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Clinical Trial Results:
A Phase 2, Randomized, Observer-blind Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of mRNA-1345, an mRNA Vaccine Targeting Respiratory Syncytial Virus, in Children 2 to <18 Years of Age at High Risk of Respiratory Syncytial Virus Disease

Summary
EudraCT number	2024-000502-15
Trial protocol	Outside EU/EEA
Global end of trial date	27 Aug 2025

Results information
Results version number	v1(current)
This version publication date	14 Mar 2026
First version publication date	14 Mar 2026
Other versions

Trial Information
Subject Disposition
Baseline Characteristics
End Points
Adverse Events
More Information

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Trial information

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Sponsor protocol code

mRNA-1345-P202

ISRCTN number

US NCT number

NCT06097299

WHO universal trial number (UTN)

Sponsor organisation name

ModernaTX, Inc.

Sponsor organisation address

325 Binney Street, Cambridge, United States, 02142

Public contact

Moderna WeCare Team, ModernaTX, Inc., +1 866-663-3762, WeCareClinicalTrials@modernatx.com

Scientific contact

Moderna WeCare Team, ModernaTX, Inc., +1 866-663-3762, WeCareClinicalTrials@modernatx.com

Is trial part of an agreed paediatric investigation plan (PIP)

Does article 45 of REGULATION (EC) No 1901/2006 apply to this trial?

Does article 46 of REGULATION (EC) No 1901/2006 apply to this trial?

Yes

Analysis stage

Final

Date of interim/final analysis

27 Aug 2025

Is this the analysis of the primary completion data?

Yes

Primary completion date

27 Aug 2025

Global end of trial reached?

Yes

Global end of trial date

27 Aug 2025

Was the trial ended prematurely?

Main objective of the trial

The primary objective of Cohort 1 and Cohort 2 Part A was to evaluate the safety and reactogenicity of a single study injection. The primary objective of Cohort 1 Part B was to evaluate the incidence of respiratory syncytial virus (RSV)-associated respiratory tract disease (RSV-RTD) during 6 months after re-enrollment.

Protection of trial subjects

This study was conducted in accordance with the protocol and consensus ethical principles derived from international guidelines including the Declaration of Helsinki, Council for International Organizations of Medical Sciences (CIOMS) International Ethical Guidelines, applicable International Council for Harmonisation (ICH) Good Clinical Practice (GCP) Guidelines, and other applicable laws and regulations.

Background therapy

Evidence for comparator

Actual start date of recruitment

24 Oct 2023

Long term follow-up planned

Independent data monitoring committee (IDMC) involvement?

Yes

Number of subjects enrolled per country

Country: Number of subjects enrolled

United States: 349

Worldwide total number of subjects

349

EEA total number of subjects

Number of subjects enrolled per age group

In utero

Preterm newborn - gestational age < 37 wk

Newborns (0-27 days)

Infants and toddlers (28 days-23 months)

Children (2-11 years)

255

Adolescents (12-17 years)

Adults (18-64 years)

From 65 to 84 years

85 years and over

Subject disposition

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Recruitment details

Screening details

This study consisted of 2 parts (Parts A and B). Part A consisted of 2 cohorts. For Part B, all Cohort 1 participants who were enrolled and dosed in Part A, were offered to re-enroll into the safety follow-up study. Participants who were in Part B were not administered any study drug.

Period 1 title

Part A

Is this the baseline period?

Yes

Allocation method

Randomised - controlled

Blinding used

Double blind

Roles blinded

Subject, Investigator, Carer, Assessor

Blinding implementation details

The study was observer-blind.

Are arms mutually exclusive

Yes

Part A Cohort 1: Placebo

Arm description

Participants received a single intramuscular (IM) injection of placebo on Day 1.

Arm type

Placebo

Investigational medicinal product name

Placebo

Investigational medicinal product code

Other name

Pharmaceutical forms

Solution for injection

Routes of administration

Intramuscular use

Dosage and administration details

Placebo matched to mRNA-1345 was administered per schedule specified in the arm description.

Part A Cohort 1: mRNA-1345 Dose Level 1

Arm description

Participants received a single IM injection of mRNA-1345 at Dose Level 1 on Day 1.

Arm type

Experimental

Investigational medicinal product name

mRNA-1345

Investigational medicinal product code

Other name

Pharmaceutical forms

Solution for injection

Routes of administration

Intramuscular use

Dosage and administration details

mRNA-1345 was administered per schedule specified in the arm description.

Part A Cohort 1: mRNA-1345 Dose Level 2

Arm description

Participants received a single IM injection of mRNA-1345 at Dose Level 2 on Day 1.

Arm type

Experimental

Investigational medicinal product name

mRNA-1345

Investigational medicinal product code

Other name

Pharmaceutical forms

Solution for injection

Routes of administration

Intramuscular use

Dosage and administration details

mRNA-1345 was administered per schedule specified in the arm description.

Part A Cohort 1: mRNA-1345 Dose Level 3

Arm description

Participants received a single IM injection of mRNA-1345 at Dose Level 3 on Day 1.

Arm type

Experimental

Investigational medicinal product name

mRNA-1345

Investigational medicinal product code

Other name

Pharmaceutical forms

Solution for injection

Routes of administration

Intramuscular use

Dosage and administration details

mRNA-1345 was administered per schedule specified in the arm description.

Part A Cohort 2: mRNA-1345 Dose Level 2

Arm description

Participants received a single IM injection of mRNA-1345 at Dose Level 2 on Day 1.

Arm type

Experimental

Investigational medicinal product name

mRNA-1345

Investigational medicinal product code

Other name

Pharmaceutical forms

Solution for injection

Routes of administration

Intramuscular use

Dosage and administration details

mRNA-1345 was administered per schedule specified in the arm description.

Part A Cohort 2: mRNA-1345 Dose Level 3

Arm description

Participants received a single IM injection of mRNA-1345 at Dose Level 3 on Day 1.

Arm type

Experimental

Investigational medicinal product name

mRNA-1345

Investigational medicinal product code

Other name

Pharmaceutical forms

Solution for injection

Routes of administration

Intramuscular use

Dosage and administration details

mRNA-1345 was administered per schedule specified in the arm description.

