
 
 
 
Recording of unsolicited AEs 
 
X 
X 
X 
 
 
Refer to Section 3.8.3.7 and 
Section 5.3 
Recording of SAEs, AESIs, MAAEs, 
AEs leading to discontinuation from 
study participation, and concomitant 
medications/procedures relevant to or for 
their treatmentf 
 
X 
X 
X 
X 
X 
 
Recording of concomitant medicationsg 
 
X 
X 
X 
 
 
Refer to Section 3.6.6.2 
Recording of nonstudy vaccinationsh 
 
X 
X 
X 
X 
X 
Refer to Section 3.6.6.2 
Recording of concomitant 
procedures/surgeries 
 
X 
X 
X 
X 
X 
Refer to Section 3.6.6.2 
Study completion 
 
 
 
 
 
X 
 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; C = clinic/in-person visit; D = day; eDiary = electronic 
diary; EoS = end of study; IM = intramuscular(ly); M = month; MAAE = medically attended adverse event; SAE = serious adverse event; SC = safety call (or 
contact by electronic means). 

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a. 
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. 
b. 
Verbal medical history is acceptable. Clinically significant findings during the Screening Visit physical examination should also be recorded in the 
participant’s medical history. 
c. 
See Section 3.5.1, Table 9 for dose levels and treatment groups. 
d. 
The eDiary entries will be recorded at approximately 30 minutes after study intervention dosing while at the clinic with instruction provided by the clinic 
staff. Study participants will continue to record in the eDiary for solicited ARs each day after they leave the clinic, on the day of study intervention dosing 
and the subsequent 6 days following study intervention dosing. 
e. 
An unscheduled follow-up safety call may be triggered by the identification of a relevant safety event from an eDiary record, or other participant contact. A 
safety phone call may trigger an unscheduled visit. 
f. 
Trained clinic staff will call (or contact by electronic means) all participants to collect information relating to any MAAEs, AEs leading to discontinuation 
from study participation, SAEs, AESIs, information on concomitant medications associated with those events, and any nonstudy vaccinations. 
g. 
All concomitant medications will be recorded from Day 1 through Day 29; thereafter, only concomitant medications relevant to or for the treatment of an 
SAE, AESI, or MAAE will be recorded through Day 181 (Month 6)/EoS. 
h. 
All nonstudy vaccinations will be recorded through 181 days after the dose of study intervention. 
i. 
Samples for humoral immunogenicity on Day 181 (Month 6)/EoS will be collected for first 1000 participants and analyzed in a subset. Participants in the 
subset require a clinic visit on Day 181 (Month 6)/EoS for sample collection. All other participants will require a safety call. 

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3.2. 
Objectives and Endpoints (Part B)  
The objectives which will be evaluated in this study and endpoints associated with each objective 
are provided in Table 8. 
Table 8: 
Objectives and Endpoints (Part B)  
Objectives 
Endpoints 
Primary 
• 
To evaluate the humoral immunogenicity (for 
noninferiority) of mRNA-1010 relative to that 
of a licensed SD seasonal influenza vaccine 
(Fluarix Quadrivalent) against 4 vaccine-
matched influenza virus A and B strains at 
Day 29 in adults 18 to <65 years old. 
• 
GMT at Day 29 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 29 as measured by 
HAI. 
• 
To evaluate the safety, including 
reactogenicity, of mRNA-1010. 
• 
Frequency and severity of solicited local and 
systemic ARs during a 7-day follow-up 
period postinjection. 
• 
Frequency and severity of any unsolicited 
AEs during the 28-day follow-up period 
postinjection. 
• 
Frequency of any SAEs, MAAEs, AESIs, and 
AEs leading to discontinuation from Day 1 to 
Day 181/EoS. 
Secondary 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 (for superiority) relative to a 
licensed SD seasonal influenza vaccine 
(Fluarix Quadrivalent) against vaccine-
matched influenza A and B strains at Day 29. 
• 
GMT at Day 29 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 29 as measured by 
HAI. 
• 
To further evaluate the humoral 
immunogenicity of each study arm against 
vaccine-matched influenza A and B strains at 
Day 29. 
• 
The proportion of participants with HAI titer 
≥1:40 at Day 29. 
• 
GMFR comparing Day 29 to Day 1 
(Baseline) as measured by HAI. 
Exploratory (May be Performed) 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed SD 
seasonal influenza vaccine (Fluarix 
Quadrivalent) against vaccine-matched 
influenza virus A and B strains at 
Day 181/EoS in a subset of participants. 
• 
GMT at Day 181 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 181 as measured by 
HAI. 

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Objectives 
Endpoints 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed SD 
seasonal influenza vaccine (Fluarix 
Quadrivalent) against vaccine-matched or 
vaccine-mismatched A and B strains. 
• 
GMT and GMFR of nAbs by assays such as 
MN assays or alternative methods against 
vaccine-matched/mismatched strains on 
Day 29 compared with Day 1 (Baseline). 
• 
GMT and GMFR of anti-HA antibodies as 
measured by HAI against vaccine-
mismatched strains on Day 29 compared with 
Day 1 (Baseline). 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; EoS = end of 
study; GMFR = geometric mean fold rise; GMT = geometric mean titer; HA = hemagglutinin; 
HAI = hemagglutination inhibition; MAAE = medically attended adverse event; MN = microneutralization; 
mRNA = messenger ribonucleic acid; nAb = neutralizing antibody; SAE = serious adverse event; SD = standard 
dose. 
3.3. 
Study Design (Part B)  
3.3.1. 
Overall Design (Part B)  
mRNA-1010-P303 Part B is a Phase 3, randomized, stratified, observer-blind, active-controlled 
study to evaluate the immunogenicity, reactogenicity, and safety of mRNA-1010 seasonal 
influenza vaccine in adults 18 to <65 years old. 
mRNA-1010 to be tested contains 4 mRNAs in an equivalent mRNA mass ratio that encode 
membrane-bound HA of the 4 different influenza strains recommended by the WHO for 
2023-2024 NH cell- or recombinant-based vaccines. The licensed SD seasonal influenza vaccine, 
Fluarix Quadrivalent contains 4 HAs of the 4 different influenza strains recommended by the 
WHO for 2023-2024 NH egg-based vaccines. 
Medically stable adults (see Part B Exclusion Criterion # 3), aged 18 to <65 years, will be 
screened and enrolled. A complete list of inclusion and exclusion criteria is provided in 
Section 3.4. 
Approximately 3000 participants will be randomly assigned (see Section 3.6) to treatment in this 
study in a 1:1: ratio to 1 of 2 treatment groups to receive either a single dose of mRNA-1010 or a 
single dose of a licensed SD seasonal influenza vaccine (Fluarix Quadrivalent, Table 9). 
Table 9: 
Treatment Groups and Dose Levels (Part B)  
Treatment 
Group 
Study Intervention 
Received 
mRNA/Antigen 
Total Dose 
(µg) 
Number of 
Participants 
HA (each) (µg) 
3 
mRNA-1010  
12.5 (of mRNA) 
50 (of mRNA) 
1500 
4 
Active Comparator 
(Fluarix Quadrivalent) 
15 (of protein) 
60 (of protein) 
1500 
Abbreviations: HA = hemagglutinin; mRNA = messenger ribonucleic acid 
Table 7 displays the study SoA. Clinic/in-person visits will consist of a Screening Visit (up to 
28 days before the Day 1 Visit and may be performed over multiple visits if within the 28-day 
screening window), a dosing visit on Day 1 (Baseline; may be on the same day as the Screening 

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Visit), a visit on Day 29 (Month 1), and a subsequent visit on Day 181 (Month 6)/EoS [in a 
subset of ~ 1000 participants]), with up to 7 months of study participation for each participant. 
There will also be contacts by electronic means or telephone calls on Day 8, Day 91 (Month 3), 
and Day 181 (Month 6 [non-subset participants]). 
Table 7 displays the time periods for collecting solicited ARs via eDiary (Section 3.8.3.5) and 
unsolicited AEs. MAAEs, SAEs, AESIs and AEs leading to discontinuation will be collected 
from Day 1 to Day 181 (Month 6)/EoS. All participants will provide blood samples that may be 
used for assessment of GMT, GMFR, and seroconversion, as measured by HAI (Table 7 and 
Section 3.8.8). 
There may be situations in which the Investigator asks a participant to report for an unscheduled 
visit following the report of an AE. The eCRF should be completed for each unscheduled visit.  
This is an observer-blind study (refer to Section 3.6.1 for details). The Investigator may unblind 
in the event of an emergency (refer to Section 3.5.2.7 for details). 
An IST and CEAC will be involved (refer to Section 5.1.6 for details). 
3.3.2. 
Scientific Rationale for Study Design  
Part B of this study aims to demonstrate noninferiority of mRNA-1010 versus a licensed SD 
seasonal influenza vaccine (Fluarix Quadrivalent) in the immune response for all 4 strains, as 
measured by GMT and by seroconversion rate, in adults between the ages of 18 to <65 years. 
The rationale for using HAI as a surrogate endpoint of prevention of influenza illness and its 
complications is based on the established precedent of using HA-based immunologic correlates 
for clinical assessment and licensure of influenza vaccines (DHHS 2007a, DHHS 2007b, 
Dunning et al 2016, European Medicines Agency 2016). 
3.3.3. 
Justification for Dose  
The Sponsor has completed a Phase 1/2 study of mRNA-1010 (mRNA-1010-P101, 
NCT04956575) at dose levels up to 200 µg and is now conducting three Phase 3 studies at a 
50 µg dose level: mRNA-1010-P301, a safety and immunogenicity study (NCT05415462), 
mRNA-1010-P302, a safety and efficacy study (NCT05566639), and mRNA-1010-P303 Part A 
(NCT05827978). No safety concerns were identified with dose levels up to 200 µg. The 50-µg 
dose was chosen for the Phase 3 studies based on the observed reactogenicity and 
immunogenicity profile (refer to Section 1.2 for details). 
3.3.4. 
End of Study Definition  
See Section 2.3.4 for details. 
3.4. 
Study Population (Part B)  
Prospective approval of protocol deviations to recruitment and enrollment criteria, also known as 
protocol waivers or exemptions, is not permitted. 
3.4.1. 
Inclusion Criteria (Part B)  
Participants are eligible to be included in the study only if all of the following criteria are met: 

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Age 
1. At least 18 and <65 years of age, at the time of signing the ICF. 
Type of Participant and Disease Characteristics 
2. Investigator has assessed that the participant understands and is willing and 
physically able to comply with protocol mandated follow-up, including all 
procedures. 
Sex and Contraceptive/Barrier Requirements 
3. Participants AFAB are eligible to participate if they are not pregnant or 
breastfeeding/chestfeeding/bodyfeeding, and one of the following conditions applies: 
• Is a PONCBP as defined in Section 5.6. 
• Is a POCBP and using an acceptable contraceptive method as described in Section 5.6 
from at least 28 days before the dose of study intervention and during the study 
intervention period (at a minimum until 90 days after the dose of study intervention). 
• A POCBP must have a negative highly sensitive pregnancy test (urine or serum as 
required by local regulations) at the Screening Visit and before the dose of study 
intervention, if Day 1 is not on the same day as the Screening Visit (see 
Section 3.8.3.3). 
− If a urine test cannot be confirmed as negative (eg, an ambiguous result), a serum 
pregnancy test is required. In such cases, the participant must be excluded from 
participation if the serum pregnancy result is positive. 
• Additional requirements for pregnancy testing during and after study intervention are 
located in Section 3.8.3.3. 
• The Investigator is responsible for review of medical history, menstrual history, and 
recent sexual activity to decrease the risk for inclusion of a person with an early 
undetected pregnancy. 
Informed Consent 
4. Capable of giving signed informed consent as described in Section 5.1.3 which includes 
compliance with the requirements and restrictions listed in the ICF and in this protocol. 
3.4.2. 
Exclusion Criteria (Part B)  
Participants are excluded from the study if any of the following criteria apply: 
Medical Conditions 
1. Acutely ill or febrile (temperature ≥38.0℃ [100.4°F]) within 72 hours prior to Day 1. 
Participants meeting this criterion may be rescheduled within the 28-day screening 
window.  
2. Close contact with someone with laboratory-confirmed influenza infection or with 
someone who has been treated with antiviral therapies for influenza (eg, Tamiflu) within 
the past 5 days prior to Day 1. 

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3. History of a diagnosis or condition that, in the judgment of the Investigator, is clinically 
unstable or may affect participant safety, assessment of safety endpoints, assessment of 
immune response, or adherence to study procedures. Clinically unstable is defined as a 
diagnosis or condition requiring significant changes in management or medication within 
the 60 days prior to Day 1 and includes ongoing workup of an undiagnosed illness that 
could lead to a new diagnosis or condition. 
• Asymptomatic conditions and conditions with no clinically significant end organ 
involvement (eg, mild hypertension, dyslipidemia) are not exclusionary, if they are 
being appropriately managed and are clinically stable (ie, unlikely to result in 
symptomatic illness within the time course of this study). Illnesses or conditions may 
be exclusionary, even if otherwise stable, due to therapies used to treat them (eg, 
immune-modifying treatments), at the discretion of the Investigator. 
• Participants who have undergone surgical procedures within 7 days prior to Day 1 or 
are scheduled to undergo a surgical procedure within 28 days after study intervention 
dosing are also excluded. However, minor surgical procedures under local anesthesia 
(eg, excision of skin lesion) or diagnostic procedures (eg, colonoscopy) are allowed. 
4. Reported history of congenital or acquired immunodeficiency, immunosuppressive 
condition or immune-mediated disease, asplenia, or recurrent severe infections. The 
following conditions are permitted at the discretion of the Investigator: 
• Participants who are HIV positive and on antiviral therapy with cluster of 
differentiation 4 count ≥350 cells/mm3 and HIV RNA ≤500 copies/mL within the past 
12 months. 
• Participants with immune-mediated diseases which are stable (eg, Hashimoto’s 
thyroiditis and type 1 diabetes) or conditions such as asthma, psoriasis, vitiligo, gout, 
alopecia areata, or auto-immune ovarian failure, which do not require systemic 
immunosuppressants per Part B Exclusion Criterion # 13. 
5. Dermatologic conditions that could affect local solicited AR assessments (eg, tattoos; 
psoriasis patches affecting skin over the deltoid areas). 
6. Participant has tested positive for influenza by local health authority-approved testing 
methods within 180 days prior to Day 1. 
7. Reported history of anaphylaxis or severe hypersensitivity reaction after receipt of 
mRNA vaccines or any components of the mRNA-1010 or influenza vaccines, including 
egg protein. 
8. Reported history of coagulopathy or bleeding disorder that is considered a 
contraindication to IM injection or phlebotomy. 
9. Malignancy within the previous 2 years (excluding nonmelanoma skin cancer). 
10. History of myocarditis, pericarditis, or myopericarditis within 180 days prior to Day 1 or 
have not returned to Baseline clinical status. Participants who have not returned to 
Baseline after their convalescent period will also be excluded. 
11. History of Guillain-Barre syndrome after any influenza vaccine. 

