ACOG Extends Maternal RSV Vaccine Window to March 1: Background, What Changed, and What Parents Should Watch

Background

RSV remains the leading cause of infant hospitalization in the United States. Protection options now include maternal vaccination during pregnancy with the bivalent RSV PreF vaccine (Abrysvo) and infant monoclonal antibodies (nirsevimab or clesrovimab) for those not protected by maternal antibodies.

Previous ACOG guidance limited maternal vaccination to September 1 through January 31. Recent seasons have peaked later—sometimes into February or beyond—prompting the change.

What changed

In its 2026-27 respiratory virus immunization recommendations, ACOG extended the maternal RSV vaccine window to March 1. Vaccination is still recommended between 32 0/7 and 36 6/7 weeks of gestation for patients without a planned delivery within two weeks. The vaccine is given once per pregnancy.

Effectiveness data cited in the guidance: maternal vaccination reduced infant hospitalization risk by 51% to 70%; nirsevimab reduced RSV-related hospitalization by 63.6% to 93% in the first season.

Competing viewpoints

Proponents of the extension argue it better matches observed seasonality and gives more flexibility for later-peaking seasons without weakening the recommendation. Some hospital systems and pediatric practices note ongoing challenges with monoclonal antibody supply, cost, and insurance coverage at the point of birth—issues that the window extension does not directly solve.

AAP’s parallel guidance expands second-season eligibility for certain high-risk children 8–19 months (preterm <32 weeks, significant congenital heart disease, anatomic pulmonary or neuromuscular issues, Down syndrome or similar chromosomal differences). Nirsevimab is currently the only product indicated for second-season use.

What to watch next

Sources: ACOG 2026-27 immunization guidance; AAP policy statement and technical report on RSV prevention for infants and children (published online September 2026, forthcoming in Pediatrics).

This is editorial context for expectant parents and caregivers, not medical advice. Confirm eligibility, timing, and product availability with your obstetrician, midwife, or pediatrician.