A Safety, Tolerability, and Immunogenicity Study of mRNA-1345 and mRNA-1365 in Participants Aged 5 Months to <24 Months

A Phase 1, Randomized, Observer-blind, Placebo-controlled, Age De-escalation Study of the Safety, Tolerability, and Immunogenicity of mRNA-1345 and mRNA-1365 in Participants Aged 5 Months to <24 Months

The purpose of this study is to assess the safety and immunogenicity of mRNA-1365, an mRNA vaccine targeting respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) and mRNA-1345, an mRNA vaccine targeting RSV, in participants aged 5 months to <24 months.

Study Overview

• Status: Active, not recruiting
• Conditions: Respiratory Syncytial Virus; Human Metapneumovirus
• Intervention / Treatment: Biological: mRNA-1345; Biological: mRNA-1365; Biological: Placebo; Drug: Nimenrix

• Study Type: Interventional
• Enrollment (Actual): 186
• Phase: Phase 1

Contacts and Locations

Study Locations

• Panama
  • Panama City, Panama, 0801
    • CEVAXIN Avenida Mexico
  • Panama City, Panama
    • CEVAXIN 24 de Diciembre
  • Chiriquí Province
    • David, Chiriquí Province, Panama, 0401
      • CEVAXIN David
  • Panamá Oeste Province
    • La Chorrera, Panamá Oeste Province, Panama
      • CEVAXIN Chorrera
• United Kingdom
  • Norwich, United Kingdom, NR4 7UY
    • Norfolk and Norwich University Hospitals
• United States
  • California
    • Los Angeles, California, United States, 90057
      • Matrix Clinical Research
  • District of Columbia
    • Washington D.C., District of Columbia, United States, 20016
      • Meridian Clinical Research
  • Illinois
    • Melrose Park, Illinois, United States, 60160
      • DM Clinical Research- River Forest
  • Louisiana
    • Lafayette, Louisiana, United States, 70508
      • MedPharmics - Platinum - PPDS
  • North Carolina
    • Durham, North Carolina, United States, 27703
      • Duke Vaccine and Trials Unit
  • Rhode Island
    • Providence, Rhode Island, United States, 02886
      • Velocity Clinical Research - Providence
  • South Carolina
    • North Charleston, South Carolina, United States, 29406-9170
      • Palmetto Pediatrics, PA
  • Tennessee
    • Nashville, Tennessee, United States, 37232
      • Vanderbilt Vaccine Research Program
  • Texas
    • Houston, Texas, United States, 77087
      • Pediatric Associates
    • Houston, Texas, United States, 77065
      • CyFair
    • Plano, Texas, United States, 75024
      • Village Pediatrics
    • Richmond, Texas, United States, 77469
      • Pediatric Center

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 5 months to 2 years (Child)
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• The participant is 8 months to <24 months (Part A), 5 months to <8 months (Part B), or 8 months to <12 months (Part C) of age at the time of randomization (Day 1/Baseline visit), who is in good general health, in the opinion of the Investigator, based on review of medical history and screening physical examination.
• In the Investigator's opinion, the parent(s)/ legally authorized representative (LAR)(s) understand and are willing and physically able to comply with protocol-mandated follow up, including all procedures, and provide written informed consent.
• The participant is growing normally for age in the opinion of the site clinician in the months prior to enrollment.
• The participant was born at full-term (≥37 weeks gestation) with a minimum birth weight of 2.5 kilograms (kg).
• For Part C Cohort 7: participant must have received nirsevimab ≥6 months prior to Day 1 Visit.
• For Part C Cohort 8: participant was eligible at any time since birth, according to national guidelines, to receive nirsevimab prior to Day 1 Visit but did not do so.

Exclusion Criteria:

• Has a known history of symptomatic RSV (Part A: within 3 months; Part B and Part C: since birth) or hMPV infection (Part A: within 3 months; Part B: since birth) prior to administration of the first dose of investigational product (IP) or has a known close contact with anyone with laboratory-confirmed RSV (Parts A, B, and C) or hMPV infection (Parts A or B) within 14 days prior to administration of the first dose of IP.
• Is acutely ill or febrile 24 hours prior to or at the screening visit. Fever is defined as a body temperature ≥38.0°Celsius/≥100.4°Fahrenheit. Participants who meet this criterion may have visits rescheduled within the relevant study visit windows.
• Has previously been administered an investigational or approved vaccine for prevention of RSV (Parts A, B, and C) or hMPV (Parts A and B) infection or if the participant's mother received an investigational or approved vaccine for the prevention of RSV (Parts A, B, and C) or hMPV (Parts A and B) infection during pregnancy.
• Has received investigational or approved agents for prophylaxis against RSV or hMPV (for example, monoclonal antibodies) or is intending to receive these during the course of the study. For Part C (Cohort 7 only), use of nirsevimab ≥6 months before Day 1 Visit is allowed.
• Has a known hypersensitivity to a component of the vaccine or its excipients. Hypersensitivity includes, but is not limited to, anaphylaxis or immediate allergic reaction of any severity to a previous dose of an mRNA vaccine or any of its components (including polyethylene glycol or immediate allergic reaction of any severity to polysorbate).
• Has a medical condition that, according to the Investigator's judgment, may pose additional risk as a result of participation, interfere with safety assessments, or interfere with interpretation of results.