Part A Cohort 2: mRNA-1345 Dose Level 4

Arm description

Participants received a single IM injection of mRNA-1345 at Dose Level 4 on Day 1.

Arm type

Experimental

Investigational medicinal product name

mRNA-1345

Investigational medicinal product code

Other name

Pharmaceutical forms

Solution for injection

Routes of administration

Intramuscular use

Dosage and administration details

mRNA-1345 was administered per schedule specified in the arm description.

Number of subjects in period 1	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4
Started	41	40	42	41	62	61	62
Received Study Drug Injection	41	39	41	41	61	61	62
Completed	35	36	37	40	60	59	59
Not completed	6	4	5	1	2	2	3
Other Than Specified	-	-	1	-	-	-	-
Withdrawal by Parent/Guardian	2	-	-	-	2	-	-
Lost to follow-up	4	3	4	1	-	2	3
Protocol deviation	-	1	-	-	-	-	-

Period 2 title

Part B

Is this the baseline period?

Allocation method

Randomised - controlled

Blinding used

Double blind

Roles blinded

Subject, Investigator, Carer, Assessor

Blinding implementation details

The study was observer-blind.

Are arms mutually exclusive

Yes

Part B Cohort 1: Received Placebo in Part A

Arm description

Participants who received placebo in Part A and decided to continue in Part B of the study were followed up for safety assessment (for up to 6 months). Participants did not receive any study drug in Part B.

Arm type

No intervention

Investigational medicinal product name

No investigational medicinal product assigned in this arm

Part B Cohort 1: Received mRNA-1345 Dose Level 1 in Part A

Arm description

Participants who received mRNA-1345 at Dose Level 1 in Part A and decided to continue in Part B of the study were followed up for safety assessment (for up to 6 months). Participants did not receive any study drug in Part B.

Arm type

No intervention

Investigational medicinal product name

No investigational medicinal product assigned in this arm

Part B Cohort 1: Received mRNA-1345 Dose Level 2 in Part A

Arm description

Participants who received mRNA-1345 at Dose Level 2 in Part A and decided to continue in Part B of the study were followed up for safety assessment (for up to 6 months). Participants did not receive any study drug in Part B.

Arm type

No intervention

Investigational medicinal product name

No investigational medicinal product assigned in this arm

Part B Cohort 1: Received mRNA-1345 Dose Level 3 in Part A

Arm description

Participants who received mRNA-1345 at Dose Level 3 in Part A and decided to continue in Part B of the study were followed up for safety assessment (for up to 6 months). Participants did not receive any study drug in Part B.

Arm type

No intervention

Investigational medicinal product name

No investigational medicinal product assigned in this arm

Number of subjects in period 2 ^[1]	Part B Cohort 1: Received Placebo in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 1 in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 2 in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 3 in Part A
Started	19	24	25	24
Completed	19	24	25	23
Not completed	0	0	0	1
Lost to follow-up	-	-	-	1

Notes
[1] - The number of subjects starting the period is not consistent with the number completing the preceding period. It is expected the number of subjects starting the subsequent period will be the same as the number completing the preceding period.
Justification: Not all participants who completed Part A were re-enrolled in Part B.

Baseline characteristics

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Reporting group title

Part A Cohort 1: Placebo

Reporting group description

Participants received a single intramuscular (IM) injection of placebo on Day 1.

Reporting group title

Part A Cohort 1: mRNA-1345 Dose Level 1

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 1 on Day 1.

Reporting group title

Part A Cohort 1: mRNA-1345 Dose Level 2

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 2 on Day 1.

Reporting group title

Part A Cohort 1: mRNA-1345 Dose Level 3

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 3 on Day 1.

Reporting group title

Part A Cohort 2: mRNA-1345 Dose Level 2

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 2 on Day 1.

Reporting group title

Part A Cohort 2: mRNA-1345 Dose Level 3

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 3 on Day 1.

Reporting group title

Part A Cohort 2: mRNA-1345 Dose Level 4

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 4 on Day 1.

Reporting group values	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4	Total
Number of subjects	41	40	42	41	62	61	62	349
Age Categorical
Units: Subjects
In utero	0	0	0	0	0	0	0	0
Preterm newborn infants (gestational age < 37 wks)	0	0	0	0	0	0	0	0
Newborns (0-27 days)	0	0	0	0	0	0	0	0
Infants and toddlers (28 days-23 months)	0	0	0	0	0	0	0	0
Children (2-11 years)	41	40	42	41	30	30	31	255
Adolescents (12-17 years)	0	0	0	0	32	31	31	94
Adults (18-64 years)	0	0	0	0	0	0	0	0
From 65-84 years	0	0	0	0	0	0	0	0
85 years and over	0	0	0	0	0	0	0	0
Gender Categorical
Units: Subjects
Female	20	22	17	26	33	23	35	176
Male	21	18	25	15	29	38	27	173
Race
Units: Subjects
White	25	26	32	30	38	27	31	209
Black or African American	14	11	6	8	20	31	28	118
Asian	1	1	1	2	1	0	1	7
Multiple	1	2	3	1	3	3	2	15
Ethnicity
Units: Subjects
Hispanic or Latino	14	11	14	19	14	17	15	104
Not Hispanic or Latino	27	29	28	22	48	44	47	245

End points

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Reporting group title

Part A Cohort 1: Placebo

Reporting group description

Participants received a single intramuscular (IM) injection of placebo on Day 1.

Reporting group title

Part A Cohort 1: mRNA-1345 Dose Level 1

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 1 on Day 1.

Reporting group title

Part A Cohort 1: mRNA-1345 Dose Level 2

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 2 on Day 1.

Reporting group title

Part A Cohort 1: mRNA-1345 Dose Level 3

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 3 on Day 1.

Reporting group title

Part A Cohort 2: mRNA-1345 Dose Level 2

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 2 on Day 1.

Reporting group title

Part A Cohort 2: mRNA-1345 Dose Level 3

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 3 on Day 1.

Reporting group title

Part A Cohort 2: mRNA-1345 Dose Level 4

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 4 on Day 1.

