Trial · NCT04649151

A Study to Evaluate the Safety, Reactogenicity, and Effectiveness of mRNA-1273 Vaccine in Adolescents 12 to <18 Years Old to Prevent COVID-19

NCT04649151, Phase 2, Phase 3, Completed, ModernaTX, Inc.; results first posted 2025-09-15

3 sourcestrials-2026-11-12-0.5.0

Cite this record

ConductScience Library. A Study to Evaluate the Safety, Reactogenicity, and Effectiveness of mRNA-1273 Vaccine in Adolescents 12 to <18 Years Old to Prevent COVID-19. Trials, record NCT04649151. Release trials-2026-11-12-0.5.0, 12 Nov 2026. https://conductscience.org/library/trials/NCT04649151

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Trial

As registered on ClinicalTrials.gov, in the graph's capture of the registry.

Title: A Study to Evaluate the Safety, Reactogenicity, and Effectiveness of mRNA-1273 Vaccine in Adolescents 12 to <18 Years Old to Prevent COVID-19
NCT number: NCT04649151
Status: Completed
Phases: Phase 2, Phase 3
Enrollment: 4,328 participants, actual
Lead sponsor: ModernaTX, Inc.
Conditions: SARS-CoV-2
Interventions: mRNA-1273, Placebo, mRNA-1273.222
First posted: 2020-12-02
Last updated: 2025-09-15
Other registries' IDs: eudract:2023-000382-14
Results first posted: 2025-09-15
Limitations and caveats: Part 1C-2 enrollment discontinued before planned number of participants. Part 2 discontinued early due to availability of updated variant vaccine (mRNA-1273.222); no hypothesis testing done for primary endpoint/other endpoints not assessed.

Source ClinicalTrials.gov

Registered outcomes26

Each outcome the trial registered, primary first, in ClinicalTrials.gov's words.

