RSV Protection for Babies: ACOG Extends Maternal Vaccine Window to March as Real-World Data Shows Strong Protection

RSV remains the leading cause of infant hospitalization in the United States. As the 2026–27 season begins, two developments this week matter for parents: ACOG extended the recommended window for the maternal RSV vaccine (Abrysvo) through March 1, and fresh real-world evidence confirms it substantially reduces severe illness in babies. ## What changed ACOG’s 2026–27 respiratory virus immunization guidance, released earlier this season and highlighted in recent coverage, now recommends a single dose of Pfizer’s bivalent RSVpreF vaccine (Abrysvo) between 32 weeks 0 days and 36 weeks 6 days of gestation from September 1 through March 1 for patients without a planned delivery within two weeks. The previous window ended January 31. ACOG cites later-peaking and more severe recent RSV seasons as the reason for the extension. If the maternal vaccine is not given, infants can receive a monoclonal antibody (nirsevimab or clesrovimab) at birth. The maternal vaccine is given only once; in subsequent pregnancies the infant should receive the antibody. ## Real-world effectiveness A large review covering more than 4 million pregnancies found the maternal RSV vaccine reduced the risk of RSV-related hospitalization in babies under six months by approximately 74%, aligning with clinical trial results. Separate data presented at the 2026 Pediatric Academic Societies meeting showed infection rates of 1.7% among infants whose mothers received Abrysvo versus 7.9% among those without prevention, with markedly lower hospitalization and oxygen needs in the protected group. Uptake remains uneven. ACOG notes roughly 41.6% of eligible pregnant individuals have received the maternal RSV vaccine; other analyses put first-year U.S. uptake near 27%. Rates in Scotland and England have been higher in some periods. ## Competing viewpoints and practical notes Some public health discussions note that CDC parent-facing materials still describe a September–January window in many areas, while ACOG has extended to March 1. Clinicians generally follow the more recent ACOG guidance for timing. The vaccine is safe to co-administer with flu, Tdap, and COVID-19 vaccines. Mild side effects (arm pain, headache, muscle aches, nausea) are common and temporary. ## What parents should watch next - If you are 32–36 weeks pregnant between now and March 1 and have not received Abrysvo in a prior pregnancy, talk with your clinician about the maternal RSV vaccine. - If you deliver without having received it, ask about nirsevimab or clesrovimab for your newborn before hospital discharge. - Watch local RSV activity; seasons have been starting earlier or peaking later in recent years. - Continue routine hand hygiene and keep sick visitors away from newborns. Sources: ACOG 2026–27 immunization guidance and Practice Advisory on Maternal RSV Vaccination; Contemporary Pediatrics and Contemporary OB/GYN coverage of real-world data and the extended window (October 2026); University of Edinburgh / CIDRAP summary of multi-study effectiveness review.