Reporting group title

Part B Cohort 1: Received Placebo in Part A

Reporting group description

Reporting group title

Part B Cohort 1: Received mRNA-1345 Dose Level 1 in Part A

Reporting group description

Reporting group title

Part B Cohort 1: Received mRNA-1345 Dose Level 2 in Part A

Reporting group description

Reporting group title

Part B Cohort 1: Received mRNA-1345 Dose Level 3 in Part A

Reporting group description

Primary: Part A (Cohorts 1 and 2): Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs)

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End point title

Part A (Cohorts 1 and 2): Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs) ^[1]

End point description

Solicited ARs were collected in an electronic diary (eDiary). Local ARs: injection site pain, erythema (redness), swelling/induration (hardness); and axillary (underarm) swelling or tenderness ipsilateral to the side of injection. Systemic ARs: fever, headache, fatigue, myalgia, arthralgia, nausea/vomiting, and chills. Note, not all solicited ARs were considered adverse events (AEs). Investigator reviewed whether the solicited AR was also to be recorded as an AE. A summary of serious AEs (SAEs) and nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section. Solicited Safety Set included all randomized participants who received the study intervention and who contributed any solicited AR data.

End point type

Primary

End point timeframe

Up to 7 days postinjection

Notes
[1] - No statistical analyses have been specified for this primary end point. It is expected there is at least one statistical analysis for each primary end point.
Justification: The endpoint is descriptive in nature.

End point values	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4
Number of subjects analysed	41	39	41	41	61	61	62
Units: participants	18	21	28	30	45	44	51

No statistical analyses for this end point

Primary: Part A (Cohorts 1 and 2): Number of Participants with Unsolicited Adverse Events (AEs)

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End point title

Part A (Cohorts 1 and 2): Number of Participants with Unsolicited Adverse Events (AEs) ^[2]

End point description

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 (hematology, clinical chemistry, or prothrombin time [PT]/partial thromboplastin time [PTT]) or other safety assessment (for example, electrocardiogram, radiological scan, vital sign measurement), including one that worsened from baseline and was considered clinically significant in the medical and scientific judgment of the Investigator was recorded as an AE. A summary of SAEs and all nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section. Part A Safety Set included all randomized participants who received the study intervention.

End point type

Primary

End point timeframe

Up to 28 days postinjection

Notes
[2] - No statistical analyses have been specified for this primary end point. It is expected there is at least one statistical analysis for each primary end point.
Justification: The endpoint is descriptive in nature.

End point values	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4
Number of subjects analysed	41	39	41	41	61	61	62
Units: participants	9	9	3	10	11	5	6

No statistical analyses for this end point

Primary: Part A (Cohorts 1 and 2): Number of Participants With Medically Attended AEs (MAAEs), Adverse Events of Special Interest (AESIs), Serious Adverse Events (SAEs), and AEs Leading to Study Discontinuation

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End point title

Part A (Cohorts 1 and 2): Number of Participants With Medically Attended AEs (MAAEs), Adverse Events of Special Interest (AESIs), Serious Adverse Events (SAEs), and AEs Leading to Study Discontinuation ^[3]

End point description

A MAAE was an AE that led to an unscheduled visit to a healthcare practitioner. An AESI was 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. An SAE was defined as any AE that resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in disability, was a congenital anomaly/birth defect, or was an important medical event. A summary of SAEs and all nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section. Part A Safety Set included all randomized participants who received the study intervention.

End point type

Primary

End point timeframe

Day 1 through end of Part A (Month 6)

Notes
[3] - No statistical analyses have been specified for this primary end point. It is expected there is at least one statistical analysis for each primary end point.
Justification: The endpoint is descriptive in nature.

End point values	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4
Number of subjects analysed	41	39	41	41	61	61	62
Units: participants
MAAEs	3	4	5	9	10	8	9
AESIs	0	0	0	0	0	0	0
SAEs	0	0	0	0	0	0	3
AEs Leading to Study Discontinuation	0	0	0	0	0	0	0

No statistical analyses for this end point

Primary: Part B (Cohort 1): Number of participants With RSV-RTD, Respiratory syncytial virus- Lower Respiratory Tract Disease (RSV-LRTD), Severe RSV-LRTD, Very Severe RSV-LRTD and RSV Hospitalization Classified by Clinical Assessment Team (CAT)

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End point title

Part B (Cohort 1): Number of participants With RSV-RTD, Respiratory syncytial virus- Lower Respiratory Tract Disease (RSV-LRTD), Severe RSV-LRTD, Very Severe RSV-LRTD and RSV Hospitalization Classified by Clinical Assessment Team (CAT) ^[4]

End point description

RSV-RTD: Runny nose or blocked nose or cough and confirmed RSV infection. RSV-LRTD: Cough or difficulty breathing (Based on Investigator’s observation; difficulty breathing included signs of wheezing, stridor, tachypnoea, chest in-drawing or subcostal or intercostal retractions) and peripheral oxygen saturation (SpO2) <95%, or respiratory rate (RR) increased and confirmed RSV infection. RSV Severe-LRTD: Meeting the definition of RSV-LRTD and SpO2 <93%, or lower chest wall in-drawing. RSV Very Severe LRTD: Meeting the definition of RSV-LRTD and SpO2 <90%, or failure to respond/unconscious. RSV Hospitalization: Confirmed RSV and hospitalized for acute medical condition. Part B Cohort 1 Safety Set included all participants in the Part A Cohort 1 Safety Set who re-enrolled in Part B of the study.

End point type

Primary

End point timeframe

Day 1 through end of Part B (Month 6)

Notes
[4] - No statistical analyses have been specified for this primary end point. It is expected there is at least one statistical analysis for each primary end point.
Justification: The endpoint is descriptive in nature.

End point values	Part B Cohort 1: Received Placebo in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 1 in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 2 in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 3 in Part A
Number of subjects analysed	19	24	25	24
Units: participants
RSV-RTD	0	2	1	2
RSV-LRTD	0	1	0	0
RSV Severe LRTD	0	0	0	0
RSV Very-Severe LRTD	0	0	0	0
RSV Hospitalization	0	0	0	0

No statistical analyses for this end point

Secondary: Part A (Cohort 1): Geometric Mean Titer (GMT) of Serum RSV Neutralizing Antibody

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End point title

Part A (Cohort 1): Geometric Mean Titer (GMT) of Serum RSV Neutralizing Antibody ^[5]

End point description

Antibody values reported as below 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. LLOQ was 13 international units (IU)/milliliter (mL) for RSV-A and 10 IU/mL for RSV-B. ULOQ was 259061 IU/mL for RSV-A and 112476 IU/mL for RSV-B. 95% confidence interval (CI) for geometric mean (GM) value was calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation. Per-Protocol (PP) Set included all randomized participants who received the study injection, complied with the immunogenicity testing schedule, had a Baseline and Day 29 assessment, and had no important protocol deviations that affected the immune response. ‘n’ = participants evaluable for specified categories.

