A Study of mRNA-1345 Vaccine Targeting Respiratory Syncytial Virus in Pregnant Women and in Infants Born to Vaccinated Mothers

February 3, 2026 updated by: ModernaTX, Inc.

A Phase 2, Randomized, Observer-Blind, Placebo-Controlled, Dose-Escalation Study to Evaluate the Reactogenicity, Safety, and Immunogenicity of mRNA-1345, an mRNA Vaccine Targeting Respiratory Syncytial Virus, in Pregnant Women, and Safety and Immunogenicity in Infants Born to Vaccinated Mothers

The purpose of the study is to evaluate the reactogenicity, safety, and immunogenicity of an investigational respiratory syncytial virus (RSV) vaccine, mRNA-1345, in pregnant women, and safety and immunogenicity in infants born to vaccinated mothers.

Study Overview

Status

Active, not recruiting

Conditions

Intervention / Treatment

Study Type

Interventional

Enrollment (Actual)

360

Phase

  • Phase 2

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Canada
      • Québec, Canada, G1V 4G2
        • Centre Hospitalier de l'Universite Laval
    • Nova Scotia
      • Halifax, Nova Scotia, Canada, B3H 1
        • Dalhousie University - 5820 University Ave
    • Ontario
      • Ottawa, Ontario, Canada, K1H 8L6
        • Ottawa Hospital
    • Quebec
      • Montreal, Quebec, Canada, H3T 1C5
        • Sainte Justine Hospital
  • Chile
      • Santiago, Chile, 8380453
        • Red Hospital Clinico de la Universidad de Chile
    • Región-MetropolitanadeSantiago
      • Las Condes, Región-MetropolitanadeSantiago, Chile, 7550000
        • Clinica Universidad de Los Andes
      • Recoleta, Región-MetropolitanadeSantiago, Chile, 8420000
        • Centro Internacional de Estudios Clínicos
  • Denmark
    • Capital
      • Hvidovre, Capital, Denmark, DK-2650
        • Hvidovre Hospital
    • Central Jutland
      • Aarhus, Central Jutland, Denmark, 8200
        • Aarhus Universitetshospital
      • Herning, Central Jutland, Denmark, 7400
        • Regionshospitalet Gødstrup
  • Japan
    • Kanagawa
      • Kamakura-Shi, Kanagawa, Japan, 247-8533
        • Shonan Kamakura General Hospital
      • Yokohama, Kanagawa, Japan, 234-0054
        • Saiseikai Yokohamashi Nanbu Hospital
    • Saitama
      • Saitama-Shi, Saitama, Japan, 336-0911
        • Saitama City Hospital
    • Tokyo
      • Shinjuku-Ku, Tokyo, Japan, 162-8655
        • Center Hospital of the National Center for Global Health and Medicine
  • Panama
      • Panama City, Panama
        • CEVAXIN 24 de Diciembre
      • Panama City, Panama
        • Centro De Vacunacion Internacional, S.A. (Cevaxin) Sede La Chorrera
      • Panama City, Panama
        • Centro De Vacunacion Internacional, S.A. (Cevaxin)
      • Pueblo Nuevo, Panama
        • Instituto de Investigaciones Científicas Y Servicios de Alta Tecnología Asociación de Interés Panama
    • Chiriquí Province
      • David, Chiriquí Province, Panama
        • Centro De Vacunacion Internacional, S.A. (Cevaxin) - David
  • South Africa
    • Free State
      • Bloemfontein, Free State, South Africa, 9300
        • Josha Research
      • Welkom, Free State, South Africa, 9459
        • Drs. YAK Vahed & Partners
    • Gauteng
      • Krugersdorp, Gauteng, South Africa, 1739
        • Ubuntu Clinical Research
      • Pretoria, Gauteng, South Africa, 0184
        • Bothe ke Bontle Health Services-316 Kuit st
      • Soshanguve, Gauteng, South Africa, 152
        • Setshaba Research Centre
      • Soweto, Gauteng, South Africa, 2013
