Can a second RSV shot in pregnancy protect more babies?

NCT ID NCT06866405

Disease control Sponsor: Pfizer Source: ClinicalTrials.gov ↗

First seen Jun 27, 2026 · Last updated Aug 14, 2026 · Updated 5 times

Summary

This study tests whether giving a second dose of an RSV vaccine to pregnant women who already received it in a prior pregnancy is safe and boosts immunity. About 550 women aged 18-49, between 24-36 weeks pregnant, will receive either the vaccine or a placebo. Researchers will track side effects and measure antibody levels in mothers and newborns to see how long protection lasts.

What this could mean

Our plain-language read of the trial. This is informational only, not medical advice or a prediction.

Active substance: RSVpreF (bivalent RSV vaccine)
What this could lead to: If successful, this could show that a second RSV vaccine dose during a later pregnancy is safe and boosts protection for newborns against severe RSV.
What could go wrong: This is an early-phase study focused on safety and immune response, not on preventing disease directly. The vaccine may not provide lasting protection or could cause side effects like pain or fever.

This is an AI summary of the original study and may miss details. Read our disclaimer.

Study facts

What this study's own registry entry says, in plain language.

Phase

Phase 3

Large-scale testing in a bigger group. Usually the last step before a treatment can be approved.

Participants

About 550 people

The number the study aims to enrol. It can still change while the study runs.

Started

Apr 2025

Expected to finish

Feb 2028

An estimate. End dates often move.

Lead sponsor

A company

The lead sponsor is a pharmaceutical, biotech, or medical-device company.

Who can take part

This study's own entry requirements. Only the study team can say for certain whether you qualify.

Ages

0 years and older

Sex

Anyone

Healthy volunteers

Accepted

You do not need to have the condition being studied to take part.

Show the full entry requirements

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Pregnant Participants-Cohort 1 and Cohort 2 Key Inclusion Criteria * Women aged 18 to 49 who are pregnant, between 24 and 36 weeks along, and expecting one baby without known risks for complications can participate. * Had the RSVpreF or Abrysvo vaccine during a previous pregnancy. * Had an ultrasound scan at 18 weeks or later during their current pregnancy, with no major fetal problems detected. * Based on their medical history, physical check-up, and the doctor's judgment, they are found suitable to join the study. * Agrees to let their baby take part in the study and gives their permission. * Able to sign a consent form, agreeing to follow the rules and conditions of the study. Key Exclusion Criteria * Received any approved or experimental RSV vaccine since their previous pregnancy. * Has a pre-pregnancy body mass index (BMI) over 40 kg/m2. * History of a severe bad reaction to a vaccine or a serious allergic reaction (like anaphylaxis) to any ingredient in the study vaccine or a similar vaccine. * Current pregnancy problems or issues at the time of giving consent. * Previous pregnancy issues or problems at the time of giving consent. * Women who are breastfeeding at the time of enrollment Infant Participants * Proof that the parent(s) or legal guardian(s) has signed and dated a consent form. * Parent(s) or legal guardian(s) must agree to attend scheduled visits and follow the study plan, including laboratory tests and other procedures. Nonpregnant Participants-Cohort 3 Key Inclusion Criteria * Have already received one dose of the RSVpreF vaccine during their previous pregnancy as part of the Pfizer clinical trial, and the results from that time can be used for this study. * Able to sign a consent form, agreeing to follow the rules and requirements of the study. Key Exclusion Criteria * Received any approved or experimental RSV vaccine after participating in the Pfizer clinical trial. * Taking part in other studies with new drugs within 28 days before giving consent or during the study period.

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Conditions

The condition(s) this trial relates to.

respiratory syncytial virus infectious disease prevention target

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

RSV infection

How to take part

Only the study team decides who joins. These are the ways to reach them.

The places running it

96 sites in 4 countries. The list below names each one and where it is.
The official record

ClinicalTrials.gov lists the study team's own contact details, including names and phone numbers. We don't republish those.

Open the record ↗
A doctor treating you

A doctor who knows your case can contact a study site on your behalf, and can tell you whether this study is worth pursuing at all.