End point type

Secondary

End point timeframe

Day 1, Day 29, and Month 6

Notes
[5] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3
Number of subjects analysed	39	38	41	39
Units: IU/mL
geometric mean (confidence interval 95%)
RSV-A: Day 1 (n=39,38,41,39)	742.79 (406.66 to 1356.75)	636.62 (335.51 to 1207.99)	925.12 (553.23 to 1546.99)	1100.06 (642.50 to 1883.48)
RSV-A: Day 29 (n=39,38,41,39)	622.62 (365.59 to 1060.36)	7548.68 (4715.49 to 12084.11)	5454.33 (3321.91 to 8955.59)	13963.62 (8733.17 to 22326.68)
RSV-A: Month 6 (n=33,34,35,38)	767.32 (521.91 to 1128.13)	1978.73 (1207.90 to 3241.47)	1975.68 (1339.27 to 2914.51)	4129.82 (2471.64 to 6900.43)
RSV-B: Day 1 (n=39,38,41,39)	343.19 (193.35 to 609.18)	333.68 (187.03 to 595.33)	478.93 (293.74 to 780.85)	442.16 (266.78 to 732.83)
RSV-B: Day 29 (n=37,38,41,39)	310.51 (190.05 to 507.33)	2439.14 (1542.12 to 3857.94)	2043.38 (1282.91 to 3254.64)	3913.01 (2665.38 to 5744.65)
RSV-B: Month 6 (n=33,34,35,38)	351.86 (259.00 to 478.01)	708.25 (448.51 to 1118.41)	746.17 (533.81 to 1043.00)	975.64 (654.64 to 1454.04)

No statistical analyses for this end point

Secondary: Part A (Cohort 1): Geometric Mean Concentration (GMC) of Serum RSV Prefusion F (Pre-F) Binding Antibody

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End point title

Part A (Cohort 1): Geometric Mean Concentration (GMC) of Serum RSV Prefusion F (Pre-F) Binding Antibody ^[6]

End point description

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values greater than ULOQ were replaced by the ULOQ. LLOQ was 35 arbitrary units (AU)/mL and ULOQ was 580553 AU/mL for RSV Pre-F immunoglobulin G (IgG) antibody. 95% CI for GM value was calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation. PP Set included all randomized participants who received the study injection, complied with the immunogenicity testing schedule, had a Baseline and Day 29 assessment, and had no important protocol deviations that affected the immune response. ‘n’ = participants evaluable for specified categories.

End point type

Secondary

End point timeframe

Day 1, Day 29, and Month 6

Notes
[6] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3
Number of subjects analysed	39	38	41	39
Units: AU/mL
geometric mean (confidence interval 95%)
Day 1 (n=38,38,41,39)	5666.73 (2740.28 to 11718.45)	4824.82 (2238.62 to 10398.78)	7759.79 (4418.08 to 13629.08)	9200.11 (5456.47 to 15512.24)
Day 29 (n=39,36,39,39)	5478.04 (2980.57 to 10068.20)	60354.43 (43293.29 to 84139.08)	52861.15 (36058.06 to 77494.50)	93443.87 (69910.72 to 124898.70)
Month 6 (n=33,32,35,38)	6021.94 (4130.25 to 8780.02)	13070.48 (8101.85 to 21086.21)	14422.57 (10902.68 to 19078.86)	20054.12 (13907.99 to 28916.31)

No statistical analyses for this end point

Secondary: Part A (Cohort 1): Geometric Mean Fold Rise (GMFR) of Postbaseline/Baseline Neutralizing Antibody Titers

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End point title

Part A (Cohort 1): Geometric Mean Fold Rise (GMFR) of Postbaseline/Baseline Neutralizing Antibody Titers ^[7]

End point description

Antibody values reported as below lower LLOQ were replaced by 0.5*LLOQ. Values greater than the ULOQ were replaced by the ULOQ. LLOQ was 13 IU/mL for RSV-A and 10 IU/mL for RSV-B. ULOQ was 259061 IU/mL for RSV-A and 112476 IU/mL for RSV-B. 95% CI for GMFR (postinjection/baseline titers) was calculated based on the t-distribution of the differences in the log-transformed values between analysis timepoint and baseline, then back transformed to the original scale for presentation. PP Set included all randomized participants who received the study injection, complied with the immunogenicity testing schedule, had a Baseline and Day 29 assessment, and had no important protocol deviations that affected the immune response. ‘n’ = participants evaluable for specified categories.

End point type

Secondary

End point timeframe

Day 29 and Month 6

Notes
[7] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3
Number of subjects analysed	39	38	41	39
Units: ratio
geometric mean (confidence interval 95%)
RSV-A: Day 29 (n=39,38,41,39)	0.84 (0.68 to 1.04)	11.86 (7.23 to 19.43)	5.90 (3.55 to 9.79)	12.69 (7.74 to 20.82)
RSV-A: Month 6 (n=33,34,35,38)	0.90 (0.57 to 1.40)	3.66 (2.41 to 5.56)	1.70 (0.95 to 3.05)	3.78 (2.33 to 6.13)
RSV-B: Day 29 (n=37,38,41,39)	0.81 (0.66 to 0.99)	7.31 (4.82 to 11.08)	4.27 (2.74 to 6.64)	8.85 (5.59 to 14.02)
RSV-B: Month 6 (n=33,34,35,38)	0.99 (0.65 to 1.53)	2.46 (1.72 to 3.52)	1.23 (0.74 to 2.04)	2.12 (1.30 to 3.45)

No statistical analyses for this end point

Secondary: Part A (Cohort 1): GMFR of Postbaseline/Baseline Binding Antibody Concentrations

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End point title

Part A (Cohort 1): GMFR of Postbaseline/Baseline Binding Antibody Concentrations ^[8]

End point description

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values greater than ULOQ were replaced by the ULOQ. LLOQ was 35 AU/mL and ULOQ was 580553 AU/mL for RSV Pre-F IgG antibody. 95% CI for GMFR (postinjection/baseline titers) was calculated based on the t-distribution of the differences in the log-transformed values between analysis timepoint and baseline, then back transformed to the original scale for presentation. PP Set included all randomized participants who received the study injection, complied with the immunogenicity testing schedule, had a Baseline and Day 29 assessment, and had no important protocol deviations that affected the immune response. 'Overall number of participants analyzed' = participants evaluable for this endpoint. ‘n’ = participants evaluable for specified categories.