        • WITS Clinical Research Site - PPDS
    • Mpumalanga
      • Middelburg, Mpumalanga, South Africa, 1050
        • Merclinico Middelburg
    • Western Cape
      • Cape Town, Western Cape, South Africa, 7505
        • FAM-CRU
  • United Kingdom
      • Glasgow, United Kingdom, G51 4TF
        • Glasgow Clinical Research Facility - PPDS
    • Dorset
      • Bournemouth, Dorset, United Kingdom, BH7 7DW
        • Royal Bournemouth Hospital
    • Hampshire
      • Southampton, Hampshire, United Kingdom
        • Southampton General Hospital
    • London, City of
      • London, London, City of, United Kingdom, E1 1FR
        • The Royal London Hospital
    • Middlesex
      • London, Middlesex, United Kingdom, NW3 2QG
        • The Royal Free Hospital
    • South Glamorgan
      • Cardiff, South Glamorgan, United Kingdom, CF14 4XN
        • Cardiff & Vale University Health Board-PPDS
    • Surrey
      • London, Surrey, United Kingdom, SW17 0QT
        • St George's Hospital
  • United States
    • Alabama
      • Dothan, Alabama, United States, 36305-7376
        • SEC Clinical Research LLC - Dothan 2 - ClinEdge - PPDS
    • Arizona
      • Phoenix, Arizona, United States, 85031-3878
        • Abby's Research Institute
      • Tucson, Arizona, United States, 85712
        • Watching Over Mothers & Babies
    • Arkansas
      • Little Rock, Arkansas, United States, 72212-4169
        • Applied Research Center of Arkansas - ClinEdge - PPDS
    • California
      • Gardena, California, United States, 90247-4956
        • Matrix Clinical Research - Gardena
      • Huntington Park, California, United States, 90255-2913
        • Matrix Clinical Research - Huntington Park
      • Los Angeles, California, United States, 90057-4103
        • Matrix Clinical Research, Inc - Corporate Office
    • Idaho
      • Idaho Falls, Idaho, United States, 83404-5305
        • Clinical Research Prime - ClinEdge - PPDS
      • Pocatello, Idaho, United States, 83201
        • Bingham Memorial Hospital
      • Rexburg, Idaho, United States, 83440-5390
        • Clinical Research Prime - ClinEdge - Rexburg - PPDS
    • Louisiana
      • Covington, Louisiana, United States, 70433-7237
        • Velocity Clinical Research - Covington - PPDS
    • Michigan
      • Saginaw, Michigan, United States, 48604-9533
        • Saginaw Valley Medical Research Group LLC
    • Montana
      • Great Falls, Montana, United States, 59405-5316
        • Boeson Research GTF - Great Falls - ERN - PPDS
      • Kalispell, Montana, United States, 59901-2158
        • Boeson Research KAL - Kalispell - ERN - PPDS
      • Missoula, Montana, United States, 59804-7401
        • Boeson Research MSO - Missoula - ERN - PPDS
    • Nebraska
      • Grand Island, Nebraska, United States, 68803-4327
        • Velocity Clinical Research (Grand Island - Nebraska) - PPDS
      • Hastings, Nebraska, United States, 68901-2615
        • Velocity Clinical Research (Hastings - Nebraska) - PPDS
      • Norfolk, Nebraska, United States, 68701-7701
        • Velocity Clinical Research (Norfolk - Nebraska) - PPDS
    • Texas
      • Houston, Texas, United States, 77081
        • DM Clinical Research - Bellaire - ERN - PPDS
      • League City, Texas, United States, 77573-2681
        • Maximos Ob/Gyn
      • Mesquite, Texas, United States, 75149
        • SMS Clinical Research
    • Utah
      • Salt Lake City, Utah, United States, 84132-0001
        • Maternal Fetal Diagnostics Center