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12. Any medical, psychiatric, or occupational condition, including reported history of drug or 
alcohol abuse, that, in the opinion of the Investigator, might pose additional risk due to 
participation in the study or could interfere with the interpretation of study results. 
Prior/Concomitant Therapy 
13. Participant has received systemic immunosuppressants or immune-modifying drugs that 
may impact the immune response for >14 days in total within 180 days prior to Day 1 
(for corticosteroids, ≥10 mg/day of prednisone or equivalent) or is anticipating the need 
for systemic immunosuppressive treatment at any time during participation in the study. 
Inhaled, nasal, and topical steroids are allowed. Intra-articular and epidural steroid 
injections are not allowed within 28 days before and/or after study intervention dosing. 
14. Participant has received any vaccine authorized or approved by local health agency 
≤28 days prior to study intervention dosing (Day 1) or plans to receive a vaccine 
authorized or approved by local health agency within 28 days before or after study 
intervention dosing. 
15. Participant has received a licensed seasonal influenza vaccine within 6 months (180 days) 
prior to Day 1. 
16. Participant has participated in any investigational seasonal influenza vaccine study where 
the study vaccine was administered within 12 months prior to Day 1. Participants who 
were previously enrolled in mRNA-1010-P303 Part A are not eligible to participate in 
Part B. 
17. Participant is not aware whether they have received an influenza vaccine since September 
2022. 
18. Participant has been treated with antiviral therapies for influenza (eg, Tamiflu) within 
180 days prior to Day 1. 
19. Participant has received systemic immunoglobulins or blood products within 90 days 
prior to Day 1 or plans to receive systemic immunoglobulins or blood products during the 
study. In addition, participants who have received long-acting biological therapies that 
affect immune responses (eg, infliximab) within 90 days prior to Day 1, or plan to receive 
them, are also excluded. 
20. Participant has donated ≥450 mL of blood products within 28 days prior to Day 1 or 
plans to donate blood products during the study. 
Other Exclusion Criteria 
21. Participant has participated in an interventional clinical study within 28 days prior to 
Day 1, based on the medical history interview or plans to do so while participating in this 
study. Participants may continue in prior interventional study follow-up activities, as long 
as it does not involve further investigational treatment other than the study intervention 
described in this protocol (Note: interventions such as counseling, biofeedback, and 
cognitive therapy are not exclusionary). 
22. Participant is working or has worked as study personnel or is an immediate family 
member or household member of study personnel, study site staff, or Sponsor personnel. 

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3.4.3. 
Screen Failures  
See Section 2.4.3 for details. 
3.4.4. 
Criteria for Temporarily Delaying the Day 1 Visit  
See Section 2.4.4 and Section 3.7 for details, and refer to SoA for Part B (Table 7). 
3.5. 
Study Intervention(s) and Concomitant Therapy (Part B)  
Study intervention(s) refers to the mRNA-1010 vaccine and to the licensed SD seasonal 
influenza vaccine (Fluarix Quadrivalent) intended to be administered to the study participants 
during the study conduct. 
3.5.1. 
Study Intervention(s) Administered  
The study intervention(s) to be administered and the treatment groups in the study are provided 
in Table 10. 
The mRNA-1010 vaccine will be administered as a single 0.5 mL IM injection at an mRNA total 
dose level of 50 µg to participants according to the treatment group assignment. 
The active comparator administered in this study is a licensed SD seasonal influenza vaccine, 
Fluarix Quadrivalent administered as a single 0.5 mL IM injection. 
Table 10: 
Study Intervention(s) Administered  
Intervention Label 
mRNA-1010.4 
Fluarix 
Treatment Group 
Type 
Experimental 
Active comparator 
Intervention Name 
mRNA-1010  
Fluarix SD Quadrivalent 
Intervention 
Description 
mRNA-1010 contains LNP dispersion 
encoding the seasonal influenza 
vaccine antigens, HAs, from the 
strains recommended by the WHO for 
2023 to 2024 NH cell or recombinant-
based vaccines. 
All mRNAs are formulated in LNPs 
composed of 4 lipids and provided as 
a sterile liquid for injection, white-to-
off white dispersion in appearance, at 
a concentration of 0.10 mg/mL in 
20 mM Tris buffer with 87 g/L 
sucrose, and 2.2 mM sodium acetate 
at pH 7.5. 
Licensed quadrivalent seasonal 
vaccine 
Fluarix Quadrivalent contains the 
seasonal influenza vaccine antigens, 
HAs, from the strains recommended 
by the WHO for 2023 to 2024 NH 
egg-based vaccines. 
Type 
Vaccine 
Vaccine 
Dosage Level(s) 
50 µg of mRNA 
Single dose 
60 µg of proteins 
Single dose  

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Intervention Label 
mRNA-1010.4 
Fluarix 
Route of 
Administration 
IM 
IM 
Use 
Experimental 
Active control 
IMP and AxMP 
IMP 
IMP 
Sourcing 
By Sponsor 
By Sponsor 
Packaging and 
Labeling 
The study intervention will be 
prepared, packaged, and labeled in 
accordance with the standard 
operating procedures of ModernaTX, 
Inc. or those of its designee, CFR 
Title 21, GMP guidelines, ICH and 
GCP guidelines, guidelines for 
Quality System Regulations, and 
applicable regulations. 
The study intervention will be 
prepared, packaged, and labeled in 
accordance with the standard 
operating procedures of ModernaTX, 
Inc. or those of its designee, CFR 
Title 21, GMP guidelines, ICH and 
GCP guidelines, guidelines for 
Quality System Regulations, and 
applicable regulations. 
Abbreviations: AxMP = auxiliary medicinal product; CFR = Code of Federal Regulations; GCP = Good Clinical 
Practice; GMP = Good Manufacturing Practice; HA = hemagglutinin; ICH = International Council for 
Harmonisation of Technical Requirements for Pharmaceuticals for Human Use; IM = intramuscular(ly); 
IMP = investigational medicinal product; LNP = lipid nanoparticle; mRNA = messenger ribonucleic acid; 
NH = Northern Hemisphere; SD = standard dose; WHO = World health Organization. 
3.5.2. 
Preparation, Handling, Storage, and Accountability  
See Section 2.5.2 for details. 
3.5.2.1. 
Study Intervention(s) Preparation  
The study intervention will be prepared for each participant based on their treatment group 
assignment. The mRNA-1010 vaccine will be administered as a single 0.5 mL IM injection and 
will contain mRNA-1010 at a dose of 50 µg. The licensed SD seasonal influenza vaccine 
(Fluarix Quadrivalent) will be administered at a volume of 0.5 mL. The mRNA-1010 and the 
licensed SD seasonal influenza vaccine (Fluarix Quadrivalent) preparation instructions are 
detailed in the Pharmacy Manual. 
3.5.2.2. 
Study Intervention(s) Administration  
The study intervention (mRNA-1010) or the licensed SD seasonal influenza vaccine (Fluarix 
Quadrivalent) will be administered as a single IM injection into the deltoid muscle on Day 1. 
Preferably, the study intervention should be administered into the nondominant arm. 
Participants will be monitored for a minimum of 30 minutes after administration of the study 
intervention. Assessments will include vital sign measurements and monitoring for solicited ARs 
as shown in the SoA for Part B (Table 7) 
The clinic will be appropriately staffed with individuals with basic cardiopulmonary 
resuscitation training/certification. Either onsite resuscitation equipment and personnel or 
appropriate protocols for the rapid transport of a participant to a resuscitation area or facility are 
required. 

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Further instructions for the preparation and administration of mRNA-1010 and licensed SD 
seasonal influenza vaccine (Fluarix Quadrivalent) are described in the Pharmacy Manual. 
3.5.2.3. 
Study Intervention(s) Packaging and Labeling  
See Section 2.5.2.3 for details. 
3.5.2.4. 
Study Intervention(s) Storage  
mRNA-1010 must be stored at the clinical site at 2°C to 8°C in a secure area with limited access 
and must be protected from moisture and light until it is prepared for administration 
(Section 3.5.2.1). The refrigerator should have automated temperature recording and a 24-hour 
alert system in place that allows for rapid response in case of refrigerator malfunction. The 
refrigerator should be connected to a backup generator. In addition, for study intervention 
accountability, staff are required to keep a temperature log to establish a record of compliance 
with these storage conditions. The clinic is responsible for reporting any study intervention that 
was not temperature controlled during shipment or storage. Such study intervention will be 
retained for inspection by the monitor and disposed of according to approved methods. Please 
note that mRNA-1010 will be stored at -25°C to - 15°C at the depots and during shipments to the 
clinical sites. 
The licensed SD seasonal influenza vaccine (Fluarix Quadrivalent) should be stored in its 
original container and in accordance with the instructions in the Pharmacy Manual. 
3.5.2.5. 
Study Intervention(s) Accountability  
See Section 2.5.2.5 for details. 
3.5.2.6. 
Study Intervention(s) Handling and Disposal  
See Section 2.5.2.6 for details. 
3.5.2.7. 
Unblinding  
See Section 2.5.2.7 for details. 
3.6. 
Assignment to Study Intervention (Part B)  
Randomization will be performed using an IRT. Approximately 3000 participants will be 
randomly assigned to treatment in this study in a 1:1 ratio to 1 of 2 treatment groups to receive 
either a single dose of mRNA-1010 or a single dose of a licensed SD seasonal influenza vaccine 
(Fluarix Quadrivalent, Table 10). Randomization will be stratified by previous flu season (since 
September 2022) vaccination status (received or not received; if received, was it from prior 
participation in the mRNA-1010-P302 study [yes/no]). 
3.6.1. 
Blinding  
See Section 2.6.1 for details. 
3.6.2. 
Study Intervention Compliance  
See Section 2.6.2 for details. 

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3.6.3. 
Dose Modification  
Not applicable. 
3.6.4. 
Continued Access to Study Intervention After the End of the Study  
See Section 2.6.4 for details. 
3.6.5. 
Treatment of Overdose  
See Section 2.6.5 for details. 
3.6.6. 
Prior and Concomitant Therapy  
See Section 2.6.6 for details. 
3.6.6.1. 
Prohibited Therapy  
See Section 2.6.6.1 for details. 
3.6.6.2. 
Recording of Concomitant Medications, Concomitant Vaccinations and 
Concomitant Procedures  
See Section 2.6.6.2 for details. 
3.6.6.3. 
Concomitant Medications and Vaccines That May Lead to the Elimination of a 
Participant From Per-protocol Analyses  
See Section 2.6.6.3 for details. 
3.7. 
Discontinuation of Study Intervention and Participant 
Discontinuation/Withdrawal (Part B)  
Discontinuation of specific sites or of the study as a whole are detailed in Section 5.1.10. 
3.7.1. 
Discontinuation of Study Intervention  
Not applicable. 
3.7.2. 
Participant Discontinuation/Withdrawal from the Study  
See Section 2.7.1.1 for details and refer to SoA for Part B (Table 7). 
3.7.3. 
Lost to Follow-up  
See Section 2.7.1.2 for details. 
3.7.4. 
Pause Rules  
Not applicable. 
3.8. 
Study Assessments and Procedures (Part B)  
See Section 2.8 for details and refer to SoA for Part B (Table 7). 

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3.8.1. 
Demography  
See Section 2.8.1 for details. 
3.8.2. 
Immunogenicity Assessments  
Planned timepoints for all immunogenicity assessments are provided in the SoA for Part B 
(Table 7). 
The following analytes will be measured: 
• Serum antibody level as measured by HAI assay. 
• Serum neutralizing antibody level as measured by microneutralization assay or 
similar methods may also be performed. 
Measurement of antibody levels will be performed in a laboratory designated by the Sponsor. 
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 influenza vaccines, 
additional assay development, and the immune response across influenza viruses. 
3.8.3. 
Safety Assessments  
See Section 2.8.3 for details and refer to SoA for Part B (Table 7). 
3.8.3.1. 
Physical Examinations  
See Section 2.8.3.1 for details and refer to SoA for Part B (Table 7). 
3.8.3.2. 
Vital Signs  
See Section 2.8.3.2 for details and refer to SoA for Part B (Table 7). 
3.8.3.3. 
Pregnancy Testing  
See Section 2.8.3.3 for details and refer to SoA for Part B (Table 7). 
3.8.3.4. 
Safety Phone Calls  
See Section 2.8.3.5 for details and refer to SoA for Part B Table 7). 
3.8.3.5. 
Use of Electronic Diaries  
See Section 2.8.3.6 for details and refer to SoA for Part B (Table 7). 
3.8.3.6. 
Ancillary Supplies for Participant Use  
See Section 2.8.3.7 for details and refer to SoA for Part B Table 7. 
3.8.3.7. 
AEs, SAEs, and Other Safety Reporting  
The definitions of AEs, SAEs, solicited ARs, and unsolicited AEs can be found in Section 5.3. 
See Section 2.8.3.8 for details. 

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3.8.3.7.1. Time Period and Frequency for Collecting AE and SAE Information  
See Section 2.8.3.8.1 for details. 
3.8.3.7.2. Method of Detecting AEs and SAEs  
See Section 2.8.3.8.2 for details and refer to SoA for Part B Table 7). 
3.8.3.7.3. Follow-up of AEs and SAEs  
See Section 2.8.3.8.3 and refer to SoA for Part B (Table 7). 
3.8.3.7.4. Regulatory Reporting Requirements for SAEs  
See Section 2.8.3.8.4 for details. 
3.8.3.7.5. Pregnancy  
Refer to Section 2.8.3.8.5 for details and refer to SoA for Part B (Table 7). 
3.8.3.8. 
Solicited Adverse Reactions  
See Section 2.8.3.9 for details and refer to SoA for Part B (Table 7). 
3.8.3.9. 
Medically Attended Adverse Events  
The definition of MAAE is provided in Section 5.3.3. 
3.8.3.10. Adverse Events of Special Interest  
The definition of AESI is provided in Section 5.3.4. AESIs for this protocol are listed in 
Section 5.3. 
3.8.3.10.1. Anaphylaxis  
See Section 2.8.3.11.1 for details. 
3.8.3.10.2. Myocarditis and/or Pericarditis  
See Section 2.8.3.11.2 for details. 
3.8.4. 
Pharmacokinetics  
Pharmacokinetic parameters are not evaluated in this study. 
3.8.5. 
Pharmacodynamics  
Pharmacodynamic parameters are not evaluated in this study. 
3.8.6. 
Genetics  
N/A. 
3.8.7. 
Biomarkers  
N/A. 