End point type

Secondary

End point timeframe

Day 29 and Month 6

Notes
[8] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3
Number of subjects analysed	38	36	39	39
Units: ratio
geometric mean (confidence interval 95%)
Day 29 (n=38,36,39,39)	0.94 (0.76 to 1.17)	13.43 (6.78 to 26.58)	6.63 (4.18 to 10.52)	10.16 (6.53 to 15.79)
Month 6 (n=32,32,35,38)	0.81 (0.48 to 1.37)	2.86 (1.68 to 4.87)	1.28 (0.81 to 2.05)	2.16 (1.41 to 3.33)

No statistical analyses for this end point

Secondary: Part A (Cohort 1): Percentage of Participants With Seroresponse in RSV Neutralizing Antibody

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End point title

Part A (Cohort 1): Percentage of Participants With Seroresponse in RSV Neutralizing Antibody ^[9]

End point description

Seroresponse was defined as a change from below the LLOQ to equal or above 4 * LLOQ, or at least a 4-fold increase if baseline was equal to or above the LLOQ. PP Set included all randomized participants who received the study injection, complied with the immunogenicity testing schedule, had a Baseline and Day 29 assessment, and had no important protocol deviations that affected the immune response. ‘n’ = participants evaluable for specified categories.

End point type

Secondary

End point timeframe

Baseline to Day 29 and Month 6

Notes
[9] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3
Number of subjects analysed	39	38	41	39
Units: percentage of participants
number (confidence interval 95%)
RSV-A: Day 29 (n=39,38,41,39)	2.6 (0.1 to 13.5)	78.9 (62.7 to 90.4)	46.3 (30.7 to 62.6)	79.5 (63.5 to 90.7)
RSV-A: Month 6 (n=33,34,35,38)	9.1 (1.9 to 24.3)	50.0 (32.4 to 67.6)	28.6 (14.6 to 46.3)	52.6 (35.8 to 69.0)
RSV-B: Day 29 (n=37,38,41,39)	0 (0.0 to 9.5)	63.2 (46.0 to 78.2)	48.8 (32.9 to 64.9)	71.8 (55.1 to 85.0)
RSV-B: Month 6 (n=33,34,35,38)	9.1 (1.9 to 24.3)	26.5 (12.9 to 44.4)	22.9 (10.4 to 40.1)	39.5 (24.0 to 56.6)

No statistical analyses for this end point

Secondary: Part A (Cohort 1): Percentage of Participants With Seroresponse in RSV Pre-F Binding Antibody

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End point title

Part A (Cohort 1): Percentage of Participants With Seroresponse in RSV Pre-F Binding Antibody ^[10]

End point description

Seroresponse was defined as a change from below the LLOQ to equal or above 4 * LLOQ, or at least a 4-fold increase if baseline was equal to or above the LLOQ. PP Set included all randomized participants who received the study injection, complied with the immunogenicity testing schedule, had a Baseline and Day 29 assessment, and had no important protocol deviations that affected the immune response. 'Overall number of participants analyzed' = participants evaluable for this endpoint. ‘n’ = participants evaluable for specified categories.

End point type

Secondary

End point timeframe

Baseline to Day 29 and Month 6

Notes
[10] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 1: Placebo	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3
Number of subjects analysed	38	36	39	39
Units: percentage of participants
number (confidence interval 95%)
Day 29 (n=38,36,39,39)	2.6 (0.1 to 13.8)	75.0 (57.8 to 87.9)	53.8 (37.2 to 69.9)	74.4 (57.9 to 87.0)
Month 6 (n=32,32,35,38)	6.3 (0.8 to 20.8)	21.9 (9.3 to 40.0)	17.1 (6.6 to 33.6)	36.8 (21.8 to 54.0)

No statistical analyses for this end point

Secondary: Part A (Cohort 2): GMT of Serum RSV Neutralizing Antibody

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End point title

Part A (Cohort 2): GMT of Serum RSV Neutralizing Antibody ^[11]

End point description

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values greater than the ULOQ were replaced by the ULOQ. LLOQ was 13 IU/mL for RSV-A and 15 IU/mL for RSV-B. ULOQ was 259061 IU/mL for RSV-A and 162163 IU/mL for RSV-B. 95% CI for GM value was calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation. PP Set included all randomized participants who received the study injection, complied with the immunogenicity testing schedule, had a Baseline and Day 29 assessment, and had no important protocol deviations that affected the immune response.

End point type

Secondary

End point timeframe

Day 1 and Day 29

Notes
[11] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4
Number of subjects analysed	59	58	60
Units: IU/mL
geometric mean (confidence interval 95%)
RSV-A: Day 1	1260.25 (943.55 to 1683.25)	1027.77 (749.05 to 1410.18)	1230.06 (946.64 to 1598.32)
RSV-A: Day 29	10168.70 (7560.52 to 13676.63)	9011.13 (6239.70 to 13013.52)	19541.50 (15311.61 to 24939.91)
RSV-B: Day 1	669.76 (506.07 to 886.40)	617.58 (449.58 to 848.35)	581.70 (463.11 to 730.66)
RSV-B: Day 29	3105.78 (2498.97 to 3859.94)	3523.27 (2598.78 to 4776.66)	4782.51 (4006.02 to 5709.50)

No statistical analyses for this end point

Secondary: Part A (Cohort 2): GMC of Serum RSV Pre-F Binding Antibody

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End point title

Part A (Cohort 2): GMC of Serum RSV Pre-F Binding Antibody ^[12]

End point description

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values greater than ULOQ were replaced by the ULOQ. LLOQ was 35 AU/mL and ULOQ was 580553 AU/mL for RSV Pre-F IgG antibody. 95% CI for GM value was calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation. PP Set included all randomized participants who received the study injection, complied with the immunogenicity testing schedule, had a Baseline and Day 29 assessment, and had no important protocol deviations that affected the immune response.

