RSV vaccine during pregnancy slashed risk of hospitalization for infants, study shows

A single dose of the maternal respiratory syncytial virus (RSVpreF vaccine) during pregnancy reduced the risk of infant hospitalization by nearly 70%, according to ongoing research results published recently in JAMA Network Open.

The study, titled ‘Maternal Respiratory Syncytial Virus Prefusion F Vaccination and Acute Respiratory Illness in Infants Link,’ was conducted by researchers at the University of Pittsburgh and UPMC. The study’s lead author was Anne-Marie Rick, M.D., Ph.D., assistant professor of pediatrics and clinical and translational science at Pitt School of Medicine and a physician at UPMC Children’s Hospital of Pittsburgh and UPMC Magee-Womens Hospital.

“We designed this study to focus on what matters most to families: whether their baby might end up in the hospital,” Rick said in a news release. “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.”

The RSVpreF vaccine was approximately 68% effective against hospitalization from RSV-related respiratory illness. Additionally, it was also approximately 69% effective against more severe lung infections associated with the virus, Rick and her team found. The vaccine — marketed by Pfizer under the brand name Abrysvo — works by prompting the mother's immune system to produce antibodies that cross the placenta and provide protection to the newborn from birth. This mechanism is especially critical because newborns cannot yet receive most vaccines on their own. If an infant’s mother is not vaccinated against RSV during pregnancy, infants younger than eight months of age born during RSV season or entering their first RSV season can receive a monoclonal antibody shot, according to the Centers for Disease Control and Prevention. The shot is not the same as a vaccine because it does not activate the infant’s immune system.

The study examined health records from 274 infants 90 days old or younger, hospitalized with a respiratory illness in the Western Pennsylvania area during the 2023–24 and 2024–25 RSV seasons. Researchers compared outcomes between infants whose mothers received the vaccine during pregnancy and those whose mothers did not.

Researchers write that the results are consistent with the biological plausibility that vaccines given earlier in gestation are more effective than those given later.

“As postmarketing safety data continue to accrue, modest expansion of the recommended vaccination window in the US to include earlier vaccination in pregnancy may optimize protection against RSV for infants born to vaccinated mothers,” the authors write in the study.

The CDC estimates that 2 in 3 infants ages three months and younger are hospitalized every year with RSV, with more serious cases potentially requiring oxygen support.

The vaccine was approved by the FDA in 2023. The current findings are part of a broader, ongoing four-year study. Researchers plan to continue tracking patients during the 2025–26 and 2026–27 RSV seasons, with plans to expand the analysis to include infants up to 180 days old to better assess how long maternal vaccination protection lasts.

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

This study was funded in part by a collaboration between Pfizer Inc. and the University of Pittsburgh.