The RSV Vaccine in Pregnancy

Abrysvo — approved in 2023, now routinely offered at 32 to 36 weeks; what the clinical trial found and what belongs in the consent conversation

Full Drug Card → Abrysvo Maternal RSV Vaccine

As of 2023, a vaccine called Abrysvo is routinely offered to pregnant women at 32 to 36 weeks. Your provider may introduce it as “protection against RSV for your baby.” RSV — respiratory syncytial virus — is a real illness that sends thousands of infants to the hospital each year. The vaccine’s benefit is documented. What is almost never disclosed: this vaccine was approved less than two years before it became a routine recommendation, the clinical trial found a higher rate of preterm births in vaccinated women, the vote to recommend it was 11 to 1, and if your baby also receives a separate RSV antibody injection at birth, the combination of both has not been studied. You have the right to know all of this before you decide.

What it is

The Basics

Product name

Abrysvo (Pfizer)
FDA-approved August 2023
Given at 32 to 36 weeks gestation
Single intramuscular injection

What it contains

Bivalent RSVpreF protein antigen (a fragment of the RSV spike protein)
No adjuvant
No thimerosal
Sucrose, mannitol, tromethamine buffer

How it works

Abrysvo works through placental antibody transfer. When you receive the vaccine, your immune system produces antibodies against RSV. Those antibodies cross the placenta and enter your baby’s bloodstream, providing protection against RSV in the first months of life before your baby can be vaccinated themselves.

RSV (respiratory syncytial virus) is a common respiratory virus that causes cold-like symptoms in adults and older children, but can cause bronchiolitis — inflammation and mucus blockage in the small airways — in very young infants. Approximately 58,000–80,000 children under 5 are hospitalized with RSV each year in the US. Premature infants, infants with heart or lung conditions, and immunocompromised infants are at highest risk.

The trial & the approval

What the MATISSE Trial Found

■Efficacy: The MATISSE phase 3 trial found 81.8% efficacy against severe RSV-associated lower respiratory tract disease in infants in the first 90 days of life. This is a meaningful protection signal, particularly for infants born prematurely or into winter RSV season.
■Preterm birth rate: The trial found a higher rate of preterm births in the Abrysvo group compared to placebo — 5.3% in the vaccinated group versus 4.9% in the placebo group. This difference was flagged by the FDA advisory committee. A Data Safety Monitoring Board (DSMB) temporarily halted enrollment to review it, then concluded the trial should continue. The Abrysvo package insert states this finding directly.
■ACIP vote: The Advisory Committee on Immunization Practices voted 11-1 to recommend Abrysvo for all pregnant women at 32–36 weeks. The single dissenting vote was based on the preterm birth signal. A close vote on a safety concern in a vaccine recommended to all pregnant women is not disclosed at the point of administration.
■Approval date: August 2023. The routine recommendation to all pregnant women followed within months. Women who received this vaccine in 2023 and 2024 were among the first to do so at any scale.

What no one mentions

The Dual-Antibody Question

Abrysvo + Beyfortus at birth — a combination not studied before being recommended

In the same 2023 season that ACIP recommended Abrysvo for pregnant women, they also recommended Beyfortus (nirsevimab) — a monoclonal antibody injection — for newborns at birth. These are two different RSV antibody products designed for the same purpose.

If you receive Abrysvo during pregnancy, you will transfer RSV antibodies to your baby through the placenta. If your hospital then also gives your baby Beyfortus at birth, your infant receives a second, separate source of RSV antibodies on top of what you already transferred.

These two products were simultaneously recommended in the same season. The safety and immunological effects of having both maternal-transferred antibodies from Abrysvo and injected nirsevimab from Beyfortus in the same infant were not studied in a clinical trial before both were recommended together. This is not a theoretical concern — it is a documented gap in the evidence base, and it is not disclosed when either product is offered.

The timeline matters

When You Receive It Shapes What It Protects Against

32–36 weeks

You receive Abrysvo. Your immune system produces anti-RSV antibodies over the following weeks. These transfer to the fetus through the placenta.

At birth

Your baby is born with your transferred RSV antibodies. If born into RSV season (typically October–March), protection is most relevant immediately. If born in spring, the antibody levels will have declined significantly by the following winter season.

First winter RSV season

If your baby was born in spring or early summer and did not receive Beyfortus, maternal antibodies from the Abrysvo shot may have waned substantially by the time your baby faces their first winter RSV season. The protection window from a maternal vaccine given at 32 weeks is not indefinite.

Before you decide

Questions to Bring to Your Provider

Can I see the package insert for Abrysvo? What does it say specifically about the preterm birth finding in the MATISSE trial?
The ACIP vote to recommend this vaccine was 11–1. What was the basis of the dissenting vote, and how is the preterm birth signal being monitored in post-approval surveillance?
If my baby also receives Beyfortus at birth, has the combination of maternal-transferred Abrysvo antibodies and injected nirsevimab been studied in the same infant? What is the expected effect?
My baby is expected to be born in [month]. Given when I would receive the vaccine and when my baby will face their first RSV season, how much protection will actually be present at the relevant time?
What is my individual risk profile for having a baby who develops serious RSV illness — gestational age, birth season, any cardiac or pulmonary risk factors?
This vaccine was approved in August 2023. What post-approval safety surveillance data is available, and where can I access it?