Note: Other protocol-defined inclusion/exclusion criteria apply.

Inclusion Criteria:

• For Part B Extension: participants enrolled and dosed in Part B (Cohorts 3 to 6); either reached the end of study of the Main Study or were dosed and subsequently discontinued from the Main Study. This includes participants who were lost to follow-up, if they can be re-engaged.
• For Part B Extension: participant's parent(s)/LAR(s) has provided written informed consent for participation in Part B of the Main Study and the Part B Extension.

Exclusion Criteria:

• For Part B Extension, there are no specific exclusion criteria.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Triple

Number of Arms

15

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Part A: mRNA-1345, Dose 1 (Age Group: 8 to <24 months); Participants will receive mRNA-1345 vaccine by intramuscular (IM) injection on Days 1, 57 and 113.	Biological: mRNA-1345; Sterile liquid for injection
Experimental: Part A: mRNA-1365, Dose 1 (Age Group: 8 to <24 months); Participants will receive mRNA-1365 vaccine by IM injection on Days 1, 57 and 113.	Biological: mRNA-1365; Sterile liquid for injection
Placebo Comparator: Part A: Placebo (Age Group: 8 to <24 months); Participants will receive mRNA-1345/ mRNA-1365 vaccine matching placebo by IM injection on Days 1, 57 and 113. In countries where applicable, participants may receive Nimenrix instead of placebo on Day 113.	Biological: Placebo; 0.9% sodium chloride (normal saline) solution for injection; Drug: Nimenrix; Solution for injection
Experimental: Part B: mRNA-1345, Dose 2 (Age Group: 5 to <8 months); Participants will receive mRNA-1345 by IM injection on Days 1, 57 and 113.	Biological: mRNA-1345; Sterile liquid for injection
Experimental: Part B: mRNA-1365, Dose 2 (Age Group: 5 to <8 months); Participants will receive mRNA-1365 by IM injection on Days 1, 57 and 113.	Biological: mRNA-1365; Sterile liquid for injection
Experimental: Part B: mRNA-1345 Dose 1 (Age Group: 5 to <8 months); Participants will receive mRNA-1345 by IM injection on Days 1, 57 and 113.	Biological: mRNA-1345; Sterile liquid for injection
Experimental: Part B: mRNA-1365 Dose 1 (Age Group: 5 to <8 months); Participants will receive mRNA-1365 by IM injection on Days 1, 57 and 113.	Biological: mRNA-1365; Sterile liquid for injection
Placebo Comparator: Part B: Placebo (Age Group: 5 to <8 months); Participants will receive mRNA-1345/ mRNA-1365 vaccine matching placebo by IM injection on Days 1, 57 and 113. In countries where applicable, participants may receive Nimenrix instead of placebo on Day 113.	Biological: Placebo; 0.9% sodium chloride (normal saline) solution for injection; Drug: Nimenrix; Solution for injection
No Intervention: Part B Extension: mRNA-1345, Dose 2 (Age Group: 5 to <8 months); Participants will have the option to re-enrol in the Part B extension period.
No Intervention: Part B Extension: mRNA-1365, Dose 2 (Age Group: 5 to <8 months); Participants will have the option to re-enrol in the Part B extension period.
No Intervention: Part B Extension: mRNA-1345 Dose 1 (Age Group: 5 to <8 months); Participants will have the option to re-enrol in the Part B extension period.
No Intervention: Part B Extension: mRNA-1365 Dose 1 (Age Group: 5 to <8 months); Participants will have the option to re-enrol in the Part B extension period.
No Intervention: Part B Extension : Placebo (Age Group: 5 to <8 months); Participants will have the option to re-enrol in the Part B extension period.
Experimental: Part C: mRNA-1345 Dose 1 (Age Group 8 to <12 months exposed to nirsevimab); Participants who have been previously exposed to nirsevimab will receive mRNA 1345 by IM injection on Days 1, 57, and 113.	Biological: mRNA-1345; Sterile liquid for injection
Experimental: Part C: mRNA-1345 Dose 1 (Age Group 8 to <12 months not exposed to nirsevimab); Participants who have not been previously exposed to nirsevimab will receive mRNA 1345 by IM injection on Days 1, 57, and 113.	Biological: mRNA-1345; Sterile liquid for injection