List	Outcome	Time frame	Description
Primary	Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	7 days post-vaccination	Solicited ARs (local and systemic) were collected in an electronic diary (eDiary). Local ARs included injection site pain, injection site erythema (redness), injection site swelling/induration (hardness), and axillary (underarm) swelling or tenderness ipsilateral to the side of injection. Systemic ARs included fever, headache, fatigue, myalgia, arthralgia, nausea/vomiting, and chills. Solicited ARs considered causally related to injection were graded 1-4 (per Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventive Vaccine Clinical Trials); lower score indicated lower severity, and higher score indicated greater severity. Investigator reviewed if the solicited AR was recorded as an adverse event (AE) as detailed in the AE section. A Summary of serious AEs (SAEs) and nonserious AEs ("Other"), regardless of causality, is located in the AE section.
Primary	Number of Participants With Unsolicited AEs	Up to 28 days post-vaccination	An unsolicited AE was any AE reported by the participant that was not specified as a solicited AR in the protocol or was specified as a solicited AR but started outside the protocol-defined period for reporting solicited ARs (onset after Day 7 of dosing). An AE was defined as any untoward medical occurrence associated with the use of a drug in humans, whether or not considered drug related. Any abnormal laboratory test result or other safety assessment, including one that worsened from baseline and was considered clinically significant by the Investigator was recorded as an AE. Non-serious SARs persisting beyond 7 days, leading to discontinuation, or medically attended were classified as AEs in Part 1/2 but not in Part 3. COVID-19/SARS-CoV-2 infections were AEs in Part1/2 but were considered clinical events for efficacy in Part 3 and not AEs. A Summary of SAEs and nonserious AEs ("Other"), regardless of causality, is located in the AE section.
Primary	Part 1A Geometric Mean Value of Serum Pseudovirus Neutralizing Antibody (nAb) ID50 Titers From Study P203 Vaccine Recipients at Day 57 Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	Day 57 Study P203/Day 57 Study P301	Pseudovirus nAb ID50 titers were measured using pseudovirus neutralization assay (PsVNA) assay. Antibody values reported as below the lower limit of quantification (LLOQ) were replaced by 0.5\*LLOQ. Values greater than the upper limit of quantification (ULOQ) were replaced by the ULOQ if actual values were not available (LLOQ: 18.5 arbitrary units (AU)/milliliter (mL), ULOQ: 45118 AU/mL). Antibody levels were analyzed using an analysis of covariance (ANCOVA) model with the group variable (adolescents in P203 and young adults in P301) as fixed effect. PPIS P301: randomly selected participants from Study P301 aged 18-25 meeting pre-specified criteria were used for comparison assessments of immune response.
Primary	Part 1A Seroresponse Rate (SRR) for Serum Pseudovirus nAb ID50 in Study P203 Vaccine Recipients at Day 57 Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	Day 57 Study P203/Day 57 Study P301	Percentage of participants with seroresponse for pseudovirus nAb ID50 measured using PsVNA assay are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4\*LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ (LLOQ: 18.5 AU/mL), ULOQ: 45118 AU/mL). PPIS P301: randomly selected participants from Study P301 aged 18-25 meeting pre-specified criteria were used for comparison assessments of immune response.
Primary	Part 1C-1 Geometric Mean Concentration (GMC) of Serum Pseudovirus nAb Against the Original Strain After the BD in Study P203 at BD Day 29 Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	BD Day 29 Study P203/Day 57 Study P301	Pseudovirus nAb were measured using PsVNA assay. Antibody values reported as below the LLOQ were replaced by 0.5\*LLOQ. Values greater than the ULOQ were replaced by the ULOQ if actual values were not available (LLOQ: 10, ULOQ: 281600). PPIS P301: randomly selected participants from study P301 aged 18-25 meeting pre-specified criteria and SARS-CoV-2 negative were used for comparison assessments of immune response.
Primary	Part 1C-1 SRR of Serum Pseudovirus nAb Against the Original Strain After the BD in Study P203 at BD Day 29 Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	BD Day 29 Study P203/Day 57 Study P301	Percentage of participants with seroresponse for pseudovirus nAb measured using PsVNA assay are reported. Seroresponse relative to pre-Dose 1 (baseline) at a participant level was defined as a change from below the LLOQ to equal or above 4 \* LLOQ, or at least a 4-fold-rise if baseline was equal to or above LLOQ (LLOQ: 10 AU/mL, ULOQ: 281600 AU/mL). PPIS P301: randomly selected participants from Study P301 aged 18-25 meeting pre-specified criteria and SARS-CoV-2 negative were used for comparison assessments of immune response.
Primary	Part 3 GMC of nAb Post Dose 1 mRNA 1273.222 Against Omicron BA.4/BA.5 Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	Day 29 Study P203/Day 57 Study P301	Antibody values reported as below the LLOQ were replaced by 0.5\*LLOQ. Values greater than the ULOQ were replaced by the ULOQ if actual values were not available (LLOQ: 103 AU/mL, ULOQ: 28571 AU/mL). ANCOVA model with the group variable (adolescents in P203 and young adults in P301) as fixed effect. PPIS P301: randomly selected participants from Study P301 aged 18-25 meeting pre-specified criteria and SARS-CoV-2 negative were used for comparison of immune response.
Primary	Part 1C-2 GMC of Post-booster Pseudovirus nAb Against Ancestral Strain at BD Day 29	BD Day 29	Antibody values reported as below the LLOQ were replaced by 0.5 \* LLOQ. Values greater than the ULOQ were replaced by the ULOQ if actual values were not available (LLOQ: 10 AU/mL, ULOQ: 111433 AU/mL).
Primary	Part 2 GMC of the Pseudovirus nAb Against Ancestral Strain at Day 57	Day 57	Antibody values reported as below the LLOQ were replaced by 0.5 \* LLOQ. Values greater than the ULOQ were replaced by the ULOQ if actual values were not available (LLOQ: 10 AU/mL, ULOQ: 111433 AU/mL).
Primary	Part 3 GMC of nAb Post Dose 1 mRNA 1273.222 Against SARS-CoV-2 Ancestral Strain Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	Day 29 Study P203/Day 57 Study P301	Antibody values reported as below the LLOQ were replaced by 0.5\*LLOQ. Values greater than the ULOQ were replaced by the ULOQ if actual values were not available (LLOQ: 10 AU/mL, ULOQ: 111433 AU/mL). ANCOVA model with the group variable (adolescents in P203 and young adults in P301) as fixed effect. PPIS P301: randomly selected participants from Study P301 aged 18-25 meeting pre-specified criteria and SARS-CoV-2 negative were used for comparison of immune response.

1 to 10 of 26Source ClinicalTrials.gov

See all 26 registered outcomes

Outcomes26

Each outcome the trial posted results for, in ClinicalTrials.gov's words.