Contacts and locations

Locations

Accellacare - McFarland
RECRUITING

Ames, Iowa, 50010, United States
Advanced Specialty Research
RECRUITING

Boise, Idaho, 83702, United States
Anschutz Health Sciences Building (AHSB)
RECRUITING

Aurora, Colorado, 80045, United States
Boeson Research GTF
RECRUITING

Great Falls, Montana, 59405, United States
Boeson Research KAL
RECRUITING

Kalispell, Montana, 59901, United States
Boeson Research Laboratory
RECRUITING

Missoula, Montana, 59804, United States
Boeson Research MSO
RECRUITING

Missoula, Montana, 59804, United States
Boston Medical Center
RECRUITING

Boston, Massachusetts, 02118, United States
CU Research Pharmacy
RECRUITING

Aurora, Colorado, 80045, United States
Center for Research in Women's Health
RECRUITING

Birmingham, Alabama, 35233, United States
Centro de investigación Clínica OSECAC - Sede Jonas Salk
RECRUITING

Buenos Aires, 1044, Argentina
Children's Hospital Colorado
RECRUITING

Aurora, Colorado, 80045, United States
Children's of Alabama
RECRUITING

Birmingham, Alabama, 35233, United States
Cincinnati Children's Hospital Medical Center
RECRUITING

Cincinnati, Ohio, 45229, United States
Citadelle Clinical Research
RECRUITING

North Miami Beach, Florida, 33162, United States
Clinica Del Niño Y La Madre
RECRUITING

Mar del Plata, Buenos Aires, 7600, Argentina
Clinical Research Partners, LLC
RECRUITING

Richmond, Virginia, 23226, United States
Clinical Research Prime
RECRUITING

Idaho Falls, Idaho, 83404, United States
Clínica Mayo de Urgencias Médicas Cruz Blanca S.R.L
RECRUITING

San Miguel de Tucumán, Tucumán Province, 4000, Argentina
Duke University - Main Hospital and Clinics
RECRUITING

Durham, North Carolina, 27705, United States
Duke University - Main Hospital and Clinics
RECRUITING

Durham, North Carolina, 27710, United States
Emerald Coast OBGYN Clinical Research
RECRUITING

Panama City, Florida, 32405, United States
Emerald Coast Pediatrics
RECRUITING

Panama City, Florida, 32405, United States
Equipo Ciencia
RECRUITING

Buenos Aires, C1428BNF, Argentina
Family Clinical Research Unit (Fam-Cru)
RECRUITING

Cape Town, Western Cape, 7500, South Africa
Fundación Respirar
RECRUITING

Ciudad Autónoma de Buenos Aires, Buenos Aires, C1426ABP, Argentina
HCA Florida Gulf Coast Hospital
RECRUITING

Panama City, Florida, 32405, United States
Heart & Hands Midwifery
RECRUITING

Kalispell, Montana, 59901, United States
Helios Clinical Research - WEA
RECRUITING

Weatherford, Texas, 76086, United States
Hospital Público Materno Infantil
RECRUITING

Salta, 4400, Argentina
Infusion Solutions, LLC
RECRUITING

Richmond, Virginia, 23226, United States
Instituto de Maternidad y Ginecología Nuestra Señora de las Mercedes
RECRUITING

San Miguel de Tucumán, Tucumán Province, 4000, Argentina
Into Research
RECRUITING

Pretoria, Gauteng, 0181, South Africa
Josha Research
RECRUITING

Bloemfontein, Free State, 9301, South Africa
Lovelace Women's Hospital
RECRUITING

Albuquerque, New Mexico, 87109, United States
Lucile Packard Children's Hospital-Labor and Delivery Unit
RECRUITING

Palo Alto, California, 94304, United States
MRC Unit on Child And Adolescent Health
RECRUITING

Cape Town, Western Cape, 7700, South Africa
Mary Greeley Medical Center
RECRUITING

Ames, Iowa, 50010, United States
McFarland Clinic, PC
RECRUITING

Ames, Iowa, 50010, United States
Medical City Weatherford
RECRUITING

Weatherford, Texas, 76086, United States
Medical Research Council Unit
RECRUITING

Banjul, Fajara, PO Box 273, The Gambia
Memorial Hermann Memorial City Hospital
RECRUITING

Houston, Texas, 77024, United States
OBGYN Associates
RECRUITING

Great Falls, Montana, 59405, United States
Origin Health
RECRUITING

Missoula, Montana, 59804, United States
Presbyterian Hospital
RECRUITING

Albuquerque, New Mexico, 87107, United States
Prisma Health
RECRUITING

Greenville, South Carolina, 29605, United States
Prisma Health-Upstate
RECRUITING

Greenville, South Carolina, 29605, United States
Ronald Reagan UCLA Medical Center
RECRUITING

Los Angeles, California, 90024, United States
Ronald Reagan UCLA Medical Center
RECRUITING

Los Angeles, California, 90095, United States
Ronald Reagan UCLA Medical Center (inpatient hospital)
RECRUITING

Los Angeles, California, 90095, United States
Saint Alphonsus Medical Center
RECRUITING