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3.8.8. 
Immunogenicity Assessments  
See Section 2.8.8 for details and refer to SoA for Part B (Table 7). 
3.8.9. 
Health Economics or Medical Resource Utilization and Health Economics  
Health economics or medical resource utilization and health economics parameters are not 
evaluated in this study. 
3.9. 
Statistical Considerations (Part B)  
See Section 2.9 for details. 
3.9.1. 
Blinding and Responsibility for Analyses  
See Section 2.9.1 and Section 3.9.6 for details. 
3.9.2. 
Statistical Hypotheses  
The primary objective in Part B is to evaluate the noninferiority of the immunogenicity response 
to mRNA-1010 versus the licensed SD Fluarix Quadrivalent vaccine, as measured by GMT and 
seroconversion rate at Day 29 using HAI assay, for all 4 vaccine-matched influenza virus A and 
B strains:  
• For each of the 4 vaccine-matched strains, the noninferiority hypothesis in terms of 
the GMT is: 
Null hypothesis:  
H01:  GMR ≤0.667 (inferior) vs. 
Alternative hypothesis: 
Ha1:  GMR >0.667 (noninferior), 
using a noninferiority margin of 1.5, where the GMR is the ratio of the GM HAI titer 
in the mRNA-1010 group compared with the GM HAI titer in the Fluarix 
Quadrivalent group. 
• For each of the 4 vaccine-matched strains, the noninferiority hypothesis in 
seroconversion rate is: 
Null hypothesis:  
H02: SCR difference ≤-10% (inferior) vs. 
Alternative hypothesis: 
Ha2:  SCR difference >-10% (noninferior) 
using a noninferiority margin of 10%, where the SCR difference is the difference in 
the SCR between the mRNA-1010 group compared with the Fluarix Quadrivalent 
group. 
The noninferiority hypotheses in the GMT and SCR will be evaluated for all 4 strains, and Part B 
is considered a study success if all the 8 coprimary immunogenicity endpoints meet the 
noninferiority criteria. Therefore, each of the coprimary immunogenicity endpoints will be tested 
at 1-sided alpha of 0.025 level.  
• For each strain, the noninferiority in GMT will be demonstrated by the lower bound 
of the 95% CI of the GMR ruling out 0.667, ie, the lower bound of the 95% CI 
>0.667. 

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• For each strain, the noninferiority in SCR will be demonstrated by the lower bound of 
the 95% CI of the SCR difference ruling out −10%, ie, the lower bound of the 95% 
CI >-10%. 
Upon successful demonstration of noninferiority for Part B, ie, the noninferiority success criteria 
have been met for all 8 coprimary immunogenicity endpoints, the following superiority 
hypotheses will be tested: 
• For each of the 4 vaccine-matched strains, the superiority hypothesis in terms of the 
GMT is: 
Null hypothesis:  
H03: GMR = 1 vs. 
Alternative hypothesis: 
Ha3: GMR >1 (superior) 
• For each of the 4 vaccine-matched strains, the superiority hypothesis in 
seroconversion rate is: 
Null hypothesis:  
H04: SCR difference = 0 vs. 
Alternative hypothesis: 
Ha4: SCR difference >0 (superior) 
The multiplicity adjustment procedures for the superiority tests of the 8 immunogenicity 
endpoints are specified in Section 4.9.7 (also see Figure 1). 
3.9.3. 
Sample Size Determination  
Assuming approximately 15% of 3000 randomized participants will be excluded from the PP 
Immunogenicity Set, with approximately 2550 participants in the PP Immunogenicity Set 
(1:1 ratio; approximately 1275 participants in each group): 
• The study has at least 99% power to meet the noninferiority success criteria in 
GMT for all 4 strains at a 1-sided alpha of 0.025 level with a noninferiority margin 
of 1.5. An underlying GMR (mRNA-1010 vs. the licensed SD Fluarix Quadrivalent 
vaccine) of 0.95 is assumed for each of the 4 strains and the standard deviation of 
the natural log-transformed levels is assumed to be 1.5. 
• The study has at least 98% power to meet the noninferiority success criteria in SCR 
for all 4 strains, at a 1-sided alpha of 0.025 level with a noninferiority margin of 
10%. The SCRs of 58% for influenza A strains and 48% for influenza B strains are 
assumed in the mRNA-1010 group, whereas the SCRs for influenza A and B strains 
in the licensed SD Fluarix Quadrivalent group are assumed to be 59% and 49%, 
respectively. 
The overall power for achieving the primary noninferiority objective in Part B is approximately 
98%. Furthermore, the sample size provides 1) an approximately 79.5% power for a superiority 
test of GMT for an individual strain with an underlying GMR of 1.2 (mRNA-1010 vs. Fluarix 
SD Quadrivalent); 2) an approximately 63% power for a superiority test of SCR for an A strain 
(assuming a 64% SCR for mRNA-1010 and 59% for Fluarix SD Quadrivalent) and an 
approximately 61% power for a B strain (assuming a 54% SCR for mRNA-1010 vs. 49% for 
Fluarix SD Quadrivalent) at 2-sided alpha of 0.025 (with alpha split for multiplicity adjustment). 

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3.9.4. 
Analysis Sets  
See Section 2.9.4 for details. 
3.9.5. 
Statistical Analyses  
See Section 2.9.5 for details. 
3.9.5.1. 
Immunogenicity Analyses  
The immunogenicity analyses for Part B will be conducted separately. See Section 2.9.5.1 for 
details. 
3.9.5.2. 
Adverse Events  
See Section 2.9.5.2 for details. 
3.9.5.3. 
Exploratory Analyses  
Exploratory analyses will be described in the SAP before database lock. 
3.9.6. 
Planned Analyses  
3.9.6.1. 
Primary Analyses  
The primary analysis of safety and immunogenicity for Part B will be performed after all participants 
have completed the Day 29 visit. All data relevant to the primary study analysis through the Day 29 
visit will be cleaned for the primary analysis (ie, data that are as clean as possible) and a report may be 
generated. 
The analysis will be performed by a separate team of unblinded programmers and statisticians. 
More details can be found in the study data blinding plan. 
3.9.6.2. 
Final Analysis  
Final analysis of all safety and immunogenicity data in Part B will be performed once all 
participants complete the Day 181 (Month 6)/EoS Visit. 
3.9.7. 
Multiplicity  
No multiplicity adjustment will be applied for the primary noninferiority objective because 
Part B is successful only if all the 8 coprimary immunogenicity endpoints meet the noninferiority 
criteria. Each of the coprimary immunogenicity endpoints will be tested at 1-sided alpha of 0.025 
level. 
Upon successful demonstration of the noninferiority, the superiority hypotheses specified in 
Section 3.9.2 will be tested following the prespecified order as illustrated in Figure 1. 

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Figure 1: 
Prespecified Order for Superiority Hypothesis Testing  
 
Abbreviations: GMT = geometric mean titer; GMR = geometric mean ratio; LB = lower bound. 
a. 
If both hypotheses at the previous step are successful, the hypothesis at the current step will be tested at two-
sided alpha of 0.025; if only one hypothesis at the previous step is successful, the current hypothesis will be 
tested at two-sided alpha of 0.0125. 
b. 
The hypothesis will be tested at the same alpha level from the previous step (if success achieved at previous 
steps). 

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4. 
PART C  
4.1. 
Protocol Summary  
4.1.1. 
Synopsis (Part C)  
Rationale:  
The Sponsor is conducting this Part C of its Phase 3 study, mRNA-1010-P303, to further 
evaluate its candidate seasonal influenza mRNA vaccine (mRNA-1010) to establish 
immunogenicity and safety in support of licensure. Part C will evaluate the immune response of 
mRNA-1010 compared to a high dose seasonal influenza vaccine (Fluzone® HD) in adults ≥65 
years old. Because of increased morbidity and mortality associated with influenza infections in 
older adults, Fluzone HD Quadrivalent vaccine is one of 3 influenza vaccines (along with 
Flublok® Quadrivalent and Fluad® Quadrivalent) that is preferentially recommended for people 
65 years and older. This preferential recommendation was new for the 2022 to 2023 season. 
Interim analysis results from a Phase 1/2 study suggested immune responses of mRNA-1010 
were on par with immune responses to Fluzone HD. The design of this study will include 
immunogenicity objectives for HAI, a surrogate endpoint of prevention of influenza illness and 
its complications. The rationale for this approach is based on the established precedent of using 
HA-based immunologic correlates for clinical assessment and licensure of influenza vaccines 
(DHHS 2007 a, DHHS 2007b, Dunning et al 2016, European Medicines Agency 2016).  
Objectives and Endpoints 
Objectives 
Endpoints 
Primary 
• 
To evaluate the humoral immunogenicity (for 
noninferiority) of mRNA-1010 relative to that 
of a licensed HD seasonal influenza vaccine 
(Fluzone HD) against 4 vaccine-matched 
influenza virus A and B strains at Day 29 in 
adults ≥65 years old. 
• 
GMT at Day 29 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 29 as measured by 
HAI. 
• 
To evaluate the reactogenicity and safety of 
mRNA-1010. 
• 
Frequency and severity of solicited local and 
systemic reactogenicity ARs during a 7-day 
follow-up period postinjection. 
• 
Frequency and severity of any unsolicited 
AEs during the 28-day follow-up period 
postinjection. 
• 
Frequency of any SAEs, MAAEs, AESIs, and 
AEs leading to discontinuation from Day 1 to 
Day 181/EoS. 

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Objectives 
Endpoints 
Secondary 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 (for superiority) relative to a 
licensed HD seasonal influenza vaccine 
(Fluzone HD) against vaccine-matched 
influenza A and B strains at Day 29. 
• 
GMT at Day 29 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 29 as measured by 
HAI. 
• 
To further evaluate the humoral 
immunogenicity of each study arm against 
vaccine-matched influenza A and B strains at 
Day 29. 
• 
The proportion of participants with HAI titer 
≥1:40 at Day 29. 
• 
GMFR comparing Day 29 to Day 1 
(Baseline) as measured by HAI 
Exploratory (May be Performed) 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed HD 
seasonal influenza vaccine (Fluzone HD) 
against vaccine-matched influenza virus A and 
B strains at Day 181/EoS in a subset of 
participants. 
• 
GMT at Day 181 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 181 as measured by 
HAI. 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed HD 
seasonal influenza vaccine (Fluzone HD) 
against vaccine-matched or vaccine-
mismatched A and B strains. 
• 
GMT and GMFR of nAbs by assays such as 
MN assays or alternative methods against 
vaccine-matched/mismatched strains on Day 
29 compared with Day 1 (Baseline). 
• 
GMT and GMFR of anti-HA antibodies as 
measured by HAI against vaccine-
mismatched strains on Day 29 compared with 
Day 1 (Baseline). 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction EoS = end of 
study; GMFR = geometric mean fold rise; GMT = geometric mean titer; HA = hemagglutinin; 
HAI = hemagglutination inhibition; HD = high dose; MAAE = medically attended adverse event; 
MN = microneutralization; mRNA = messenger ribonucleic acid; nAb = neutralizing antibody. 
Overall Design Synopsis: 
mRNA-1010-P303 Part C is a Phase 3, randomized, stratified, observer-blind, active-controlled 
study to evaluate the immunogenicity, reactogenicity, and safety of mRNA-1010 seasonal 
influenza vaccine in adults ≥65 years old. 
Approximately 3000 medically stable adults ≥65 years of age, at the time of signing the ICF, will 
be randomly assigned to treatment in this study in a 1:1: ratio to 1 of 2 treatment groups to 
receive either a single dose of mRNA-1010 or a single dose of a licensed HD seasonal influenza 
vaccine (Fluzone HD) at Day 1. Randomization will be stratified by the previous flu season 
(since September 2022) vaccination status (received or not received; if received, was it from 
prior participation in the mRNA-1010-P302 study [yes/no]). 

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Brief Summary: 
The study aims to demonstrate noninferiority of mRNA-1010 versus the licensed HD seasonal 
influenza vaccine (Fluzone HD) in the immune response, as measured by GMT and by 
seroconversion rate at Day 29, using HAI assay, for each of the 4 vaccine-matched influenza 
virus A and B strains. 
Study details include: 
• There will be 3 or 4 clinic/in-person visits (Screening Visit and at Days 1, 29, and 
Day 181 [Month 6]/EoS [in a subset of ~ 1000 participants]) and 2 to 3 safety phone 
call at Days 8, 91, and 181 (non-subset participants) as specified in the SoA. The 
Screening Visit and Day 1 may be performed on the same day or a different day. 
• All participants will be asked to complete an eDiary for solicited ARs for 7 days (ie, 
the day of study intervention dosing and 6 subsequent days). 
• Detection of all AEs will be through 28 days after study intervention dosing (ie, the 
day of study intervention dosing and 27 subsequent days). Detecting MAAEs, AESI, 
SAEs, and AEs leading to discontinuation from study participation will continue 
through Day 181 (Month 6)/EoS. 
Number of Participants: Approximately 3000 participants will be enrolled. 
Study Arms and Duration: 
• Part C will comprise 2 study arms: investigational vaccine (mRNA-1010) group and 
licensed HD seasonal influenza vaccine (Fluzone HD) group. 
• The total study duration (including screening) for each participant is up to 7 months. 