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Main Study: Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs)	Up to Day 120 (7 days after each injection)
Main Study: Number of Participants with Unsolicited Adverse Events (AEs)	Up to Day 141 (28 days after each injection)
Main Study: Number of Participants with Medically-Attended Adverse Events (MAAEs)	Day 1 through Day 730
Main Study: Number of Participants with Adverse Event of Special Interests (AESIs), Serious Adverse Events (SAEs) and Adverse Events Leading to Discontinuation	Day 1 through Day 730
Part B Extension: Number of Participants with MAAEs, AESIs and SAEs	Day 1 of the Extension to end of study (EoS) (up to 3 years)
Part B Extension: Number of Participants with Lower Respiratory Tract Illness (LRTI), Severe LRTI, Very Severe LRTI, and Hospitalizations Associated with RSV or hMPV	Day 1 of the Extension to EoS (up to 3 years)

Secondary Outcome Measures

Outcome Measure	Time Frame
Main Study: Number of Participants with Respiratory tract Illness (RTI), LRTI, Severe LRTI, Very Severe LRTI, and Hospitalizations Associated with RSV or hMPV	Day 1 through Day 730
Main Study (Parts A and B): Geometric Mean Titer (GMT) of Serum RSV and hMPV Neutralizing Antibodies	Baseline up to Month 12
Main Study (Part C): GMT of Serum RSV Neutralizing Antibodies	Baseline up to Month 12
Main Study (Parts A and B): Geometric Mean Concentration (GMC) of Serum RSV F- and hMPV F-Binding Antibodies	Baseline up to Month 12
Main Study (Part C): GMC of Serum RSV F-Binding Antibodies	Baseline up to Month 12
Main Study: Geometric Mean Fold-Rise (GMFR) of Postbaseline/baseline Neutralizing Antibody Titers and Binding Antibody	Month 12
Main Study: Number of Participants with Vaccine-specific T-cell Responses Measured by Flow Cytometry	Baseline up to Month 12
Part B Extension: Geometric Mean Titer (GMT) of Serum RSV and hMPV Neutralizing Antibodies	Day 1 of the Extension up to EoS (up to 3 years)
Part B Extension: Geometric Mean Concentration (GMC) of Serum RSV F- and hMPV F-Binding Antibodies	Day 1 of the Extension up to EoS (up to 3 years)
Part B Extension: Geometric Mean Fold-Rise (GMFR) of Postbaseline/baseline Neutralizing Antibody Titers and Binding Antibody	Day 1 of the Extension up to EoS (up to 3 years)
Part B Extension: Number of Participants with Vaccine-specific T-cell Responses Measured by Flow Cytometry	Day 1 of the Extension up to EoS (up to 3 years)

Collaborators and Investigators

• Sponsor: ModernaTX, Inc.

Publications and helpful links

General Publications

• Amodio D, Angelidou A, Cotugno N, Sherman AC, Levy O, Palma P; IPVC 2023 Speakers' group. Biomarkers of vaccine safety and efficacy in vulnerable populations: Lessons from the fourth international precision vaccines conference. Vaccine. 2025 Jan 1;43(Pt 2):126477. doi: 10.1016/j.vaccine.2024.126477. Epub 2024 Nov 28.

Study record dates

Study Major Dates

• Study Start (Actual): February 15, 2023
• Primary Completion (Estimated): August 31, 2029
• Study Completion (Estimated): August 31, 2029

Study Registration Dates

• First Submitted: February 15, 2023
• First Submitted That Met QC Criteria: February 15, 2023
• First Posted (Actual): February 24, 2023

Study Record Updates

• Last Update Posted (Actual): June 26, 2026
• Last Update Submitted That Met QC Criteria: June 23, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: mRNA-1345; mRNA-1365; RSV vaccine; hMPV vaccine; RSV/hMPV vaccine
• Additional Relevant MeSH Terms: mRNA-1345 respiratory syncytial virus vaccine
• Other Study ID Numbers: mRNA-1365-P101; 2022-502022-41 (EudraCT Number); 2022-502022-41-00 (Other Identifier: EU CT Number)

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No