Type	Outcome	Time frame	Population	Units	Measured as
PRIMARY	Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	7 days post-vaccination	Solicited Safety Set included participants who received at least 1 dose of study drug and contributed any solicited AR data.	Participants	COUNT_OF_PARTICIPANTS
PRIMARY	Number of Participants With Unsolicited AEs	Up to 28 days post-vaccination	Safety Set: participants who received at least 1 dose of study drug. As prespecified in the protocol, Part 1B was not assessed for this outcome measure. 'Overall number of participants analyzed' = participants evaluable for this endpoint.	Participants	COUNT_OF_PARTICIPANTS
PRIMARY	Part 1A Geometric Mean Value of Serum Pseudovirus Neutralizing Antibody (nAb) ID50 Titers From Study P203 Vaccine Recipients at Day 57 Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	Day 57 Study P203/Day 57 Study P301	Part 1A PPIS: randomized participants who were selected for the Immunogenicity Subset, received planned doses of study drug per schedule, complied with immunogenicity testing schedule, and had no major protocol deviations that impacted key or critical data. Participants who were seropositive at baseline were excluded from the PPIS. 'Overall number of participants analyzed' = participants evaluable for this endpoint.	titer	GEOMETRIC_MEAN
PRIMARY	Part 1A Seroresponse Rate (SRR) for Serum Pseudovirus nAb ID50 in Study P203 Vaccine Recipients at Day 57 Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	Day 57 Study P203/Day 57 Study P301	Part 1A PPIS: randomized participants who were selected for the Immunogenicity Subset, received planned doses of study drug per schedule, complied with immunogenicity testing schedule, and had no major protocol deviations that impacted key or critical data. Participants who were seropositive at baseline were excluded from the PPIS. 'Overall number of participants analyzed' = participants evaluable for this endpoint.	percentage of participants	NUMBER
PRIMARY	Part 1C-1 Geometric Mean Concentration (GMC) of Serum Pseudovirus nAb Against the Original Strain After the BD in Study P203 at BD Day 29 Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	BD Day 29 Study P203/Day 57 Study P301	Part 1C-1 PPIS-Neg: participants were baseline (pre-dose 1 of part 1A) SARS-CoV-2 negative, had BD-Day 1 and BD-Day 29 Ab assessment, had no major protocol deviations, did not receive off-study COVID-19 vaccination prior to BD-Day 29 visit, received 2 doses of mRNA-1273 in the Blinded Phase per schedule, received BD, and were pre-booster SARS-CoV2 negative. 'Overall number of participants analyzed' = participants evaluable for this endpoint.	arbitrary units (AU)/mL	GEOMETRIC_MEAN
PRIMARY	Part 1C-1 SRR of Serum Pseudovirus nAb Against the Original Strain After the BD in Study P203 at BD Day 29 Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	BD Day 29 Study P203/Day 57 Study P301	Part 1C-1 PPIS-Neg: participants were baseline (pre-dose 1 of part 1A) SARS-CoV-2 negative, had BD-Day 1 and BD-Day 29 Ab assessment, had no major protocol deviations, did not receive off-study COVID-19 vaccination prior to BD-Day 29 visit, received 2 doses of mRNA-1273 in the Blinded Phase per schedule, received BD, and were pre-booster SARS-CoV2 negative. 'Overall number of participants analyzed' = participants evaluable for this endpoint.	percentage of participants	NUMBER
PRIMARY	Part 3 GMC of nAb Post Dose 1 mRNA 1273.222 Against Omicron BA.4/BA.5 Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	Day 29 Study P203/Day 57 Study P301	Part 3 PPIS-Pos: participants received Dose 1 of mRNA-1273.222, had Day 29 antibody assessments, no major protocol deviations, did not receive off-study COVID-19 vaccination prior to Day 29, SARS-CoV-2 positive at Baseline. 'Overall number of participants analyzed' = participants evaluable for the endpoint.	AU/mL	GEOMETRIC_MEAN
PRIMARY	Part 1C-2 GMC of Post-booster Pseudovirus nAb Against Ancestral Strain at BD Day 29	BD Day 29	Part 1C-2 PPIS: all randomized participants who received BD in Part 1C-2, had BD-Day 29 Ab assessment, had no major protocol deviations that impacted key or critical data, and did not receive off-study COVID-19 vaccination prior to BD-Day 29 visit. 'Overall number of participants analyzed' = participants evaluable for this endpoint.	AU/mL	GEOMETRIC_MEAN
PRIMARY	Part 2 GMC of the Pseudovirus nAb Against Ancestral Strain at Day 57	Day 57	Part 2 PPIS: all randomized participants who received at least 1 dose of the planned study drug, had Ab assessment for the analysis endpoint, and had no major protocol deviations that could impact key or critical data.	AU/mL	GEOMETRIC_MEAN
PRIMARY	Part 3 GMC of nAb Post Dose 1 mRNA 1273.222 Against SARS-CoV-2 Ancestral Strain Compared With Those From Young Adult (18 to 25 Years of Age) Vaccine Recipients (Day 57) in Study P301	Day 29 Study P203/Day 57 Study P301	Part 3 PPIS-Pos: participants received Dose 1 of mRNA-1273.222, had Day 29 antibody assessments, no major protocol deviations, did not receive off-study COVID-19 vaccination prior to Day 29, SARS-CoV-2 positive at Baseline. 'Overall number of participants analyzed' = participants evaluable for the endpoint.	AU/mL	GEOMETRIC_MEAN

