The U.S. Food and Drug Administration (FDA) has approved the first vaccine designed to protect infants against respiratory syncytial virus (RSV) by vaccinating pregnant individuals. The bivalent RSVpreF vaccine, marketed as Abrysvo by Pfizer, is indicated for administration at 32 through 36 weeks of gestational age to prevent lower respiratory tract disease in infants from birth through six months of age.
How does the maternal RSV vaccine function?
The vaccine works by inducing the production of maternal antibodies that cross the placenta. According to the FDA’s official approval announcement, these antibodies provide passive immunity to the fetus, protecting the newborn during their most vulnerable months. By vaccinating the parent during the third trimester, the infant receives immediate protection upon birth, effectively bridging the gap until the child can develop their own immune response.
What do the clinical trials show?
The regulatory decision was based on data from the MATISSE clinical trial, a randomized, double-blind, placebo-controlled study published in the New England Journal of Medicine.
In this trial, 3,682 pregnant individuals received the vaccine, while 3,676 received a placebo. The study found that the vaccine was 81.8% effective at preventing severe medically attended lower respiratory tract illness in infants within 90 days after birth. By 180 days, the efficacy rate was 69.4%. The most commonly reported side effects in pregnant participants included injection-site pain, headache, muscle pain, and nausea.
Who should receive the vaccine?
The Centers for Disease Control and Prevention (CDC) recommends that the vaccine be administered during the 32 through 36-week gestational window. This timing is critical to ensure that the infant receives a sufficient transfer of antibodies before delivery.
The CDC notes that this maternal vaccination is one of two primary ways to protect newborns from RSV. The other option is the administration of nirsevimab (Beyfortus), a monoclonal antibody injection given directly to the infant after birth. The CDC advises that in most cases, infants do not need both protections; healthcare providers are encouraged to discuss which option is most appropriate based on the infant’s birth timing and the local RSV season.
Why is this development significant?
RSV is a common respiratory virus that causes mild, cold-like symptoms in most adults but can lead to severe illness in infants, including bronchiolitis and pneumonia. Before the availability of these preventive measures, RSV was a leading cause of hospitalization for infants in the United States.
Prior to this approval, there were no vaccines available to protect infants against RSV. The introduction of Abrysvo provides a new tool for clinical practice, shifting the focus from treating RSV-related hospitalizations to preventing them entirely through prenatal intervention.
Frequently Asked Questions
- Is the vaccine safe for the pregnant person? Clinical trials monitored for adverse events, and the FDA concluded that the benefits of preventing severe RSV disease in infants outweigh the potential risks.
- Can the vaccine be given before 32 weeks? The FDA-approved labeling specifies the 32 through 36-week window to optimize antibody transfer and avoid potential risks associated with preterm birth.
- Does the vaccine protect the infant for their whole life? No. The immunity provided is passive and temporary, designed specifically to protect the infant during the first six months of life when they are at the highest risk for severe complications.