End point type

Secondary

End point timeframe

Day 1 and Day 29

Notes
[12] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4
Number of subjects analysed	59	58	60
Units: AU/mL
geometric mean (confidence interval 95%)
Day 1	11060.58 (8799.38 to 13902.85)	9556.54 (7002.35 to 13042.41)	11882.31 (10029.95 to 14076.78)
Day 29	67394.60 (54544.98 to 83271.33)	69494.70 (55349.62 to 87254.68)	109004.49 (94312.25 to 125985.52)

No statistical analyses for this end point

Secondary: Part A (Cohort 2): GMFR of Postbaseline/Baseline Neutralizing Antibody Titers

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End point title

Part A (Cohort 2): GMFR of Postbaseline/Baseline Neutralizing Antibody Titers ^[13]

End point description

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values greater than the ULOQ were replaced by the ULOQ. LLOQ was 13 IU/mL for RSV-A and 15 IU/mL for RSV-B. ULOQ was 259061 IU/mL for RSV-A and 162163 IU/mL for RSV-B. 95% CI for GMFR (postinjection/baseline titers) was calculated based on the t-distribution of the differences in the log-transformed values between analysis timepoint and baseline, then back transformed to the original scale for presentation. PP Set included all randomized participants who received the study injection, complied with the immunogenicity testing schedule, had a Baseline and Day 29 assessment, and had no important protocol deviations that affected the immune response.

End point type

Secondary

End point timeframe

Day 29

Notes
[13] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4
Number of subjects analysed	59	58	60
Units: ratio
geometric mean (confidence interval 95%)
RSV-A	8.07 (6.17 to 10.55)	8.77 (6.26 to 12.28)	15.89 (11.92 to 21.18)
RSV-B	4.64 (3.61 to 5.95)	5.71 (4.21 to 7.72)	8.22 (6.53 to 10.35)

No statistical analyses for this end point

Secondary: Part A (Cohort 2): GMFR of Postbaseline/Baseline Binding Antibody Concentrations

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End point title

Part A (Cohort 2): GMFR of Postbaseline/Baseline Binding Antibody Concentrations ^[14]

End point description

End point type

Secondary

End point timeframe

Day 29

Notes
[14] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4
Number of subjects analysed	59	58	60
Units: ratio
geometric mean (confidence interval 95%)	6.09 (4.77 to 7.78)	7.27 (5.43 to 9.73)	9.17 (7.65 to 10.99)

No statistical analyses for this end point

Secondary: Part A (Cohort 2): Percentage of Participants With Seroresponse in RSV Neutralizing Antibody

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End point title

Part A (Cohort 2): Percentage of Participants With Seroresponse in RSV Neutralizing Antibody ^[15]

End point description

End point type

Secondary

End point timeframe

Baseline to Day 29

Notes
[15] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4
Number of subjects analysed	59	58	60
Units: percentage of participants
number (confidence interval 95%)
RSV-A	76.3 (63.4 to 86.4)	75.9 (62.8 to 86.1)	86.7 (75.4 to 94.1)
RSV-B	54.2 (40.8 to 67.3)	60.3 (46.6 to 73.0)	71.7 (58.6 to 82.5)

No statistical analyses for this end point

Secondary: Part A (Cohort 2): Percentage of Participants With Seroresponse in RSV Pre-F Binding Antibody

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End point title

Part A (Cohort 2): Percentage of Participants With Seroresponse in RSV Pre-F Binding Antibody ^[16]

End point description

End point type

Secondary

End point timeframe

Baseline to Day 29

Notes
[16] - The end point is not reporting statistics for all the arms in the baseline period. It is expected all the baseline period arms will be reported on when providing values for an end point on the baseline period.
Justification: The endpoint is reporting statistics for the specified arms only.

End point values	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4
Number of subjects analysed	59	58	60
Units: percentage of participants
number (confidence interval 95%)	69.5 (56.1 to 80.8)	74.1 (61.0 to 84.7)	88.3 (77.4 to 95.2)

No statistical analyses for this end point

Secondary: Part B (Cohort 1): Number of Participants With AESIs and SAEs

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End point title

Part B (Cohort 1): Number of Participants With AESIs and SAEs

End point description

An AESI was 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. An SAE was defined as any AE that resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in disability, was a congenital anomaly/birth defect, or was an important medical event. A summary of SAEs and all nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section. Part B Cohort 1 Safety Set included all participants in the Part A Cohort 1 Safety Set who re-enrolled in Part B of the study.

End point type

Secondary

End point timeframe

Day 1 through Part B EOS (Month 6)

End point values	Part B Cohort 1: Received Placebo in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 1 in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 2 in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 3 in Part A
Number of subjects analysed	19	24	25	24
Units: participants
AESIs	0	1	0	0
SAEs	0	0	1	0

No statistical analyses for this end point

Adverse events

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Timeframe for reporting adverse events

All-cause mortality, SAEs, AESIs, MAAEs, and AEs leading to study discontinuation: up to Month 6 (Parts A & B). Other (non-serious) AEs: up to 28 days after study injection, unless they met criteria for AESIs, MAAEs, or AEs led to study discontinuation.

Adverse event reporting additional description

Part A Safety Set included all randomized participants who received the study intervention. Part B Cohort 1 Safety Set included all participants in the Part A Cohort 1 Safety Set who re-enrolled in Part B of the study.

Assessment type

Systematic

Dictionary name

MedDRA

Dictionary version

25.0

Reporting group title

Part A Cohort 1: mRNA-1345 Dose Level 1

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 1 on Day 1.

Reporting group title

Part A Cohort 1: Placebo

Reporting group description

Participants received a single IM injection of placebo on Day 1.

Reporting group title

Part A Cohort 2: mRNA-1345 Dose Level 2

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 2 on Day 1.

Reporting group title

Part A Cohort 1: mRNA-1345 Dose Level 3

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 3 on Day 1.

Reporting group title

Part A Cohort 1: mRNA-1345 Dose Level 2

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 2 on Day 1.