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4.1.2. 
SoA (Part C)  
Table 11: 
Schedule of Activities (Part C)  
Visit Number 
 
1 
2 
3 
4 
5 
Notes 
Type of Visit 
C 
C 
SC 
C 
SC 
SC/C 
 
Month Timepoint 
 
 
 
M1 
M3 
M6 
 
Visit Day  
Screeninga 
D1 
(Baseline) 
D8 
D29 
D91 
D181/ 
EoS 
 
Window Allowance (Days) 
-28 
N/A 
+3 
-7 to +3 
±5 
±14 
 
Informed consent form, demographics, 
concomitant medications, medical 
historyb 
X 
 
 
 
 
 
 
Inclusion/exclusion criteria 
X 
X 
 
 
 
 
Refer to Section 4.4.1 and 
Section 4.4.2 
Physical examinationb 
X 
 
 
 
 
 
Refer to Section 4.8.3.1 
Vital signs measurements 
X 
X 
 
 
 
 
Refer to Section 4.8.3.2 
Randomization 
 
X 
 
 
 
 
Refer to Section 4.6 
Blood collection for humoral 
immunogenicity 
 
X 
 
X 
 
Xi 
Prior to study intervention dosing 
on Day 1 
Study intervention dosing (including 30-
minute, postdose observation period)c 
 
X 
 
 
 
 
One IM injection in the deltoid 
muscle 
Refer to Section 4.5.2.2 
eDiary activation for recording solicited 
ARs/medication recording (7 days)d 
 
X 
 
 
 
 
Refer to Section 4.8.3.6 
Follow up safety calle 
 
 
X 
 
X 
Xi 
Refer to Section 4.8.3.3 

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Visit Number 
 
1 
2 
3 
4 
5 
Notes 
Type of Visit 
C 
C 
SC 
C 
SC 
SC/C 
 
Month Timepoint 
 
 
 
M1 
M3 
M6 
 
Visit Day  
Screeninga 
D1 
(Baseline) 
D8 
D29 
D91 
D181/ 
EoS 
 
Window Allowance (Days) 
-28 
N/A 
+3 
-7 to +3 
±5 
±14 
 
Review of solicited ARs eDiary 
 
X 
X 
 
 
 
 
Recording of unsolicited AEs 
 
X 
X 
X 
 
 
Refer to Section 4.8.3.6 and 
Section 5.3 
Recording of SAEs, AESIs, MAAEs, 
AEs leading to discontinuation from 
study participation, and concomitant 
medications/procedures relevant to or for 
their treatmentf 
 
X 
X 
X 
X 
X 
 
Recording of concomitant medicationsg 
 
X 
X 
X 
 
 
Refer to Section 4.6.6.2 
Recording of nonstudy vaccinationsh 
 
X 
X 
X 
X 
X 
Refer to Section 4.6.6.2 
Recording of concomitant 
procedures/surgeries 
 
X 
X 
X 
X 
X 
Refer to Section 4.6.6.2 
Study completion 
 
 
 
 
 
X 
 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; C = clinic/in-person visit; D = day; eDiary = electronic 
diary; EoS = end of study; IM = intramuscular(ly); M = month; MAAE = medically attended adverse event; SAE = serious adverse event; SC = safety call (or 
contact by electronic means). 
a. 
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. 
b. 
Verbal medical history is acceptable. Clinically significant findings during the Screening Visit physical examination should also be recorded in the 
participant’s medical history. 
c. 
See Section 4.5.1, Table 13 for dose levels and treatment groups. 

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d. 
The eDiary entries will be recorded at approximately 30 minutes after study intervention dosing while at the clinic with instruction provided by the clinic 
staff. Study participants will continue to record in the eDiary for solicited ARs each day after they leave the clinic, on the day of study intervention dosing 
and the subsequent 6 days following study intervention dosing. 
e. 
An unscheduled follow-up safety call may be triggered by the identification of a relevant safety event from an eDiary record, or other participant contact. A 
safety phone call may trigger an unscheduled visit. 
f. 
Trained clinic staff will call (or contact by electronic means) all participants to collect information relating to any MAAEs, AEs leading to discontinuation 
from study participation, SAEs, AESIs, information on concomitant medications associated with those events, and any nonstudy vaccinations. 
g. 
All concomitant medications will be recorded from Day 1 through Day 29; thereafter, only concomitant medications relevant to or for the treatment of an 
SAE, AESI, or MAAE will be recorded through Day 181 (Month 6)/EoS. 
h. 
All nonstudy vaccinations will be recorded through 181 days after the dose of study intervention. 
i. 
Samples for humoral immunogenicity on Day 181 (Month 6)/EoS will be collected for approximately the first 1000 participants and analyzed in a subset. 
Participants in the subset require a clinic visit on Day 181 (Month 6)/EoS for sample collection. All other participants will require a safety call. 

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4.2. 
Objectives and Endpoints (Part C)  
The objectives which will be evaluated in this study and endpoints associated with each objective 
are provided in Table 12. 
Table 12: 
Objectives and Endpoints (Part C)  
Objectives 
Endpoints 
Primary 
• 
To evaluate the humoral immunogenicity (for 
noninferiority) of mRNA-1010 relative to that 
of a licensed HD seasonal influenza vaccine 
(Fluzone HD) against 4 vaccine-matched 
influenza virus A and B strains at Day 29 in 
adults ≥65 years old. 
• 
GMT at Day 29 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 29 as measured by 
HAI. 
• 
To evaluate the reactogenicity and safety of 
mRNA-1010. 
• 
Frequency and severity of solicited local and 
systemic reactogenicity ARs during a 7-day 
follow-up period postinjection. 
• 
Frequency and severity of any unsolicited 
AEs during the 28-day follow-up period 
postinjection. 
• 
Frequency of any SAEs, MAAEs, AESIs, and 
AEs leading to discontinuation from Day 1 to 
Day 181/EoS. 
Secondary 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 (for superiority) relative to a 
licensed HD seasonal influenza vaccine 
(Fluzone HD) against vaccine-matched 
influenza A and B strains at Day 29. 
• 
GMT at Day 29 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 29 as measured by 
HAI. 
• 
To further evaluate the humoral 
immunogenicity of each study arm against 
vaccine-matched influenza A and B strains at 
Day 29. 
• 
The proportion of participants with HAI titer 
≥1:40 at Day 29. 
• 
GMFR comparing Day 29 to Day 1 
(Baseline) as measured by HAI. 
Exploratory (May be Performed) 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed HD 
seasonal influenza vaccine (Fluzone HD) 
against vaccine-matched influenza virus A and 
B strains at Day 181/EoS in a subset of 
participants. 
• 
GMT at Day 181 as measured by HAI. 
• 
Proportion of participants reaching 
seroconversion at Day 181 as measured by 
HAI. 

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Objectives 
Endpoints 
• 
To evaluate the humoral immunogenicity of 
mRNA-1010 relative to that of a licensed HD 
seasonal influenza vaccine (Fluzone HD) 
against vaccine-matched or vaccine-
mismatched A and B strains. 
• 
GMT and GMFR of nAbs by assays such as 
MN assays or alternative methods against 
vaccine-matched/mismatched strains on Day 
29 compared with Day 1 (Baseline). 
• 
GMT and GMFR of anti-HA antibodies as 
measured by HAI against vaccine-
mismatched strains on Day 29 compared with 
Day 1 (Baseline). 
Abbreviations: AE = adverse event; AESI = adverse event of special interest; AR = adverse reaction; EoS = end of 
study; GMFR = geometric mean fold rise; GMT = geometric mean titer; HA = hemagglutinin; 
HAI = hemagglutination inhibition; HD = high dose; MAAE = medically attended adverse event; 
MN = microneutralization; mRNA = messenger ribonucleic acid; nAb = neutralizing antibody; SAE = serious 
adverse event 
4.3. 
Study Design (Part C)  
4.3.1. 
Overall Design (Part C)  
mRNA-1010-P303 Part C is a Phase 3, randomized, stratified, observer-blind, active-controlled 
study to evaluate the immunogenicity, reactogenicity, and safety of mRNA-1010 seasonal 
influenza vaccine in adults ≥65 years old. 
mRNA-1010 to be tested contains 4 mRNAs in an equivalent mRNA mass ratio that encode 
membrane-bound HA of the 4 different influenza strains recommended by the WHO for 
2023-2024 NH cell- or recombinant-based vaccines. Fluzone HD Quadrivalent contains 4 HAs 
of the 4 different influenza strains recommended by the WHO for 2023-2024 NH egg-based 
vaccines. 
Medically stable adults (see Part C Exclusion Criterion # 3), ≥65 years old, will be screened and 
enrolled. A complete list of inclusion and exclusion criteria is provided in Section 4.4. 
Approximately 3000 participants will be randomly assigned (see Section 4.6) to treatment in this 
study in a 1:1: ratio to 1 of 2 treatment groups to receive either a single dose of mRNA-1010 or a 
single dose of a licensed HD seasonal influenza vaccine (Fluzone HD Quadrivalent, Table 13). 
Table 13: 
Treatment Groups and Dose Levels (Part C)  
Treatment 
Group 
Study Intervention 
Received 
mRNA/Antigen 
Total Dose 
(µg) 
Number of 
Participants 
HA (each) (µg) 
5 
mRNA-1010 
12.5 (of mRNA) 
50 (of mRNA) 
1500 
6 
Active Comparator 
(Fluzone HD Quadrivalent) 
60 (of protein) 
240 (of protein) 1500 
Abbreviations: HA = hemagglutinin; HD = high dose; mRNA = messenger ribonucleic acid 
Table 11 displays the study SoA. Clinic/in-person visits will consist of a Screening Visit (up to 
28 days before the Day 1 Visit and may be performed over multiple visits if within the 28-day 
screening window), a dosing visit on Day 1 (Baseline; may be on the same day as the Screening 
Visit), a visit on Day 29 (Month 1), and a subsequent visit on Day 181 (Month 6)/EoS (in a 

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subset of ~1000 participants) with up to 7 months of study participation for each participant. 
There will also be contacts by electronic means or telephone calls on Day 8, Day 91 (Month 3) 
and Day 181 (Month 6 [non-subset participants]). 
All participants will provide blood samples for assessment of GMT, GMFR, and seroconversion, 
as measured by HAI (Table 11 and Section 4.8.2). Table 11 displays the time periods for 
collecting solicited ARs via eDiary (Section 4.8.3.4) and unsolicited AEs. MAAEs, SAEs, 
AESIs, and AEs leading to discontinuation will be collected from Day 1 to Day 181 
(Month 6)/EoS. 
There may be situations in which the Investigator asks a participant to report for an unscheduled 
visit following the report of an AE. The eCRF should be completed for each unscheduled visit. 
This is an observer-blind study (refer to Section 4.6.1 for details). The Investigator may unblind 
in the event of an emergency (refer to Section 4.5.2.7 for details).  
An IST and CEAC will be involved (refer to Section 5.1.6 for details). 
4.3.2. 
Scientific Rationale for Study Design  
Part C of this study aims to demonstrate noninferiority of mRNA-1010 versus a licensed high 
dose seasonal influenza vaccine (Fluzone HD) in the immune response for all 4 strains, as 
measured by GMT and by seroconversion rate, in adults ≥65 years. 
Because of increased morbidity and mortality associated with influenza infections in older 
adults, Fluzone HD Quadrivalent vaccine is one of 3 influenza vaccines (along with Flublok 
Quadrivalent and Fluad Quadrivalent) that is preferentially recommended for people 65 years 
and older. The Sponsor conducted a Phase 1/2 study which suggested immune responses were on 
par with immune responses to Fluzone HD. 
The rationale for using HAI as a surrogate endpoint of prevention of influenza illness and its 
complications is based on the established precedent of using HA-based immunologic correlates 
for clinical assessment and licensure of influenza vaccines (DHHS 2007a, DHHS 2007b, 
Dunning et al 2016, European Medicines Agency 2016). 
4.3.3. 
Justification for Dose  
The Sponsor has completed a Phase 1/2 study of mRNA-1010 (mRNA-1010-P101, 
NCT04956575) at dose levels up to 200 µg and is now conducting three Phase 3 studies at a 
50 µg dose level: mRNA-1010-P301, a safety and immunogenicity study (NCT05415462), 
mRNA-1010-P302, a safety and efficacy study (NCT05566639), and mRNA-1010-P303 Part A 
(NCT05827978). No safety concerns were identified with dose levels up to 200 µg. The 50-µg 
dose was chosen for the Phase 3 studies based on the observed reactogenicity and 
immunogenicity profile (refer to Section 1.2 for details). 
4.3.4. 
End of Study Definition  
See Section 2.3.4 for details. 

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4.4. 
Study Population (Part C)  
Prospective approval of protocol deviations to recruitment and enrollment criteria, also known as 
protocol waivers or exemptions, is not permitted. 
4.4.1. 
Inclusion Criteria (Part C)  
Participants are eligible to be included in the study only if all of the following criteria apply: 
Age 
1. At least 65 years of age or older, at the time of signing the ICF. 
Type of Participant and Disease Characteristics 
2. Investigator has assessed that the participant understands and is willing and 
physically able to comply with protocol mandated follow-up, including all 
procedures. 
Sex and Contraceptive/Barrier Requirements 
3. A participant AFAB is eligible to participate if they are postmenopausal or a person 
of nonchildbearing potential. 
Informed Consent 
4. Capable of giving signed informed consent as described in Section 5.1.3 which 
includes compliance with the requirements and restrictions listed in the ICF and in 
this protocol. 
4.4.2. 
Exclusion Criteria (Part C)  
Participants are excluded from the study if any of the following criteria apply: 
Medical Conditions 
1. Acutely ill or febrile (temperature ≥38.0℃ [100.4°F]) within 72 hours prior to Day 1. 
Participants meeting this criterion may be rescheduled within the 28-day screening 
window. 
2. Close contact with someone with laboratory-confirmed influenza infection or with 
someone who has been treated with antiviral therapies for influenza (eg, Tamiflu) 
within the past 5 days prior to Day 1. 
3. History of a diagnosis or condition that, in the judgment of the Investigator, is 
clinically unstable or may affect participant safety, assessment of safety endpoints, 
assessment of immune response, or adherence to study procedures. Clinically 
unstable is defined as a diagnosis or condition requiring significant changes in 
management or medication within the 60 days prior to Day 1 and includes ongoing 
workup of an undiagnosed illness that could lead to a new diagnosis or condition. 
• Asymptomatic conditions and conditions with no clinically significant end organ 
involvement (eg, mild hypertension, dyslipidemia) are not exclusionary, if they are 
being appropriately managed and are clinically stable (ie, unlikely to result in 
symptomatic illness within the time course of this study). Illnesses or conditions may 