1 to 10 of 26Source ClinicalTrials.gov

See all 26 outcomes

Results by group143

Each measurement the trial posted, group by group, in the words and numbers it posted.

Outcome	Group	Category	Value	Units
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	Part 1A: mRNA-1273 100 μg	Grade 1	586	Participants
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	Part 1A: Placebo	Grade 1	585	Participants
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	Part 1C-1: mRNA-1273 50 µg BD	Grade 1	627	Participants
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	Part 1C-2: mRNA-1273 50 μg BD	Grade 1	42	Participants
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	Part 2: mRNA-1273 50 μg First Injection	Grade 1	25	Participants
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	Part 2: mRNA-1273 50 μg Second Injection	Grade 1	18	Participants
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	Part 2: mRNA-1273 50 μg BD	Grade 1	7	Participants
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	Part 3: mRNA-1273.222 50 μg 1 Dose	Grade 1	145	Participants
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	Part 1A: mRNA-1273 100 μg	Grade 2	1250	Participants
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)	Part 1A: Placebo	Grade 2	293	Participants

1 to 10 of 143Source ClinicalTrials.gov

See all 143 results by group

Participant flow90

How many started, completed or left each group, period by period.

Period	Milestone	Group	Participants
Overall Study	STARTED	Part 1A: mRNA-1273 100 μg	2,490
Overall Study	STARTED	Part 1A: Placebo	1,243
Overall Study	STARTED	Part 1C-2: mRNA-1273 50 μg Booster Dose (BD)	155
Overall Study	STARTED	Part 2: mRNA-1273 50 μg	52
Overall Study	STARTED	Part 3: mRNA-1273.222 50 µg	388
Overall Study	Part 1: 1st Injection	Part 1A: mRNA-1273 100 μg	2,486
Overall Study	Part 1: 1st Injection	Part 1A: Placebo	1,240
Overall Study	Part 1: 1st Injection	Part 1C-2: mRNA-1273 50 μg Booster Dose (BD)	0
Overall Study	Part 1: 1st Injection	Part 2: mRNA-1273 50 μg	0
Overall Study	Part 1: 1st Injection	Part 3: mRNA-1273.222 50 µg	0

1 to 10 of 90Source ClinicalTrials.gov

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Adverse events612

Each adverse event the trial posted, group by group: the participants affected out of those at risk.

Type	Event	Organ system	Group	Affected	At risk	Events
other	Abdominal pain	Gastrointestinal disorders	Part 1A: mRNA-1273 100 μg	8	2,486	9
other	Abdominal pain	Gastrointestinal disorders	Part 1A: Placebo	3	1,240	3
other	Abdominal pain	Gastrointestinal disorders	Part 1B: mRNA-1273 100 µg	0	96	0
other	Abdominal pain	Gastrointestinal disorders	Part 1C-1: mRNA-1273 50 µg BD	6	1,408	6
other	Abdominal pain	Gastrointestinal disorders	Part 1C-2: mRNA-1273 50 μg BD	0	155	0
other	Abdominal pain	Gastrointestinal disorders	Part 2: mRNA-1273 50 μg	0	52	0
other	Abdominal pain	Gastrointestinal disorders	Part 2: mRNA-1273 50 ug BD	1	19	1
other	Abdominal pain	Gastrointestinal disorders	Part 3: mRNA1273.222 50 µg 1 Dose	1	388	1
other	Abdominal pain	Gastrointestinal disorders	Part 3: mRNA-1273.222 50 ug Second Dose	1	335	1
other	Injection site lymphadenopathy	General disorders	Part 1A: mRNA-1273 100 μg	137	2,486	146

1 to 10 of 612Source ClinicalTrials.gov

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Adverse event totals27

The totals the trial posted for each group.

