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Revaccination with RSV vaccine during subsequent pregnancies

A Phase 3 Study to Investigate the Safety, Tolerability, and Immunogenicity of Revaccinating Pregnant Participants During Subsequent Pregnancies and Persistence of Immunity of a Single Dose of a Bivalent Respiratory Syncytial Virus (RSV) Vaccine.

Phase 3 Interventional Pfizer · NCT06866405

This study is testing if giving a second dose of the RSV vaccine to pregnant women who already had it is safe and effective for them and their babies.

Quick facts

PhasePhase 3
Study typeInterventional
Enrollment550 (estimated)
Ages0 Years and up
SexAll
SponsorPfizer Industry-sponsored
Locations94 sites (Birmingham, Alabama and 93 other locations)
Trial IDNCT06866405 on ClinicalTrials.gov

What this trial studies

This study evaluates the safety and tolerability of a second dose of the RSVpreF vaccine in pregnant women who previously received the vaccine. It includes two cohorts of pregnant participants: one receiving the second dose and another randomly assigned to receive either the vaccine or a placebo. Additionally, non-pregnant participants will have their blood analyzed to assess the duration of immunity from a prior vaccination. The study aims to monitor the immune response and safety for both mothers and their infants over a six-month period post-birth.

Who should consider this trial

Good fit: Ideal candidates are pregnant women aged 18 to 49 who are between 24 and 36 weeks along and have previously received the RSVpreF vaccine.

Not a fit: Patients who have received any RSV vaccine since their last pregnancy or have a history of severe allergic reactions to vaccines may not benefit from this study.

Why it matters

Potential benefit: If successful, this study could enhance maternal and infant protection against RSV infections through improved vaccination strategies.

How similar studies have performed: Other studies have shown promise in maternal immunization against RSV, indicating potential for success with this approach.

Eligibility criteria

Show full inclusion / exclusion criteria 
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.

Where this trial is running

Birmingham, Alabama and 93 other locations

+44 more sites — see ClinicalTrials.gov for the full list.

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions RSV InfectionPregnancyRSV vaccineRSVMaternal immunization
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.