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be exclusionary, even if otherwise stable, due to therapies used to treat them (eg, 
immune-modifying treatments), at the discretion of the Investigator. 
• Participants who have undergone surgical procedures within 7 days prior to Day 1 or 
are scheduled to undergo a surgical procedure within 28 days after study intervention 
dosing are also excluded. However, minor surgical procedures under local anesthesia 
(eg, excision of skin lesion) or diagnostic procedures (eg, colonoscopy) are allowed. 
4. Reported history of congenital or acquired immunodeficiency, immunosuppressive 
condition or immune-mediated disease, asplenia, or recurrent severe infections. The 
following conditions are permitted at the discretion of the Investigator: 
• Participants who are HIV positive and on antiviral therapy with cluster of 
differentiation 4 count ≥350 cells/mm3 and HIV RNA ≤500 copies/mL within the past 
12 months. 
• Participants with immune-mediated diseases which are stable (eg, Hashimoto’s 
thyroiditis and type 1 diabetes) or conditions such as asthma, psoriasis, vitiligo, gout, 
alopecia areata, or auto-immune ovarian failure, which do not require systemic 
immunosuppressants per Part C Exclusion Criterion # 13. 
5. Dermatologic conditions that could affect local solicited AR assessments (eg, tattoos; 
psoriasis patches affecting skin over the deltoid areas). 
6. Participant has tested positive for influenza by local health authority-approved testing 
methods within 180 days prior to Day 1. 
7. Reported history of anaphylaxis or severe hypersensitivity reaction after receipt of 
mRNA vaccines or any components of the mRNA-1010 or influenza vaccines, including 
egg protein. 
8. Reported history of coagulopathy or bleeding disorder that is considered a 
contraindication to IM injection or phlebotomy. 
9. Malignancy within the previous 2 years (excluding nonmelanoma skin cancer). 
10. History of myocarditis, pericarditis, or myopericarditis within 180 days prior to Day 1 or 
have not returned to Baseline clinical status. Participants who have not returned to 
Baseline after their convalescent period will also be excluded. 
11. History of Guillain-Barre syndrome after any influenza vaccine. 
12. Any medical, psychiatric, or occupational condition, including reported history of drug or 
alcohol abuse, that, in the opinion of the Investigator, might pose additional risk due to 
participation in the study or could interfere with the interpretation of study results. 
Prior/Concomitant Therapy 
13. Participant has received systemic immunosuppressants or immune modifying drugs that 
may impact the immune response for >14 days in total within 180 days prior to Day 1 
(for corticosteroids, ≥10 mg/day of prednisone or equivalent) or is anticipating the need 
for systemic immunosuppressive treatment at any time during participation in the study. 
Inhaled, nasal, and topical steroids are allowed. Intra-articular and epidural steroid 
injections are not allowed within 28 days before and/or after study intervention dosing. 

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14. Participant has received any vaccine authorized or approved by local health agency 
≤28 days prior to study intervention dosing (Day 1) or plans to receive a vaccine 
authorized or approved by local health agency within 28 days before or after study 
intervention dosing. 
15. Participant has received a licensed seasonal influenza vaccine within 6 months (180 days) 
prior to Day 1. 
16. Participant has participated in any investigational seasonal influenza vaccine study where 
the study vaccine was administered within 12 months prior to Day 1. Participants who 
were previously enrolled in mRNA-1010-P303 Part A are not eligible to participate in 
Part C. 
17. Participant is not aware whether they have received an influenza vaccine since September 
2022. 
18. Participant has been treated with antiviral therapies for influenza (eg, Tamiflu) within 
180 days prior to Day 1. 
19. Participant has received systemic immunoglobulins or blood products within 90 days 
prior to Day 1 or plans to receive systemic immunoglobulins or blood products during the 
study. In addition, participants who have received long-acting biological therapies that 
affect immune responses (eg, infliximab) within 90 days prior to Day 1, or plan to receive 
them, are also excluded. 
20. Participant has donated ≥450 mL of blood products within 28 days prior to Day 1 or 
plans to donate blood products during the study. 
Other Exclusion Criteria 
21. Participant has participated in an interventional clinical study within 28 days prior to 
Day 1, based on the medical history interview or plans to do so while participating in this 
study. Participants may continue in prior interventional study follow-up activities, as long 
as it does not involve further investigational treatment other than the study intervention 
described in this protocol (Note: interventions such as counseling, biofeedback, and 
cognitive therapy are not exclusionary). 
22. Participant is working or has worked as study personnel or is an immediate family 
member or household member of study personnel, study site staff, or Sponsor personnel. 
4.4.3. 
Screen Failures  
See Section 2.4.3 for details. 
4.4.4. 
Criteria for Temporarily Delaying the Day 1 Visit  
See Section 2.4.4 and Section 4.7 for details and refer to SoA for Part C (Table 11). 
4.5. 
Study Intervention(s) and Concomitant Therapy (Part C)  
Study intervention(s) refers to the mRNA-1010 vaccine and to the licensed HD seasonal 
influenza vaccine (Fluzone HD) intended to be administered to the study participants during the 
study conduct. 

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4.5.1. 
Study Intervention(s) Administered  
The study intervention(s) to be administered and the treatment groups in the study are provided 
in Table 14. 
The mRNA-1010 vaccine will be administered as a single 0.5 mL IM injection at an mRNA total 
dose level of 50 µg to participants according to the treatment group assignment. 
The active comparator administered in this study is a licensed HD seasonal influenza vaccine, 
Fluzone HD Quadrivalent administered as a single 0.7 mL IM injection.  
Table 14: 
Study Intervention(s) Administered  
Intervention Label 
mRNA-1010.4 
Fluzone HD 
Treatment Group 
Type 
Experimental 
Active comparator 
Intervention Name 
mRNA-1010 
Fluzone HD Quadrivalent 
Intervention 
Description 
mRNA-1010 contains LNP dispersion 
encoding the seasonal influenza vaccine 
antigens, HAs, from the strains 
recommended by the WHO for 2023 to 
2024 NH cell or recombinant-based 
vaccines. 
All mRNAs are formulated in LNPs 
composed of 4 lipids and provided as a 
sterile liquid for injection, white-to-off 
white dispersion in appearance, at a 
concentration of 0.10 mg/mL in 20 mM 
Tris buffer with 87 g/L sucrose, and 
2.2 mM sodium acetate at pH 7.5. 
Licensed high dose quadrivalent 
seasonal vaccine. 
Fluzone HD Quadrivalent contains the 
seasonal influenza vaccine antigens, 
HAs, from the strains recommended by 
the WHO for 2023 to 2024 NH 
egg-based vaccines. 
Type 
Vaccine 
Vaccine 
Dosage Level(s) 
50 µg of mRNA 
Single dose 
240 µg of proteins 
Single dose  
Route of 
Administration 
IM 
IM 
Use 
Experimental 
Active control 
IMP and AxMP 
IMP 
IMP 
Sourcing 
By Sponsor 
By Sponsor 
Packaging and 
Labeling 
The study intervention will be prepared, 
packaged, and labeled in accordance with 
the standard operating procedures of 
ModernaTX, Inc. or those of its designee, 
CFR Title 21, GMP guidelines, ICH and 
GCP guidelines, guidelines for Quality 
System Regulations, and applicable 
regulations. 
The study intervention will be prepared, 
packaged, and labeled in accordance 
with the standard operating procedures 
of ModernaTX, Inc. or those of its 
designee, CFR Title 21, GMP 
guidelines, ICH and GCP guidelines, 
guidelines for Quality System 
Regulations, and applicable regulations. 

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Abbreviations: AxMP = auxiliary medicinal product; CFR = Code of Federal Regulations; GCP = Good Clinical 
Practice; GMP = Good Manufacturing Practice; HA = hemagglutinin; HD = high dose; ICH = International 
Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use; 
IM = intramuscular(ly); IMP = investigational medicinal product; LNP = lipid nanoparticle; mRNA = messenger 
ribonucleic acid; NH = Northern Hemisphere; WHO = World health Organization. 
4.5.2. 
Preparation, Handling, Storage, and Accountability  
See Section 2.5.2 for details. 
4.5.2.1. 
Study Intervention(s) Preparation  
The study intervention will be prepared for each participant based on their treatment group 
assignment. The mRNA-1010 vaccine will be administered as a single 0.5 mL IM injection and 
will contain mRNA-1010 at a dose of 50 µg. The licensed HD seasonal influenza vaccine 
(Fluzone HD) will be administered at a volume of 0.7 mL. The mRNA-1010 and the licensed 
HD seasonal influenza vaccine (Fluzone HD Quadrivalent) preparation instructions are detailed 
in the Pharmacy Manual. 
4.5.2.2. 
Study Intervention(s) Administration  
The study intervention (mRNA-1010) or the licensed HD seasonal influenza vaccine (Fluzone 
HD Quadrivalent) will be administered as a single IM injection into the deltoid muscle on Day 1. 
Preferably, the study intervention should be administered into the nondominant arm. 
Participants will be monitored for a minimum of 30 minutes after administration of the study 
intervention. Assessments will include vital sign measurements and monitoring for solicited ARs 
as shown in the SoA (Table 11). 
The clinic will be appropriately staffed with individuals with basic cardiopulmonary 
resuscitation training/certification. Either onsite resuscitation equipment and personnel or 
appropriate protocols for the rapid transport of a participant to a resuscitation area or facility are 
required. 
Further instructions for the preparation and administration of mRNA-1010 and licensed HD 
seasonal influenza vaccine (Fluzone HD Quadrivalent) are described in the Pharmacy Manual. 
4.5.2.3. 
Study Intervention(s) Packaging and Labeling  
See Section 2.5.2.3 for details. 
4.5.2.4. 
Study Intervention(s) Storage  
mRNA-1010 must be stored at the clinical site at 2°C to 8°C in a secure area with limited access 
and must be protected from moisture and light until it is prepared for administration 
(Section 4.5.2.1). The refrigerator should have automated temperature recording and a 24-hour 
alert system in place that allows for rapid response in case of refrigerator malfunction. The 
refrigerator should be connected to a backup generator. In addition, for study intervention 
accountability, staff are required to keep a temperature log to establish a record of compliance 
with these storage conditions. The clinic is responsible for reporting any study intervention that 
was not temperature controlled during shipment or storage. Such study intervention will be 
retained for inspection by the monitor and disposed of according to approved methods. Please 

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note that mRNA-1010 will be stored at -25°C to - 15°C at the depots and during shipments to the 
clinical sites. 
The licensed HD seasonal influenza vaccine (Fluzone HD Quadrivalent) should be stored in its 
original container and in accordance with the instructions in the Pharmacy Manual. 
4.5.2.5. 
Study Intervention(s) Accountability  
See Section 2.5.2.5 for details. 
4.5.2.6. 
Study Intervention(s) Handling and Disposal  
See Section 2.5.2.6 for details. 
4.5.2.7. 
Unblinding  
See Section 2.5.2.7 for details. 
4.6. 
Assignment to Study Intervention (Part C)  
Randomization will be performed using an IRT. Approximately 3000 participants will be 
randomly assigned to treatment in this study in a 1:1 ratio to 1 of 2 treatment groups to receive 
either a single dose of mRNA-1010 or a single dose of a licensed HD seasonal influenza vaccine 
(Fluzone HD Quadrivalent, Table 14). Randomization will be stratified by the previous flu 
season (since September 2022) vaccination status (received or not received; if received, was it 
from prior participation in the mRNA-1010-P302 study [yes/no]).  
4.6.1. 
Blinding  
See Section 2.6.1 for details. 
4.6.2. 
Study Intervention Compliance  
See Section 2.6.2 for details. 
4.6.3. 
Dose Modification  
Not applicable. 
4.6.4. 
Continued Access to Study Intervention After the End of the Study  
See Section 2.6.4 for details. 
4.6.5. 
Treatment of Overdose  
See Section 2.6.5 for overdose. 
4.6.6. 
Prior and Concomitant Therapy  
See Section 2.6.6 for details. 
4.6.6.1. 
Prohibited Therapy  
See Section 2.6.6.1 for details. 

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4.6.6.2. 
Recording of Concomitant Medications, Concomitant Vaccinations and 
Concomitant Procedures  
See Section 2.6.6.2 for details. 
4.6.6.3. 
Concomitant Medications and Vaccines That May Lead to the Elimination of a 
Participant From Per-protocol Analyses  
See Section 2.6.6.3 for details. 
4.7. 
Discontinuation of Study Intervention and Participant 
Discontinuation/Withdrawal (Part C)  
Discontinuation of specific sites or of the study as a whole are detailed in Section 5.1.10. 
4.7.1. 
Discontinuation of Study Intervention  
Not applicable. 
4.7.2. 
Participant Discontinuation/Withdrawal from the Study  
See Section 2.7.1.1 for details and refer to SoA for Part C (Table 11). 
4.7.3. 
Lost to Follow-up  
See Section 2.7.1.2 for details. 
4.7.4. 
Pause Rules  
Not applicable. 
4.8. 
Study Assessments and Procedures (Part C)  
See Section 2.8 for details and refer to SoA for Part C (Table 11). 
4.8.1. 
Demography  
See Section 2.8.1 for details. 
4.8.2. 
Immunogenicity Assessments  
Planned timepoints for all immunogenicity assessments are provided in the SoA for Part C 
(Table 11). 
The following analytes will be measured: 
• Serum antibody level as measured by HAI assay. 
• Serum neutralizing antibody level as measured by microneutralization assay or 
similar methods may also be performed. 
Measurement of antibody levels will be performed in a laboratory designated by the Sponsor. 

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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 influenza vaccines, 
additional assay development, and the immune response across influenza viruses. 
4.8.3. 
Safety Assessments  
See Section 2.8.3 for details and refer to SoA for Part C (Table 11). 
4.8.3.1. 
Physical Examinations  
See Section 2.8.3.1 for details and refer to SoA for Part C (Table 11). 
4.8.3.2. 
Vital Signs  
See Section 2.8.3.2 for details and refer to SoA for Part C (Table 11). 
4.8.3.3. 
Safety Phone Calls  
See Section 2.8.3.5 and refer to SoA for Part C (Table 11). 
4.8.3.4. 
Use of Electronic Diaries  
See Section 2.8.3.6 for details and refer to SoA for Part C (Table 11). 
4.8.3.5. 
Ancillary Supplies for Participant Use  
See Section 2.8.3.7 for details and refer to SoA for Part C (Table 11). 
4.8.3.6. 
AEs, SAEs, and Other Safety Reporting  
The definitions of AEs, SAEs, solicited ARs, and unsolicited AEs can be found in Section 5.3. 
See Section 2.8.3.8 for details. 
4.8.3.6.1. Time Period and Frequency for Collecting AE and SAE Information  
See Section 2.8.3.8.1 for details. 
4.8.3.6.2. Method of Detecting AEs and SAEs  
See Section 2.8.3.8.2 for details and refer to SoA for Part C (Table 11). 
4.8.3.6.3. Follow-up of AEs and SAEs  
See Section 2.8.3.8.3 for details and refer to SoA for Part C (Table 11). 
4.8.3.6.4. Regulatory Reporting Requirements for SAEs  
See Section 2.8.3.8.4 for details. 
4.8.3.6.5. Pregnancy  
Not applicable. 