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Child
  • Adult

Accepts Healthy Volunteers

Yes

Description

Key Inclusion Criteria:

Maternal Participants

  • Are adults ≥18 years to <40 years of age inclusive, at the time of signing the informed consent.
  • Will be 28 to 36 weeks pregnant at the time of vaccination (confirmed by an obstetric ultrasound report).
  • Intend to deliver at a maternity unit where study procedures can be performed.
  • Are willing and able to attend all study visits, to undergo all study procedures/or have their infant undergo all study procedures, and to comply with study requirements, including a means of communication (for example, phone, text message or email) with study site staff.
  • Have engaged with local antenatal care and will continue to do so through the remainder of their pregnancy.
  • Have had an antenatal obstetric ultrasound at ≥18 weeks of pregnancy or be willing to have an antenatal obstetric ultrasound at Screening if not already conducted.

Specific inclusion criteria for Japanese pregnant women:

  • Japanese participants are defined as individuals born in Japan, with both parents and 4 grandparents who were born in Japan.

Infant Participants

  • Have consent from infant participant's parent(s)/legally authorized representative (LAR) if required by local regulations.

Key Exclusion Criteria:

Maternal Participants

  • Acutely ill or febrile (temperature ≥38.0 degrees Celsius [℃]/100.4 degrees Fahrenheit [°F]) within 72 hours prior to or at the Screening Visit or Day 1.
  • Reported history of anaphylaxis or severe hypersensitivity reaction after receipt of any mRNA vaccine or therapeutic or any components of an mRNA-1345 vaccine.
  • Any medical, psychiatric, or occupational condition, including reported history of drug or alcohol abuse, that, in the opinion of the Investigator, might pose additional risk due to participation in the study or could interfere with the interpretation of study results.
  • Have conditions in the current pregnancy or in previous pregnancies that may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to study procedures.
  • Received or plans to receive any mRNA vaccine or COVID-19 vaccine within 4 weeks before or after Day 1 and/or any other nonstudy vaccine within 2 weeks before or after Day 1.
  • Previous vaccination with any licensed or investigational RSV vaccine or planned receipt during study participation.
  • Intend for their infant to receive RSV monoclonal antibodies after delivery.

Infant Participants

  • Is a child who has been placed under the control or protection of an agency, organization, institution, or entity by the courts, the government, or a government body acting in accordance with powers conferred on them by laws and regulation (for example, foster care). This does not include a child who is adopted or has an appointed LAR.

Other inclusion and exclusion criteria may apply.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Prevention
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Quadruple

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: mRNA-1345 Dose A
Participants will be vaccinated in the period from 28 weeks to 36 weeks of gestation with a single intramuscular (IM) injection of mRNA-1345 Dose A.
Biological: mRNA-1345
Sterile liquid for injection
Experimental: mRNA-1345 Dose B
Participants will be vaccinated in the period from 28 weeks to 36 weeks of gestation with a single IM injection of mRNA-1345 Dose B.
Biological: mRNA-1345
Sterile liquid for injection
Experimental: mRNA-1345 Dose C
Participants will be vaccinated in the period from 28 weeks to 36 weeks of gestation with a single IM injection of mRNA-1345 Dose C.
Biological: mRNA-1345
Sterile liquid for injection
Placebo Comparator: Placebo
Participants will receive single IM injection of mRNA-1345 vaccine matching placebo in the period from 28 weeks to 36 weeks of gestation.
Biological: Placebo
0.9% sodium chloride (normal saline) injection