Total	Group	Affected	At risk
Total, all-cause mortality	Part 1A: mRNA-1273 100 μg	0	2,486
Total, all-cause mortality	Part 1A: Placebo	0	1,240
Total, all-cause mortality	Part 1B: mRNA-1273 100 µg	0	96
Total, all-cause mortality	Part 1C-1: mRNA-1273 50 µg BD	0	1,408
Total, all-cause mortality	Part 1C-2: mRNA-1273 50 μg BD	0	155
Total, all-cause mortality	Part 2: mRNA-1273 50 μg	0	52
Total, all-cause mortality	Part 2: mRNA-1273 50 ug BD	0	19
Total, all-cause mortality	Part 3: mRNA1273.222 50 µg 1 Dose	0	388
Total, all-cause mortality	Part 3: mRNA-1273.222 50 ug Second Dose	1	335
Total, other adverse events	Part 1A: mRNA-1273 100 μg	943	2,486

1 to 10 of 27Source ClinicalTrials.gov

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Papers2

The papers the trial lists on ClinicalTrials.gov.

PMID	Listed as	Source
34379915	DERIVED	PubMed
39332418	DERIVED	PubMed

Grants0

The grants NIH RePORTER links to the trial, newest funded first: NIH's, and some of AHRQ's, CDC's, FDA's and VA's. Each shows its title, principal investigators, organization and funder in its newest year.

None in this release.

Trial comparisons4

Comparisons of the trial's two groups, calculated by ConductScience from the counts it posted.

Comparison	Source
Part 1A: mRNA-1273 100 μg vs Part 1A: Placebo: Part 1A Number of Participants With a First Occurrence of Symptomatic COVID-19	Trial comparisons
Part 1A: mRNA-1273 100 μg vs Part 1A: Placebo: Part 1A Number of Participants With Asymptomatic SARS-CoV-2 Infection	Trial comparisons
Part 1A: mRNA-1273 100 μg vs Part 1A: Placebo: Part 1A Number of Participants With a SARS-CoV-2 Infection (Symptomatic or Asymptomatic)	Trial comparisons
Part 1A: mRNA-1273 100 μg vs Part 1A: Placebo: Part 1A Number of Participants With Secondary Case Definition of COVID-19 (Center for Disease Control and Prevention [CDC] Case Definition)	Trial comparisons

Tests0

The ConductCognition tests this trial's registered outcomes name, as ScienceGraph matched them in trial-tests-2026-11-12-0.2.1.

None in this release.

Data dates

The day each source was copied for this release.

ClinicalTrials.gov: 2026-11-12; ClinicalTrials.gov
Results, from AACT: 2026-03-23; AACT
NIH grant links: 2026-11-13; NIH RePORTER

Sources 3

ClinicalTrials.gov's posted results, through CTTI's AACTFreely available. Acknowledgement requested
ClinicalTrials.govNo license stated
NIH RePORTER's clinical studies and project filesPublic domain

Each source's terms

ClinicalTrials.gov's posted results, through CTTI's AACTClinicalTrials.gov data via Aggregate Analysis of ClinicalTrials.gov (AACT), CTTI. CTTI makes its materials freely available and requests acknowledgement. https://aact.ctti-clinicaltrials.org/documentation/299
ClinicalTrials.govnone stated
NIH RePORTER's clinical studies and project filesPublic domain (NIH RePORTER)

ClinicalTrials.gov's data carry an international copyright outside the United States: https://clinicaltrials.gov/about-site/terms-conditions.

For software

Read this trial from software.

The record and each of its lists are JSON, twenty rows a page. No key.

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GET https://conductscience.org/api/trials/v1/NCT04649151/registered?page=2

API reference For AI assistants