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4.8.3.7. 
Solicited Adverse Reactions  
See Section 2.8.3.9 for details and refer to SoA for Part C (Table 11). 
4.8.3.8. 
Medically Attended Adverse Events  
The definition of MAAE is provided in Section 5.3.3. 
4.8.3.9. 
Adverse Events of Special Interest  
The definition of AESI is provided in Section 5.3.4. AESIs for this protocol are listed in 
Section 5.3. 
4.8.3.9.1. Anaphylaxis  
See Section 2.8.3.11.1 for details. 
4.8.3.9.2. Myocarditis and/or Pericarditis  
See Section 2.8.3.11.2 for details. 
4.8.4. 
Pharmacokinetics  
Pharmacokinetic parameters are not evaluated in this study. 
4.8.5. 
Pharmacodynamics  
Pharmacodynamic parameters are not evaluated in this study. 
4.8.6. 
Genetics  
N/A. 
4.8.7. 
Biomarkers  
N/A. 
4.8.8. 
Immunogenicity Assessments  
See Section 2.8.8 for details and refer to SoA for Part C (Table 11). 
4.8.9. 
Health Economics or Medical Resource Utilization and Health Economics  
Health economics or medical resource utilization and health economics parameters are not 
evaluated in this study. 
4.9. 
Statistical Considerations (Part C)  
See Section 2.9 for details. 
4.9.1. 
Blinding and Responsibility for Analyses  
See Section 2.9.1 and Section 4.9.6 for details. 

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4.9.2. 
Statistical Hypotheses  
The primary objective in Part C is to evaluate the noninferiority of the immunogenicity response 
to mRNA-1010 versus the licensed Fluzone HD Quadrivalent, as measured by GMT and 
seroconversion rate at Day 29 using HAI assay, for all 4 vaccine-matched influenza virus A and 
B strains:  
• For each of the 4 vaccine-matched strains, the noninferiority hypothesis in terms of 
the GMT is: 
Null hypothesis:                 H01:  GMR ≤0.667 (inferior) vs. 
Alternative hypothesis:      Ha1:  GMR >0.667 (noninferior) 
using a noninferiority margin of 1.5, where the GMR is the ratio of the GM HAI titer 
in the mRNA-1010 group compared with the GM HAI titer in the Fluzone HD 
Quadrivalent group. 
• For each of the 4 vaccine-matched strains, the noninferiority hypothesis in 
seroconversion rate is: 
Null hypothesis:                 H02: SCR difference ≤ -10% (inferior) vs. 
Alternative hypothesis:      Ha2:  SCR difference > -10% (noninferior) 
using a noninferiority margin of 10%, where the SCR difference is the difference in 
the SCR between the mRNA-1010 group compared with the Fluzone HD 
Quadrivalent group. 
The noninferiority hypotheses in the GMT and SCR will be evaluated for all 4 strains and Part C 
is considered a study success if all the 8 coprimary immunogenicity endpoints meet the 
noninferiority criteria. Therefore, each of the coprimary immunogenicity endpoints will be tested 
at 1-sided alpha of 0.025 level:  
• For each strain, the noninferiority in GMT will be demonstrated by the lower bound 
of the 95% CI of the GMR ruling out 0.667, ie, the lower bound of the 95% 
CI >0.667. 
• For each strain, the noninferiority in SCR will be demonstrated by the lower bound of 
the 95% CI of the SCR difference ruling out −10%, ie, the lower bound of the 95% 
CI >−10%. 
Upon successful demonstration of noninferiority for Part B, ie, the noninferiority success criteria 
have been met for all 8 coprimary immunogenicity endpoints, the following superiority 
hypotheses will be tested: 
• For each of the 4 vaccine-matched strains, the superiority hypothesis in terms of the 
GMT at Day 29 is: 
Null hypothesis:                 H03:  GMR = 1 vs. 
Alternative hypothesis:      Ha3:  GMR >1 (superior) 

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• For each of the 4 vaccine-matched strains, the superiority hypothesis in 
seroconversion rate at Day 29 is: 
Null hypothesis:                 H04: SCR difference = 0 vs. 
Alternative hypothesis:      Ha4:  SCR difference >0 (superior) 
The multiplicity adjustment procedures for the superiority tests of the 8 immunogenicity 
endpoints are specified in Section 4.9.7 (also see Figure 1 in Section 3.9.7). 
4.9.3. 
Sample Size Determination  
Assuming approximately 15% of 3000 randomized participants will be excluded from the PP 
Immunogenicity Set, with approximately 2550 participants in the PP Immunogenicity Set 
(1:1 ratio; approximately 1275 participants in each group):  
• The study has at least 99% power to meet the noninferiority success criteria in GMT 
for all 4 strains at a 1-sided alpha of 0.025 level with a noninferiority margin of 1.5. 
An underlying GMR (mRNA-1010 vs. the licensed Fluzone HD Quadrivalent 
vaccine) of 0.90 is assumed for each of the 4 strains and the standard deviation of the 
natural log-transformed levels is assumed to be 1.5. 
• The study has at least 93% power to meet the noninferiority success criteria in SCR 
for all 4 strains, at a 1-sided alpha of 0.025 level with a noninferiority margin of 10%. 
The SCRs of 58% for influenza A strains and SCRs of 48% for influenza B strains, 
respectively, are assumed in the mRNA-1010 group, whereas the SCRs in the 
licensed Fluzone HD Quadrivalent group are assumed to be 60% and 50% for the 
influenza A and B strains, respectively. 
The overall power for achieving the primary noninferiority objective in Part C would be 
approximately 93%. Furthermore, the sample size provides 1) an approximately 79.5% power for 
a superiority test of GMT for an individual strain with an underlying GMR (mRNA-1010 vs. 
Fluzone HD Quadrivalent) of 1.2; 2) an approximately 43% power for a superiority test of SCR 
for an A strain (assuming an SCR of 64% for mRNA-1010 vs. 60% for Fluzone HD 
Quadrivalent), and an approximately 41% power for a superiority test of SCR for a B strain 
(assuming an SCR of 54% for mRNA-1010 vs 50% for Fluzone HD Quadrivalent) at 2-sided 
alpha of 0.025 (with alpha split for multiplicity adjustment). 
4.9.4. 
Analysis Sets  
See Section 2.9.4 for details. 
4.9.5. 
Statistical Analyses  
See Section 2.9.5 for details. 
4.9.5.1. 
Immunogenicity Analyses  
The immunogenicity analyses will be conducted for Part C separately. See Section 2.9.5.1 for 
details. 

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4.9.5.2. 
Adverse Events  
See Section 2.9.5.2 for details. 
4.9.5.3. 
Exploratory Analyses  
Exploratory analyses will be described in the SAP before database lock. 
4.9.6. 
Planned Analyses  
4.9.6.1. 
Primary Analyses  
The primary analysis of safety and immunogenicity for Part C will be performed after all 
participants have completed the Day 29 visit. All data relevant to the primary study analysis 
through the Day 29 visit will be cleaned for the primary analysis (ie, data that are as clean as 
possible) and a report may be generated. 
The analysis will be performed by a separate team of unblinded programmers and statisticians. 
More details can be found in the study data blinding plan.  
4.9.6.2. 
Final Analysis  
Final analysis of all safety and immunogenicity data for Part C will be performed once all 
participants complete the Day 181 (Month 6)/EoS Visit. 
4.9.7. 
Multiplicity  
No multiplicity adjustment will be applied for the primary noninferiority objective because Part C is 
successful only if all the 8 coprimary immunogenicity endpoints meet the noninferiority criteria. Each 
of the coprimary immunogenicity endpoints will be tested at 1-sided alpha of 0.025 level. 
Upon successful demonstration of the noninferiority, the superiority hypotheses specified in 
Section 4.9.2 will be tested following the prespecified order of the superiority tests (see 
Section 3.9.7 and Figure 1 for details). 

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5. 
SUPPORTING DOCUMENTATION AND OPERATIONAL 
CONSIDERATIONS  
5.1. 
Appendix 1: Regulatory, Ethical, and Study Oversight 
Considerations  
5.1.1. 
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. 
• Protocols and any substantial amendments to the protocol will require health 
authority approval prior to initiation 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. 
5.1.2. 
Financial Disclosure  
Investigators and Subinvestigators will provide the Sponsor with sufficient, accurate financial 
information as requested to allow the Sponsor to submit complete and accurate financial 
certification or disclosure statements to the appropriate regulatory authorities. Investigators are at 
minimum responsible for providing information on financial interests during the course of the 
study and for 1 year after completion of the study. 

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5.1.3. 
Informed Consent Process  
• The Investigator or the Investigator’s representative will explain the nature of the 
study, including the risks and benefits, to the potential participant and answer all 
questions regarding the study. 
• Potential participants must be informed that their participation is voluntary. They will 
be required to sign a statement of informed consent that meets the requirements of 
21 CFR 50, local regulations, ICH guidelines, privacy and data protection 
requirements, where applicable, and the IRB or study center. 
• The medical record must include a statement that written informed consent was 
obtained before the participant was enrolled in the study and the date the written 
consent was obtained. The authorized person obtaining the informed consent must 
also sign the ICF. 
• Participants must be reconsented to the most current version of the ICF(s) during their 
participation in the study. 
• A copy of the ICF(s) must be provided to the participant. 
A participant who is rescreened is not required to sign another ICF if the rescreening occurs 
within 28 days from the previous ICF signature date. 
There will be separate consents that address the samples for optional exploratory research. The 
Investigator or authorized designee will explain to each participant the objectives of the 
exploratory research. Participants will be told that they are free to refuse to participate and may 
withdraw their consent at any time and for any reason during the storage period. 
5.1.4. 
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 study. These 
include, but are not limited to, services that provide a means to identify potential participants and 
direct them to participating clinical study sites, participant support services such as concierge, 
and study information and support collateral for both the participant and the site. Advertisements 
to be used for the recruitment of study participants, and any other written information regarding 
this study to be provided to the participant should be submitted to the Sponsor for approval. All 
documents must be approved by the IRB. 
5.1.5. 
Data Protection  
• Participants will be assigned a unique identifier by the Sponsor. Any participant 
records or datasets that are transferred to the Sponsor will contain the identifier only; 
participant names or any information which would make the participant identifiable 
will not be transferred. 
• The participant must be informed that their personal study-related data will be used 
by the Sponsor in accordance with local data protection law. The level of disclosure 

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must also be explained to the participant who will be required to give consent for 
their data to be used as described in the informed consent. 
• The participant must be informed that their medical records may be examined by 
Clinical Quality Assurance auditors or other authorized personnel appointed by the 
Sponsor, by appropriate IRB members, and by inspectors from regulatory authorities. 
• The contract between the Sponsor or designee and the study sites may specify 
responsibilities of the parties related to data protection, including handling of data 
security breaches and respective communication and cooperation of the parties. 
• Information technology systems used to collect, process, and store study-related data 
are secured by technical and organizational security measures designed to protect 
such data against accidental or unlawful loss, alteration, or unauthorized disclosure or 
access. 
5.1.6. 
Committee Structure  
5.1.6.1. 
Internal Safety Team  
An IST will be formed to review primary and cumulative blinded and unblinded safety data on a 
regular basis. 
5.1.6.2. 
Cardiac Event Adjudication Committee  
An independent CEAC comprised of medically qualified personnel, including cardiologists, will 
review all reported cases of myocarditis, pericarditis, and myopericarditis to determine if they 
meet CDC criteria for “probable” or “confirmed” events (Gargano et al 2021). Any cases that the 
CEAC assesses as representing probable or confirmed cases of myocarditis, pericarditis, or 
myopericarditis will be referred to the Sponsor, who will then determine if additional action is 
needed. The CEAC operates under the rules of an approved charter, details regarding the CEAC 
composition, responsibilities, procedures, and frequency of data review are defined in the 
charter. 
5.1.7. 
Dissemination of Clinical Study Data  
ModernaTX, Inc. shares information about clinical studies and results on publicly accessible 
websites, based on international and local legal and regulatory requirements, and other clinical 
study disclosure commitments established by pharmaceutical industry associations. These 
websites include clinicaltrials.gov, EU clinicaltrialregister (eu.ctr), etc., as well as some national 
registries. 
5.1.8. 
Data Quality Assurance  
• All participant data relating to the study will be recorded in eCRFs. The Investigator 
is responsible for verifying that data entries are accurate and correct by physically or 
electronically signing the eCRF. 
• Guidance on completion of eCRFs will be provided in eCRF Completion Guidelines. 

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• The Investigator must permit study-related monitoring, audits, IRB review, and 
regulatory agency inspections and provide direct access to source documents. 
• QTLs will be predefined to identify systematic issues that can impact participant 
safety and/or reliability of study results. These predefined parameters will be 
monitored during the study, and important deviations from the QTLs and remedial 
actions taken will be summarized in the CSR. 
• Monitoring details describing strategy, including definition of study critical data 
items and processes (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 onsite monitoring) are provided 
in the monitoring plan. 
• The Sponsor or designee is responsible for the data management of this study, 
including quality checking of the data. 
• The Sponsor assumes accountability for actions delegated to other individuals (eg, 
contract research organizations). 
• Records and documents, including signed ICFs, pertaining to the conduct of this 
study must be retained by the Investigator for 2 years after the last marketing 
application approval or, if not approved, 2 years following the discontinuance of the 
test article for investigation unless local regulations or institutional policies require a 
longer retention period. 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. 
5.1.9. 
Source Documents  
• 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 site. 
• Data 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. 
• Definition of what constitutes source data and its origin can be found in Data 
Agreements and Monitoring Plan. 
• The Investigator must maintain accurate documentation (source data) that supports 
the information entered in the eCRF. 
• The Sponsor or designee will perform monitoring to confirm that data entered into the 
eCRF by authorized clinic staff 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. 