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Number of Maternal Participants with Solicited Local and Systemic Adverse Reactions (ARs)
Time Frame: Up to Day 7 (7 days post vaccination)
Up to Day 7 (7 days post vaccination)
Number of Maternal Participants with Unsolicited Adverse Events (AEs)
Time Frame: Up to Day 28 (28 days post vaccination)
Up to Day 28 (28 days post vaccination)
Number of Maternal Participants with Medically-Attended AEs (MAAEs)
Time Frame: Day 1 to Month 6 (6 months postdelivery)
Day 1 to Month 6 (6 months postdelivery)
Number of Maternal Participants with Adverse Events of Special Interest (AESIs)
Time Frame: Day 1 to Month 12 (12 months postdelivery)
Day 1 to Month 12 (12 months postdelivery)
Number of Maternal Participants with Serious Adverse Events (SAEs)
Time Frame: Day 1 to Month 12 (12 months postdelivery)
Day 1 to Month 12 (12 months postdelivery)
Number of Maternal Participants with AEs Leading to Discontinuation
Time Frame: Day 1 to Month 12 (12 months postdelivery)
Day 1 to Month 12 (12 months postdelivery)
Number of Maternal Participants With Pregnancy Outcomes
Time Frame: Day 1 to Month 12 (12 months postdelivery)
Pregnancy outcomes will include stillbirth, live birth, vaginal delivery, and cesarean section delivery.
Day 1 to Month 12 (12 months postdelivery)
Number of Infant Participants with MAAEs
Time Frame: Day 1 (birth) to Month 12
Day 1 (birth) to Month 12
Number of Infant Participants with AESIs
Time Frame: Day 1 (birth) to Month 12
Day 1 (birth) to Month 12
Number of Infant Participants with SAEs
Time Frame: Day 1 (birth) to Month 12
Day 1 (birth) to Month 12
Number of Infant Participants With Birth Outcomes
Time Frame: Day 1 (birth) to Month 12
Birth outcomes will include gestational age and anthropometric measurements.
Day 1 (birth) to Month 12

Secondary Outcome Measures

Outcome Measure
Time Frame
Geometric Mean Titer (GMT) of Serum RSV-A and RSV-B Neutralizing Antibodies in Maternal Participants
Time Frame: Day 1, Day 29, delivery, and Month 6 (6 months postdelivery)
Day 1, Day 29, delivery, and Month 6 (6 months postdelivery)
Geometric Mean Concentration (GMC) of Serum RSV-F Binding Antibodies in Maternal Participants
Time Frame: Day 1, Day 29, delivery, and Month 6 (6 months postdelivery)
Day 1, Day 29, delivery, and Month 6 (6 months postdelivery)
Geometric Mean Fold-Rise (GMFR) of Postbaseline/Baseline Neutralizing Antibody Titers and Binding Antibody Concentrations in Maternal Participants
Time Frame: Day 29, delivery, and Month 6 (6 months postdelivery)
Day 29, delivery, and Month 6 (6 months postdelivery)
Percentage of Maternal Participants With ≥4-fold Increase From Baseline in Neutralizing Antibody Titers and Binding Antibody Concentrations
Time Frame: Baseline up to Month 6 (6 months postdelivery)
Baseline up to Month 6 (6 months postdelivery)
GMT of Serum RSV-A and RSV-B Neutralizing Antibodies in Infant Participants
Time Frame: Day 1 (birth), and Months 2, 6, and 12
Day 1 (birth), and Months 2, 6, and 12
GMC of Serum RSV-F Binding Antibodies in Infant Participants
Time Frame: Day 1 (birth), and Months 2, 6, and 12
Day 1 (birth), and Months 2, 6, and 12

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

ModernaTX, Inc.

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

November 15, 2023

Primary Completion (Estimated)

May 27, 2026

Study Completion (Estimated)

May 27, 2026

Study Registration Dates

First Submitted

November 14, 2023

First Submitted That Met QC Criteria

November 19, 2023

First Posted (Actual)

November 22, 2023

Study Record Updates

Last Update Posted (Actual)

February 5, 2026

Last Update Submitted That Met QC Criteria

February 3, 2026

Last Verified

January 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • mRNA-1345-P201
  • 2023-505359-37-00 (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

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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