Maternal vaccination provides protection against RSV-associated hospitalization in early infancy

A study led by researchers at the University of Pittsburgh and UPMC published today in JAMA Network Open, a peer-reviewed journal of the American Medical Association, found that vaccination against respiratory syncytial virus (RSV) during pregnancy reduced the risk of hospitalization in young infants by nearly 70%.

This study provides early real-world evidence from U.S. clinical care, showing that administering one dose of the maternal RSV vaccine (RSVpreF vaccine) reduces hospitalization related to RSV in young infants. The results are consistent with findings from RSVpreF vaccine clinical trials. The RSVpreF vaccine was approved by the U.S. Food and Drug Administration in 2023.

We designed this study to focus on what matters most to families: whether their baby might end up in the hospital. The findings show a significant impact for families and for the health system, and it highlights how effective this intervention can be during the most vulnerable months of life."

Anne-Marie Rick, M.D., Ph.D., lead author of the study, assistant professor of pediatrics and clinical and translational science at Pitt School of Medicine and physician at UPMC Children's Hospital of Pittsburgh and UPMC Magee-Womens Hospital

RSV is the leading cause of hospitalization among infants in the United States. According to the Centers for Disease Control and Prevention (CDC), about 2 to 3 out of every 100 babies younger than 3 months are hospitalized each year due to RSV, with severe cases sometimes requiring oxygen support or mechanical ventilation. Until the RSVpreF vaccine's approval, there was no reliable way to protect healthy newborns from RSV starting at birth.

The study analyzed health records from infants 90 days old or younger who were hospitalized for respiratory illness in western Pennsylvania during the 2023–24 and 2024–25 RSV seasons. Researchers focused on infants who were tested for RSV and compared outcomes between those whose mothers received the vaccine during pregnancy and those whose mothers did not. Infants who received monoclonal antibody protection - a separate RSV prevention option administered after birth - were excluded.

Among infants younger than 3 months, maternal vaccination was associated with approximately 68% effectiveness against hospitalization for respiratory illness caused by RSV and 69% effectiveness against more severe lung infections also caused by the virus.

The results are part of an ongoing four-year study to evaluate the effectiveness of maternal RSV vaccination across multiple seasons. Researchers will continue to follow patients during the 2025–26 and 2026–27 RSV seasons, expanding the analysis to include infants up to 180 days old and assessing how long protection lasts.

"We're continuing to follow patients to understand how well this protection holds over time and across different groups," said Rick. "These kinds of real-world data are critical for helping families, clinicians, and policymakers make informed decisions about how best to protect infants."