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5.1.10. 
Study and Site Start Closure  
First Act of Recruitment 
The study start date is the date on which the clinical study will be open for recruitment of participants. 
The first act of recruitment is the first site open and will be the study start date. 
Study/Site Termination 
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. 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. 
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: 
For study termination: 
• Discontinuation of further study intervention development. 
For site termination: 
• 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 or no recruitment (evaluated after a reasonable amount of time) of 
participants by the Investigator. 
• Total number of participants included earlier than expected. 
If the study is prematurely terminated or suspended, the Sponsor shall promptly inform the 
investigators, the IRB, the regulatory authorities, and any contract research organization(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. 
5.1.11. 
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 
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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5.2. 
Appendix 2: Clinical Laboratory Tests  
The tests detailed in Table 15 will be performed by a laboratory by local and the central 
laboratories.  
Local laboratory results are only required in the event that the central laboratory results are not 
available in time for either study intervention administration and/or response evaluation. If a 
local sample is required, it is important that the sample for central analysis is obtained at the 
same time. Additionally, if the local laboratory results are used to make either a study 
intervention decision or response evaluation, the results must be recorded. 
Additional tests may be performed at any time during the study as determined necessary by the 
Investigator or required by local regulations. 
Protocol-specific requirements for inclusion or exclusion of participants are detailed in 
Section 2.4 for Part A, Section 3.4 for Part B, and Section 4.4 for Part C of the protocol. 
Investigators must document their review of each laboratory safety report. 
Table 15: 
Protocol-required Safety Laboratory Tests  
Laboratory Tests 
Parameters 
Pregnancy Testing 
• Highly sensitive serum or urine hCG pregnancy test (as needed for 
POCBP)a 
Other Screening Tests 
• Follicle-stimulating hormone and estradiol (as needed for PONCBP) 
Abbreviations: hCG = human chorionic gonadotropin; POCBP = person of childbearing potential; PONCBP: person 
of nonchildbearing potential 
a. 
Local urine testing will be standard for the protocol unless serum testing is required by local regulation or IRB. 

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5.3. 
Appendix 3: AEs and SAEs: Definitions and Procedures for 
Recording, Evaluating, Follow-up, and Reporting  
5.3.1. 
Definition of AE  
AE Definition 
An AE is any untoward medical occurrence in a clinical study participant, temporally associated 
with the use of study intervention, whether or not considered related to the study intervention. 
NOTE: An AE can therefore be any unfavorable and unintended sign (including an abnormal 
laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use 
of study intervention. 
Events Meeting the AE Definition 
• Any abnormal laboratory (hematology, clinical chemistry, or urinalysis) or diagnostic 
(eg, electrocardiogram, radiological scans, vital signs measurements) test results or 
physical examination finding, including those that worsen from Baseline, considered 
clinically significant in the medical and scientific judgment of the Investigator. 
• Exacerbation of a chronic or intermittent pre-existing condition including either an 
increase in frequency and/or intensity of the condition. 
• New condition detected or diagnosed after study intervention administration even 
though it may have been present before the start of the study. 
• Signs, symptoms, or the clinical sequelae of a suspected drug-drug interaction. 
• Signs, symptoms, or the clinical sequelae of a suspected overdose of either study 
intervention or a concomitant medication. Overdose per se will not be reported as an 
AE/SAE unless it is an intentional overdose taken with possible suicidal/self-harming 
intent. Such overdoses should be reported regardless of sequelae. 
Events not Meeting the Adverse Event Definition 
• Medical or surgical procedure (eg, endoscopy, appendectomy): the condition that 
leads to the procedure is the AE. 
• Situations in which an untoward medical occurrence did not occur (social and/or 
convenience admission to a hospital). 
• Anticipated day-to-day fluctuations of pre-existing disease(s) or condition(s) present 
or detected at the start of the study that do not worsen. 
Definition of Unsolicited and Solicited AE 
An unsolicited AE is an AE that was not solicited using a participant diary and that is 
communicated by a participant who has signed the informed consent. Unsolicited AEs include 
serious and nonserious AEs. 
Solicited AEs are predefined local (at the injection site) and systemic events for which the 
participant is specifically questioned, and which are noted by the participant in their eDiary. 

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5.3.2. 
Definition of SAE  
An SAE is defined as any untoward medical occurrence that, at any dose, meets one or more of 
the criteria listed: 
a. Results in death 
b. Is life-threatening 
The term life-threatening in the definition of serious refers to an event in which the 
participant was at risk of death at the time of the event. It does not refer to an event, which 
hypothetically might have caused death, if it were more severe. 
c. 
Requires inpatient hospitalization or prolongation of existing hospitalization 
In general, hospitalization signifies that the participant has been admitted (usually involving 
at least an overnight stay) at the hospital or emergency ward for observation and/or 
treatment that would not have been appropriate in the physician’s office or outpatient 
setting. Complications that occur during hospitalization are AEs. If a complication prolongs 
hospitalization or fulfills any other serious criteria, the event is serious. When in doubt as to 
whether hospitalization occurred or was necessary, the AE should be considered serious. 
NOTE: Hospitalization for elective treatment of a pre-existing condition that did not worsen 
from Baseline is not considered an AE. 
d. Results in persistent or significant disability/incapacity 
The term disability means a substantial disruption of a person’s 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. 
e. 
Is a congenital anomaly/birth defect 
f. 
Is an important medical event 
Medical or scientific judgment should be exercised by the Investigator in deciding whether 
SAE reporting is appropriate in other situations such as important medical events that may 
not be immediately life-threatening or result in death or hospitalization but may jeopardize 
the participant or may 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 events include invasive or malignant cancers, intensive treatment in 
an emergency room or at home for allergic bronchospasm, blood dyscrasias, or 
convulsions not resulting in hospitalization. 
5.3.3. 
Definition of MAAE  
A MAAE is an AE that leads to an unscheduled visit to a healthcare practitioner. This would 
include visits to a study site for unscheduled assessments not required per protocol (eg, rash 
assessment, abnormal laboratory follow-up) and visits to healthcare practitioners external to the 
study site (eg, emergency room, urgent care, primary care physician). 

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An unscheduled visit for assessment of protocol-defined ILI (symptoms assessment and NP 
swab) is not considered a MAAE unless additional medical evaluation, including 
examinations/testing not required per protocol, and/or treatment is provided during the visit. 
5.3.4. 
Definition of AESI  
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 are required. Such events may require further investigation to 
characterize and understand them. 
The AESIs defined for this protocol can be found in Section 5.3.4. 
5.3.5. 
Recording and Follow-up of AE and/or SAE  
AE and SAE Recording 
• When an AE/SAE occurs, it is the responsibility of the Investigator to review all 
documentation (eg, hospital progress notes, laboratory reports, and diagnostics 
reports) related to the event and then record all relevant AE/SAE information in EDC. 
• There may be instances when copies of medical records are requested by the Sponsor 
or designee. In this case, all participant identifiers, with the exception of the 
participant number, will be redacted on the copies of the medical records before 
submission to the Sponsor or designee. It is not acceptable for the Investigator to send 
photocopies of the participant’s medical records to the Sponsor or designee in lieu of 
completion of the eCRF/required form. 
• The Investigator will attempt to establish at least a provisional diagnosis of the event 
based on signs, symptoms, and/or other clinical information. Whenever possible, the 
diagnosis (not the individual signs/symptoms) will be documented as the AE/SAE. 
Assessment of Intensity 
The Investigator will make an assessment of intensity for each AE and SAE reported during the 
study and assign it to one of the following categories:  
• Mild: 
Usually transient and may require only minimal treatment or therapeutic intervention. 
The event does not generally interfere with activities of daily living. 
• Moderate:  
Usually alleviated with additional specific therapeutic intervention. The event 
interferes with activities of daily living, causing discomfort but poses no significant 
or permanent risk of harm to the research participant. 
• Severe:  
Interrupts activities of daily living, or significantly affects clinical status, or may 
require intensive therapeutic intervention. 
The Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventive 
Vaccine Clinical Trials (DHHS 2007b) will be used to categorize local and systemic 
reactogenicity events (solicited ARs), clinical laboratory test results, and vital sign measurements 
observed during this study. The intensity grading scale used in this study is presented in Table 16. 

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Table 16: 
Adult and Adolescent Solicited Adverse Reactions and Grades  
Reaction 
Grade 0 
(None) 
Grade 1 
(Mild) 
Grade 2 
(Moderate) 
Grade 3 
(Severe) 
Grade 4 
(Life-threatening) 
Local 
Injection site pain 
None 
No interference 
with activity  
Some 
interference 
with activity  
Prevents daily 
activity 
Requires emergency 
room visit or 
hospitalization 
Injection site 
erythema (redness) 
<25 mm/ 
<2.5 cm 
25-50 mm/ 
2.5-5 cm 
51-100 mm/ 
5.1-10 cm 
>100 mm/ 
>10 cm 
Necrosis or 
exfoliative 
dermatitis 
Injection site 
swelling/induration 
(hardness) 
<25 mm/ 
<2.5 cm 
25-50 mm/ 
2.5-5 cm 
51-100 mm/ 
5.1-10 cm  
>100 mm/ 
>10 cm 
Necrosis  
Axillary 
(underarm) 
swelling or 
tenderness 
ipsilateral to the 
side of injection 
None 
No interference 
with activity 
Some 
interference 
with activity 
Prevents daily 
activity 
Requires emergency 
room visit or 
hospitalization 
Systemic 
Headache 
None 
No interference 
with activity 
Some 
interference 
with activity 
Prevents daily 
activity 
Requires emergency 
room visit or 
hospitalization 
Fatigue 
None 
No interference 
with activity  
Some 
interference 
with activity 
Prevents daily 
activity  
Requires emergency 
room visit or 
hospitalization 
Myalgia 
(muscle aches all 
over body) 
None 
No interference 
with activity  
Some 
interference 
with activity 
Prevents daily 
activity  
Requires emergency 
room visit or 
hospitalization 
Arthralgia 
(joint aches in 
several joints) 
None 
No interference 
with activity  
Some 
interference 
with activity 
Prevents daily 
activity  
Requires emergency 
room visit or 
hospitalization 

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Reaction 
Grade 0 
(None) 
Grade 1 
(Mild) 
Grade 2 
(Moderate) 
Grade 3 
(Severe) 
Grade 4 
(Life-threatening) 
Nausea/vomiting 
None 
No interference 
with activity or 
1-2 episodes/ 
24 hours 
Some 
interference 
with activity 
or 
>2 episodes/2
4 hours 
Prevents daily 
activity, 
requires 
outpatient 
intravenous 
hydration 
Requires emergency 
room visit or 
hospitalization for 
hypotensive shock 
Chills 
None 
No interference 
with activity 
Some 
interference 
with activity 
not requiring 
medical 
intervention 
Prevents daily 
activity and 
requires 
medical 
intervention 
Requires emergency 
room visit or 
hospitalization 
Fever (oral) 
<38.0°C 
<100.4°F 
38.0-38.4°C 
100.4-101.1°F 
38.5-38.9°C 
101.2-102.0°F 
39.0-40.0°C 
102.1-104.0°F 
>40.0°C 
>104.0°F 
Note: Events listed above but starting >7 days poststudy intervention dosing will be recorded in the eCRF. Causality 
for each event will be determined per assessment by the Investigator. 
Modified from the Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventive 
Vaccine Clinical Trials (DHHS 2007b). 
Assessment of Causality 
• The Investigator must assess the relationship between study intervention and each 
occurrence of each AE/SAE, based on clinical judgment, and document this in the 
source document and EDC. 
• Not related: There is not a reasonable possibility of a relationship to the study 
intervention. Participant did not receive the study intervention OR temporal sequence 
of the AE onset relative to administration of the study intervention is not reasonable 
OR the AE is more likely explained by another cause than the study intervention. 
• Related: There is a reasonable possibility of a relationship to the study intervention. 
There is evidence of exposure to the study intervention. The temporal sequence of the 
AE onset relative to the administration of the study intervention is reasonable. The 
AE is more likely explained by the study intervention than by another cause. 
• There may be situations in which the Investigator has minimal information 
concerning an AE; however, an assessment of causality must be provided by the 
Investigator at the time of reporting to the Sponsor or designee based on their clinical 
understanding of the event, knowledge of the study intervention, and current 
information available. 
Follow-up of AEs and SAEs 
The Investigator is obligated to perform or arrange for the conduct of supplemental 
measurements and/or evaluations as medically indicated or as requested by the Sponsor or 

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designee to elucidate the nature and/or causality of the AE or SAE as fully as possible. This may 
include additional laboratory tests or investigations, histopathological examinations, or 
consultation with other health care professionals. 
If a participant dies during participation in the study or during a recognized follow-up period, the 
Investigator will provide the Sponsor or designee with a copy of any postmortem findings 
including histopathology. 
New or updated information will be recorded as revisions to the original report. 
The Investigator will report any updated SAE data to the Sponsor or designee within 24 hours of 
receipt of the information. 
5.3.6. 
Reporting of SAEs/AESI  
Note: AESI will be reported in the same way as SAEs. 
The primary mechanism for reporting an SAE to the Sponsor or designee will be the electronic 
EDC. 
If the electronic system is unavailable, then the site will use the paper SAE data collection tool 
provided by the Sponsor to report the event within 24 hours. 
• SAE reports should be emailed to drugsafety@modernatx.com. 
• The site will enter the SAE data into the electronic system as soon as it becomes 
available. 
NOTE: Initial notification via email or fax does not replace the need for the Investigator 
to complete and sign the electronic SAE data collection tool within the designated 
reporting timeframes. 
After the study is completed at a given site, the EDC tool will be taken offline to prevent the 
entry of new data or changes to existing data. If a site receives a report of a new SAE from a 
study participant or receives updated data on a previously reported SAE after the EDC tool has 
been taken offline, then the site can report this information on a paper SAE form (see next 
section). 

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5.4. 
Appendix 4: Adverse Event of Special Interest  
Investigators should report all events that fall into the categories presented in Table 17 as an 
AESI per the reporting processes in Section 5.3.6. These AESIs are medical concepts that are 
generally of interest in vaccine safety surveillance as per the Brighton Collaboration and Safety 
Platform for Emergency Vaccines or the vaccine platform. 
Table 17: 
Adverse Events of Special Interest  
Medical Concept 
Additional Notes 
Thrombocytopenia 
• 
Platelet counts <125 × 109. 
• 
Including but not limited to immune thrombocytopenia, platelet 
production decreased, thrombocytopenia, thrombocytopenic 
purpura, thrombotic thrombocytopenic purpura, or Hemolysis, 
elevated liver enzymes, low platelet count syndrome. 
New onset of or worsening 
of the following neurologic 
diseases: 
• 
Guillain-Barre Syndrome. 
• 
Acute disseminated encephalomyelitis. 
• 
Idiopathic peripheral facial nerve palsy (Bell’s palsy). 
• 
Seizures including but not limited to febrile seizures and/or 
generalized seizures/convulsions. 
Anaphylaxis 
• 
Anaphylaxis associated with study intervention dosing as defined 
per protocol (Section 2.8.3.11.1). 
• 
Follow reporting procedures in Section 5.3.6. 
Myocarditis/Pericarditis 
• 
Myocarditis. 
• 
Pericarditis. 
• 
Myopericarditis. 