Reporting group title

Part A Cohort 2: mRNA-1345 Dose Level 3

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 3 on Day 1.

Reporting group title

Part A Cohort 2: mRNA-1345 Dose Level 4

Reporting group description

Participants received a single IM injection of mRNA-1345 at Dose Level 4 on Day 1.

Reporting group title

Part B Cohort 1: Received Placebo in Part A

Reporting group description

Participants who received placebo in Part A were followed up for safety assessment (for up to 6 months) in Part B. Participants did not receive any study drug in Part B.

Reporting group title

Part B Cohort 1: Received mRNA-1345 Dose Level 1 in Part A

Reporting group description

Participants who received mRNA-1345 at Dose Level 1 in Part A were followed up for safety assessment (for up to 6 months) in Part B. Participants did not receive any study drug in Part B.

Reporting group title

Part B Cohort 1: Received mRNA-1345 Dose Level 2 in Part A

Reporting group description

Participants who received mRNA-1345 at Dose Level 2 in Part A were followed up for safety assessment (for up to 6 months) in Part B. Participants did not receive any study drug in Part B.

Reporting group title

Part B Cohort 1: Received mRNA-1345 Dose Level 3 in Part A

Reporting group description

Participants who received mRNA-1345 at Dose Level 3 in Part A were followed up for safety assessment (for up to 6 months) in Part B. Participants did not receive any study drug in Part B.

Serious adverse events	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: Placebo	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4	Part B Cohort 1: Received Placebo in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 1 in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 2 in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 3 in Part A
Total subjects affected by serious adverse events
subjects affected / exposed	0 / 39 (0.00%)	0 / 41 (0.00%)	0 / 61 (0.00%)	0 / 41 (0.00%)	0 / 41 (0.00%)	0 / 61 (0.00%)	3 / 62 (4.84%)	0 / 19 (0.00%)	0 / 24 (0.00%)	1 / 25 (4.00%)	0 / 24 (0.00%)
number of deaths (all causes)	0	0	0	0	0	0	0	0	0	0	0
number of deaths resulting from adverse events
Injury, poisoning and procedural complications
Post procedural haemorrhage
subjects affected / exposed	0 / 39 (0.00%)	0 / 41 (0.00%)	0 / 61 (0.00%)	0 / 41 (0.00%)	0 / 41 (0.00%)	0 / 61 (0.00%)	1 / 62 (1.61%)	0 / 19 (0.00%)	0 / 24 (0.00%)	0 / 25 (0.00%)	0 / 24 (0.00%)
occurrences causally related to treatment / all	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 1	0 / 0	0 / 0	0 / 0	0 / 0
deaths causally related to treatment / all	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0
Respiratory, thoracic and mediastinal disorders
Asthma
Additional description: Both participants had a prior history of asthma.
subjects affected / exposed	0 / 39 (0.00%)	0 / 41 (0.00%)	0 / 61 (0.00%)	0 / 41 (0.00%)	0 / 41 (0.00%)	0 / 61 (0.00%)	2 / 62 (3.23%)	0 / 19 (0.00%)	0 / 24 (0.00%)	0 / 25 (0.00%)	0 / 24 (0.00%)
occurrences causally related to treatment / all	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 2	0 / 0	0 / 0	0 / 0	0 / 0
deaths causally related to treatment / all	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0
Infections and infestations
Influenza
subjects affected / exposed	0 / 39 (0.00%)	0 / 41 (0.00%)	0 / 61 (0.00%)	0 / 41 (0.00%)	0 / 41 (0.00%)	0 / 61 (0.00%)	0 / 62 (0.00%)	0 / 19 (0.00%)	0 / 24 (0.00%)	1 / 25 (4.00%)	0 / 24 (0.00%)
occurrences causally related to treatment / all	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 1	0 / 0
deaths causally related to treatment / all	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0

Frequency threshold for reporting non-serious adverse events: 5%

Non-serious adverse events	Part A Cohort 1: mRNA-1345 Dose Level 1	Part A Cohort 1: Placebo	Part A Cohort 2: mRNA-1345 Dose Level 2	Part A Cohort 1: mRNA-1345 Dose Level 3	Part A Cohort 1: mRNA-1345 Dose Level 2	Part A Cohort 2: mRNA-1345 Dose Level 3	Part A Cohort 2: mRNA-1345 Dose Level 4	Part B Cohort 1: Received Placebo in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 1 in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 2 in Part A	Part B Cohort 1: Received mRNA-1345 Dose Level 3 in Part A
Total subjects affected by non serious adverse events
subjects affected / exposed	3 / 39 (7.69%)	1 / 41 (2.44%)	5 / 61 (8.20%)	7 / 41 (17.07%)	1 / 41 (2.44%)	0 / 61 (0.00%)	0 / 62 (0.00%)	0 / 19 (0.00%)	0 / 24 (0.00%)	0 / 25 (0.00%)	0 / 24 (0.00%)
Infections and infestations
Gastroenteritis viral
subjects affected / exposed	2 / 39 (5.13%)	0 / 41 (0.00%)	1 / 61 (1.64%)	0 / 41 (0.00%)	0 / 41 (0.00%)	0 / 61 (0.00%)	0 / 62 (0.00%)	0 / 19 (0.00%)	0 / 24 (0.00%)	0 / 25 (0.00%)	0 / 24 (0.00%)
occurrences all number	2	0	1	0	0	0	0	0	0	0	0
Pharyngitis streptococcal
subjects affected / exposed	0 / 39 (0.00%)	0 / 41 (0.00%)	1 / 61 (1.64%)	3 / 41 (7.32%)	1 / 41 (2.44%)	0 / 61 (0.00%)	0 / 62 (0.00%)	0 / 19 (0.00%)	0 / 24 (0.00%)	0 / 25 (0.00%)	0 / 24 (0.00%)
occurrences all number	0	0	1	5	1	0	0	0	0	0	0
Upper respiratory tract infection
subjects affected / exposed	1 / 39 (2.56%)	1 / 41 (2.44%)	3 / 61 (4.92%)	4 / 41 (9.76%)	0 / 41 (0.00%)	0 / 61 (0.00%)	0 / 62 (0.00%)	0 / 19 (0.00%)	0 / 24 (0.00%)	0 / 25 (0.00%)	0 / 24 (0.00%)
occurrences all number	1	1	3	4	0	0	0	0	0	0	0

More information

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Were there any global substantial amendments to the protocol? Yes

18 Jun 2024

Amendment included following changes: Cohort 3 was added to test a single dose of mRNA-1345 Dose Level 4 in participants aged 2 to <5 years of age for further dose ranging.