Nampa, Idaho, 83687, United States
Saint Alphonsus Regional Medical Center
RECRUITING

Boise, Idaho, 83706, United States
Seattle Children's Hospital
RECRUITING

Seattle, Washington, 98105, United States
Seattle Children's Research Institute
RECRUITING

Seattle, Washington, 98101, United States
Sentara Leigh Hospital
RECRUITING

Norfolk, Virginia, 23502, United States
Setshaba Research Centre
RECRUITING

Pretoria, Gauteng, 0152, South Africa
St. Luke's Boise Medical Center
RECRUITING

Boise, Idaho, 83712, United States
St. Luke's Nampa Medical Center
RECRUITING

Nampa, Idaho, 83687, United States
Stanford Obstetrics Clinic
RECRUITING

Palo Alto, California, 94304, United States
Stanford University
RECRUITING

Palo Alto, California, 94304, United States
Stanford University Medical Center
RECRUITING

Palo Alto, California, 94304, United States
The Group For Women - Kempsville Office
RECRUITING

Norfolk, Virginia, 23502, United States
The University of Texas Health Science Center at Houston
RECRUITING

Houston, Texas, 77204, United States
Tidewater Physicians for Women
RECRUITING

Norfolk, Virginia, 23502, United States
UCLA
RECRUITING

Los Angeles, California, 90095, United States
UCLA (outpatient clinic)
RECRUITING

Los Angeles, California, 90095, United States
UCLA Clinical and Translational Research Center (research clinic)
RECRUITING

Los Angeles, California, 90095, United States
UNM Hospital
RECRUITING

Albuquerque, New Mexico, 87107, United States
USA Health Children's and Women's Hospital
RECRUITING

Mobile, Alabama, 36604, United States
USA Health Strada Patient Care Center
RECRUITING

Mobile, Alabama, 36604, United States
University of Alabama at Birmingham - School of Medicine
RECRUITING

Birmingham, Alabama, 35233, United States
University of Alabama at Birmingham Women & Infants Center
RECRUITING

Birmingham, Alabama, 35233, United States
University of Cape Town Lung Institute (Pty) Ltd
RECRUITING

Cape Town, Western Cape, 7700, South Africa
University of Colorado AO1 UCH
RECRUITING

Aurora, Colorado, 80045, United States
University of Colorado Hospital Inpatient Pavilion
RECRUITING

Aurora, Colorado, 80045, United States
University of Colorado Hospital Outpatient Pavilion
RECRUITING

Aurora, Colorado, 80045, United States
University of Colorado Research II Building
RECRUITING

Aurora, Colorado, 80045, United States
University of Kansas Medical Center
RECRUITING

Kansas City, Kansas, 66160, United States
University of Utah
RECRUITING

Salt Lake City, Utah, 84112, United States
University of Utah
RECRUITING

Salt Lake City, Utah, 84132, United States
University of Utah Clinical Neuroscience Center
RECRUITING

Salt Lake City, Utah, 84132, United States
University of Utah Hospital
RECRUITING

Salt Lake City, Utah, 84132, United States
University of Utah Madsen Health Center - Women's Health
RECRUITING

Salt Lake City, Utah, 84112, United States
University of Utah Obstetrics and Gynecology Research Offices
RECRUITING

Salt Lake City, Utah, 84108, United States
University of Washington - Northwest
RECRUITING

Seattle, Washington, 98133, United States
University of Washington Medical Center - Montlake
RECRUITING

Seattle, Washington, 98195, United States
University of Witwatersrand (WITS) - Vaccines and Infectious Diseases Analytics (VIDA)
RECRUITING

Johannesburg, Gauteng, 1864, South Africa
Velocity Clinical Research - New Orleans
RECRUITING

New Orleans, Louisiana, 70119, United States
Velocity Clinical Research, Albuquerque
RECRUITING

Albuquerque, New Mexico, 87107, United States
Velocity Clinical Research, Grand Island
RECRUITING

Grand Island, Nebraska, 68803, United States
Velocity Clinical Research, Gulfport
RECRUITING

Gulfport, Mississippi, 39503, United States
Velocity Clinical Research, Norfolk
RECRUITING

Norfolk, Nebraska, 68701, United States
Virginia Physicians For Women (VPFW)
RECRUITING

North Chesterfield, Virginia, 23235, United States
Weatherford OB/GYN Associates
RECRUITING

Weatherford, Texas, 76086, United States
Wits RHI
RECRUITING

Johannesburg, Gauteng, 2001, South Africa
WomensCare Center
RECRUITING

Norfolk, Virginia, 23502, United States

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