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5.5. 
Appendix 5: CDC Working Case Definitions of Pericarditis, 
Myocarditis, and Myopericarditis Occurring After Receipt of 
COVID-19 mRNA Vaccines  
The CDC Working Case Definitions of probable and confirmed myocarditis, pericarditis, and 
myopericarditis (Gargano et al 2021) are provided in Table 18 as guidance. 
Table 18: 
Case Definitions of Probably 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:* 
• 
Chest pain, pressure, or 
discomfort 
• 
Dyspnea, shortness of breath, or 
pain with breathing 
• 
Palpitations 
• 
Syncope 
Presence of ≥1 new or worsening of the 
following clinical symptoms:* 
• 
Chest pain, pressure, or discomfort 
• 
Dyspnea, shortness of breath, or pain 
with breathing 
• 
Palpitations 
• 
Syncope 
OR, infants and children aged 
<12 years might instead have ≥2 of 
the following symptoms: 
• 
Irritability 
• 
Vomiting 
• 
Poor feeding 
• 
Tachypnea 
• 
Lethargy 
OR, infants and children aged <12 years 
might instead have ≥2 of the following 
symptoms: 
• 
Irritability 
• 
Vomiting 
• 
Poor feeding 
• 
Tachypnea 
• 
Lethargy 
AND 
≥1 new finding of 
• 
Troponin level above upper 
limit of normal (any type of 
troponin). 
• 
Abnormal ECG or EKG or 
rhythm monitoring findings 
consistent with myocarditis§. 
• 
Abnormal cardiac function or 
wall motion abnormalities on 
echocardiogram. 
• 
cMRI findings consistent with 
myocarditis¶. 
AND 
≥1 new finding of 
• 
Histopathologic confirmation of 
myocarditis†. 
• 
cMRI findings consistent with 
myocarditis¶ in the presence of troponin 
level above upper limit of normal (any 
type of troponin). 

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Condition 
Definition 
AND 
• 
No other identifiable cause of 
the symptoms and findings. 
AND 
• 
No other identifiable cause of the 
symptoms and findings. 
Acute 
pericarditis** 
Presence of ≥2 new or worsening of the following clinical features: 
• 
Acute chest pain†† 
• 
Pericardial rub on exam 
• 
New ST-elevation or PR-depression on EKG 
• 
New or worsening pericardial effusion on echocardiogram or MRI 
Myopericarditis 
This term may be used for participants who meet criteria for both myocarditis and 
pericarditis. 
Abbreviations: cMRI = cardiac magnetic resonance imaging; ECG or EKG = electrocardiogram; MRI = magnetic 
resonance imaging. 
* Persons who lack the listed symptoms but who meet other criteria may be classified as subclinical myocarditis 
(probable or confirmed). 
† Using the Dallas criteria (Aretz et al 1987). Autopsy cases may be classified as confirmed clinical myocarditis on 
the basis of meeting histopathologic criteria if no other identifiable cause. 
§ 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. 
Using either the original or the revised Lake Louise criteria. 
https://www.sciencedirect.com/science/article/pii/S0735109718388430?via%3Dihubexternal icon. 
** https://academic.oup.com/eurheartj/article/36/42/2921/2293375external icon. 
†† 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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5.6. 
Appendix 6: Contraceptive and Barrier Guidance  
5.6.1. 
Definitions  
Person of Childbearing Potential  
Persons AFAB in the following categories are considered POCBP (fertile): 
1. Following menarche. 
2. From the time of menarche until becoming postmenopausal unless permanently sterile 
(see below) 
• A postmenopausal state is defined as no menses for 12 months without an 
alternative medical cause. 
− A high FSH level in the postmenopausal range may be used to confirm a 
postmenopausal state in persons not using hormonal contraception or HRT. 
However, in the absence of 12 months of amenorrhea, confirmation with more 
than one FSH measurement is required.  
− Persons on HRT and whose menopausal status is in doubt will be required to use 
one of the non-estrogen hormonal highly effective contraception methods if they 
wish to continue their HRT during the study. Otherwise, they must discontinue 
HRT to allow confirmation of postmenopausal status before study enrollment. 
• Permanent sterilization methods (for the purpose of this study) include: 
− Documented hysterectomy. 
− Documented bilateral salpingectomy. 
− Documented bilateral oophorectomy. 
− For individuals with permanent infertility due to an alternate medical cause other 
than the above, (eg, Mullerian agenesis, androgen insensitivity, gonadal 
dysgenesis), Investigator discretion should be applied to determining study entry. 
Note: Documentation can come from the clinic staff’s review of the participant’s 
medical records, medical examination, or medical history interview. 
• If fertility is unclear (eg, amenorrhea in adolescents or athletes) and a menstrual cycle 
cannot be confirmed before study intervention dosing, additional evaluation should be 
considered. 
Person of Nonchildbearing Potential  
Participants in the following categories are considered PONCBP: 
1. Premenopausal participant with permanent infertility due to one of the following: 
a. Documented hysterectomy. 
b. Documented bilateral salpingectomy. 
c. Documented bilateral oophorectomy. 

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d. For individuals with permanent infertility due to an alternate medical cause other than 
the above, (eg, Mullerian agenesis, androgen insensitivity, gonadal dysgenesis), 
investigator discretion should be applied to determining study entry. 
Note: Documentation can come from the site personnel’s review of the participant’s medical 
records, medical examination, or medical history interview. 
2. Postmenopausal participant 
a. A postmenopausal state is defined as no menses for 12 months without an alternative 
medical cause. 
− A high follicle stimulating hormone (FSH) level in the postmenopausal range may 
be used to confirm a postmenopausal state in participants not using hormonal 
contraception or hormonal replacement therapy (HRT). However, in the absence 
of 12 months of amenorrhea, confirmation with more than one FSH measurement 
is required. 
− Participants on HRT and whose menopausal status is in doubt must discontinue 
HRT to allow confirmation of postmenopausal status before study enrollment. 
5.6.2. 
Contraception Guidance  
CONTRACEPTIVESa ALLOWED DURING THE STUDY INCLUDE: 
Highly Effective Methodsb That Have Low User Dependency Failure rate of <1% per year when 
used consistently and correctly. 
• Implantable progestogen-only hormone contraception associated with inhibition of ovulation.c 
• Intrauterine device. 
• Intrauterine hormone-releasing system.c 
• Bilateral tubal occlusion. 
• Azoospermic partner (vasectomized or due to a medical cause). 
Azoospermia is a highly effective contraceptive method provided that the partner is the sole sexual 
partner of the person of childbearing potential and the absence of sperm has been confirmed. If 
not, an additional highly effective method of contraception should be used. Spermatogenesis cycle 
is approximately 90 days. 
Note: documentation of azoospermia for a participant can come from the clinic staff’s review of 
the participant’s medical records, medical examination, or medical history interview. 
Highly Effective Methodsb That Are User Dependent Failure rate of <1% per year when used 
consistently and correctly. 
Combined (estrogen- and progestogen-containing) hormonal contraception associated with inhibition 
of ovulationc 
− oral 
− intravaginal 
− transdermal 
− injectable 
Progestogen-only hormone contraception associated with inhibition of ovulationc 
− oral 
− injectable 

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CONTRACEPTIVESa ALLOWED DURING THE STUDY INCLUDE: 
Highly Effective Methodsb That Have Low User Dependency Failure rate of <1% per year when 
used consistently and correctly. 
Sexual abstinence 
Sexual abstinence is considered a highly effective method only if defined as refraining from 
heterosexual intercourse during the entire period of risk associated with the study intervention. The 
reliability of sexual abstinence needs to be evaluated in relation to the duration of the study and the 
preferred and usual lifestyle of the participant.) 
Effective Methodsd That Are Not Considered Highly Effective Failure rate of ≥1% per year when 
used consistently and correctly. 
• Progestogen-only oral hormonal contraception where inhibition of ovulation is not the primary 
mode of action. 
• External or internal condom with or without spermicide. 
• Cervical cap, diaphragm, or sponge with spermicide. 
• A combination of external condom with either cervical cap, diaphragm, or sponge with spermicide 
(double-barrier methods).c 
a. Contraceptive use should be consistent with local regulations regarding the use of contraceptive 
methods for those participating in clinical studies. 
b. Failure rate of <1% per year when used consistently and correctly. Typical use failure rates differ 
from those when used consistently and correctly. 
c. Use of external condoms in addition to hormonal contraception is recommended. If locally 
required, in accordance with Clinical Trial Facilitation Group guidelines, acceptable contraceptive 
methods are limited to those which inhibit ovulation as the primary mode of action. 
d. Considered effective, but not highly effective - failure rate of ≥1% per year. 
Note: Periodic abstinence (calendar, symptothermal, postovulation methods), withdrawal (coitus 
interruptus), spermicides only, and lactational amenorrhea method are not acceptable methods of 
contraception. External condom and internal condom should not be used together (due to risk of 
failure from friction). 

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5.7. 
Appendix 7: Protocol Amendment History  
5.7.1. 
Global Amendment 1, 10 Oct 2023:  
This amendment is considered to be substantial. 
Main Rationale for the Amendment: 
The primary analysis results from Part A of this study demonstrated noninferior immunogenicity 
of mRNA-1010 compared to a standard dose (SD) Quadrivalent seasonal influenza vaccine 
(Fluarix Quadrivalent) based on the prespecified success criteria for noninferiority: the lower 
bounds of 95% confidence intervals (CIs) for the geometric mean ratio (GMR) >0.667, and the 
lower bounds of the CIs for seroconversion rate (SCR) difference >-10% for all 4 strains 
(A/H1N1, A/H3N2, B/Victoria, and B/Yamagata). The purpose of adding Part B to this study is 
to further characterize the safety of mRNA-1010 candidate seasonal influenza vaccine in adults 
in the age group of 18 to <65 years old. The purpose of adding Part C to the study is to evaluate 
safety and immunogenicity of mRNA-1010 compared to a licensed high dose (HD) Quadrivalent 
seasonal influenza vaccine (Fluzone HD) in adults ≥65 years old. 
Summary of Changes in Protocol Amendment 1: 
Section # and Name 
Description of Change 
Brief Rationale 
Title Page, Signature Page, 
Protocol Amendment Summary of 
Changes, Header 
Updated the brief title, and 
protocol version and date, as 
applicable. 
To align with all parts of 
the study (Part A, B, and C) 
and to reflect the current 
version. 
Section 1 (Protocol Summary) and 
Section 2 (Introduction) 
Section 2 (Introduction) was 
moved to the beginning as 
Section 1. 
Section 1 (Protocol Summary) was 
changed to Section 2.1 under Part 
A (Section 2). 
To align the Introduction 
with all parts of the study 
(Part A, B, and C). 
Section 1.1 (Protocol Synopsis), 
Section 1.2 (Schema), and Section 
1.3 (Schedule of Activities 
Section 1.1 was changed to 
Section 2.1.1. 
Section 1.2 was deleted. 
Section 1.3 was changed to 
Section 2.1.2) under Part A. 
To reorganize as protocol 
summary for Part A. 
Section 2.3.2, Benefit Assessment 
New Section 1.3.2, Removed NP 
swab testing from statement, 
“Participant will obtain 
information about their general 
health status through the medical 
evaluations/assessments associated 
with this study (ie, physical 
examination, vital signs 
measurement, NP swab testing).” 
NP swab testing is no 
longer required in newly 
added Part B and Part C. 

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Section # and Name 
Description of Change 
Brief Rationale 
Section 5.3 (Screen Failures) 
New Section 2.4.3, Removed 
statement regarding retaining 
initially assigned participant 
numbers: 
Individuals who do not meet the 
criteria for participation in this 
study (screen failure) may be 
rescreened one time and will retain 
their initially assigned participant 
number. 
To correct an error in the 
original protocol. 
Sections 3 to 9 
Changed: Section 3 (Objectives 
and Endpoints) to Section 2.2; 
Section 4 (Study Design) to 
Section 2.3; Section 5 (Study 
Population) to Section 2.4; Section 
6 (Study Intervention and 
Concomitant Therapy) to Section 
2.5; Section 6.3 (Assignment to 
Study Intervention) to Section 2.6; 
Section 7 (Discontinuation of 
Study Intervention and Participant 
Discontinuation/Withdrawal) to 
Section 2.7; Section 8 (Study 
Assessments and Procedures) to 
Section 2.8; Section 9 (Statistical 
Considerations) to Section 2.9 
under Part A. 
To reorganize the study 
procedures under Part A. 
Section 10 and Section 11 
Section 10 (Supporting 
Documentation and Operational 
Considerations) was changed to 
Section 5, and Section 11 
(References) was changed to 
Section 6. 
To align these sections with 
all 3 parts of the study (Part 
A, B, and C). 
Section 2.8.3 (Safety Assessment) 
Added pregnancy testing to Part A. To correct an omission in 
the original protocol. 
Section 2.9.6.1 (Primary Analysis)  Added Part A to the sentence. 
To align the primary 
analysis with Part A of the 
study. 
Section 2.9.6.2 (Final Analysis) 
Added Part A to the sentence. 
To align the final analysis 
with Part A of the study. 

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Section # and Name 
Description of Change 
Brief Rationale 
New Section 3 (Part B) 
Added a new section (Part B) to 
further evaluate the safety and 
reactogenicity of mRNA-1010 
against the licensed standard dose 
influenza vaccine, Fluarix SD, in 
adults 18 to <65 years old. 
To further evaluate the 
safety of mRNA-1010 
against the licensed 
standard dose influenza 
vaccine, Fluarix SD, in 
adults 18 to <65 years old. 
New Section 4 (Part C) 
Added a new section (Part C) to 
evaluate the immunogenicity, 
reactogenicity, and safety of 
mRNA-1010 against the licensed 
high dose influenza vaccine, 
Fluzone HD, in adults ≥65 years 
old. 
To evaluate the 
immunogenicity and safety 
of mRNA-1010 against the 
licensed high dose 
influenza vaccine, Fluzone 
HD, in adults ≥65 years 
old. 
Section 5.6.1 (Definitions) 
Added definition for Person of 
Nonchildbearing Potential 
(PONCBP) 
To align with inclusion 
criteria # 3 of Part C. 
 

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6. 
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