02 Oct 2024

Amendment included following changes: Cohort 3 was removed from Part A and Cohort 1 Part B was added to include safety follow-up and RSV surveillance during the next RSV season for participants 2 to <5 years of age who were previously enrolled and received a study injection in Cohort 1 of Part A.

Were there any global interruptions to the trial? Yes

Date	Interruption	Restart date
07 Aug 2024	A United States Food and Drug Administration (US FDA)-requested clinical hold applied for participants RSV-seronegative aged 2 to <5 years. Enrollment had been completed prior to the hold effective date	-

Limitations of the trial such as small numbers of subjects analysed or technical problems leading to unreliable data.

None reported

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Clinical trials

Clinical Trial Results: A Phase 2, Randomized, Observer-blind Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of mRNA-1345, an mRNA Vaccine Targeting Respiratory Syncytial Virus, in Children 2 to <18 Years of Age at High Risk of Respiratory Syncytial Virus Disease

Trial information

Trial information

Subject disposition

Subject disposition

Baseline characteristics

Baseline characteristics

End points

End points

Primary: Part A (Cohorts 1 and 2): Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs)

Primary: Part A (Cohorts 1 and 2): Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs)

Primary: Part A (Cohorts 1 and 2): Number of Participants with Unsolicited Adverse Events (AEs)

Primary: Part A (Cohorts 1 and 2): Number of Participants with Unsolicited Adverse Events (AEs)

Primary: Part A (Cohorts 1 and 2): Number of Participants With Medically Attended AEs (MAAEs), Adverse Events of Special Interest (AESIs), Serious Adverse Events (SAEs), and AEs Leading to Study Discontinuation

Primary: Part A (Cohorts 1 and 2): Number of Participants With Medically Attended AEs (MAAEs), Adverse Events of Special Interest (AESIs), Serious Adverse Events (SAEs), and AEs Leading to Study Discontinuation

Primary: Part B (Cohort 1): Number of participants With RSV-RTD, Respiratory syncytial virus- Lower Respiratory Tract Disease (RSV-LRTD), Severe RSV-LRTD, Very Severe RSV-LRTD and RSV Hospitalization Classified by Clinical Assessment Team (CAT)

Primary: Part B (Cohort 1): Number of participants With RSV-RTD, Respiratory syncytial virus- Lower Respiratory Tract Disease (RSV-LRTD), Severe RSV-LRTD, Very Severe RSV-LRTD and RSV Hospitalization Classified by Clinical Assessment Team (CAT)

Secondary: Part A (Cohort 1): Geometric Mean Titer (GMT) of Serum RSV Neutralizing Antibody

Secondary: Part A (Cohort 1): Geometric Mean Titer (GMT) of Serum RSV Neutralizing Antibody

Secondary: Part A (Cohort 1): Geometric Mean Concentration (GMC) of Serum RSV Prefusion F (Pre-F) Binding Antibody

Secondary: Part A (Cohort 1): Geometric Mean Concentration (GMC) of Serum RSV Prefusion F (Pre-F) Binding Antibody

Secondary: Part A (Cohort 1): Geometric Mean Fold Rise (GMFR) of Postbaseline/Baseline Neutralizing Antibody Titers

Secondary: Part A (Cohort 1): Geometric Mean Fold Rise (GMFR) of Postbaseline/Baseline Neutralizing Antibody Titers

Secondary: Part A (Cohort 1): GMFR of Postbaseline/Baseline Binding Antibody Concentrations

Secondary: Part A (Cohort 1): GMFR of Postbaseline/Baseline Binding Antibody Concentrations

Secondary: Part A (Cohort 1): Percentage of Participants With Seroresponse in RSV Neutralizing Antibody

Secondary: Part A (Cohort 1): Percentage of Participants With Seroresponse in RSV Neutralizing Antibody

Secondary: Part A (Cohort 1): Percentage of Participants With Seroresponse in RSV Pre-F Binding Antibody

Secondary: Part A (Cohort 1): Percentage of Participants With Seroresponse in RSV Pre-F Binding Antibody

Secondary: Part A (Cohort 2): GMT of Serum RSV Neutralizing Antibody

Secondary: Part A (Cohort 2): GMT of Serum RSV Neutralizing Antibody

Secondary: Part A (Cohort 2): GMC of Serum RSV Pre-F Binding Antibody

Secondary: Part A (Cohort 2): GMC of Serum RSV Pre-F Binding Antibody

Secondary: Part A (Cohort 2): GMFR of Postbaseline/Baseline Neutralizing Antibody Titers

Secondary: Part A (Cohort 2): GMFR of Postbaseline/Baseline Neutralizing Antibody Titers

Secondary: Part A (Cohort 2): GMFR of Postbaseline/Baseline Binding Antibody Concentrations

Secondary: Part A (Cohort 2): GMFR of Postbaseline/Baseline Binding Antibody Concentrations

Secondary: Part A (Cohort 2): Percentage of Participants With Seroresponse in RSV Neutralizing Antibody

Secondary: Part A (Cohort 2): Percentage of Participants With Seroresponse in RSV Neutralizing Antibody

Secondary: Part A (Cohort 2): Percentage of Participants With Seroresponse in RSV Pre-F Binding Antibody

Secondary: Part A (Cohort 2): Percentage of Participants With Seroresponse in RSV Pre-F Binding Antibody

Secondary: Part B (Cohort 1): Number of Participants With AESIs and SAEs

Secondary: Part B (Cohort 1): Number of Participants With AESIs and SAEs

Adverse events

Adverse events

More information

Substantial protocol amendments (globally)

Interruptions (globally)

Limitations and caveats

More information

Clinical Trial Results:
A Phase 2, Randomized, Observer-blind Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of mRNA-1345, an mRNA Vaccine Targeting Respiratory Syncytial Virus, in Children 2 to <18 Years of Age at High Risk of Respiratory Syncytial Virus Disease