University of Pittsburgh study finds RSV vaccination during pregnancy cuts infant hospitalizations by nearly 70%
PITTSBURGH - 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.
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.
"We designed this study to focus on what matters most to families: whether their baby might end up in the hospital," said lead author of the study, 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. "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."
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 2023-2024 and 2024-2025 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.
Studying the real-world impact of maternal vaccination presents a logistical challenge because it requires linking medical records from mothers and their infants, which are typically stored as separate patient records. Using integrated health data across UPMC's Western Pennsylvania network, researchers were able to connect these records and evaluate outcomes more comprehensively. "UPMC is really a unique place where we can do this type of work, as our connected system allows us to do it across a large population while maintaining the necessary rigor," added Rick.
How the vaccine protects newborns
Maternal RSV vaccination stimulates the pregnant person's immune system to produce antibodies against RSV. These antibodies cross the placenta before birth, helping protect infants from birth throughout early infancy, when they are most vulnerable. The vaccine is recommended between 32 and 36 weeks of pregnancy.
Because RSV is seasonal, the vaccine is typically given between September and January in most of the United States, according to the CDC.
Moreover, infants who are not protected at birth - either because their mothers did not receive the vaccine or received it too close to delivery for antibodies to be fully transferred -can receive a monoclonal antibody treatment after birth to prevent RSV. Clinical guidance recommends that infants receive one form of protection; both are generally not needed together.
"A few years ago, we didn't have any options to prevent RSV in newborns," said Rick. "Now we have two approaches - vaccination during pregnancy and antibody protection after birth - that give families and clinicians different ways to protect infants during their most vulnerable months."
Tracking long-term effectiveness across RSV seasons
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 2025-2026 and 2026-2027 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."
Frequently Asked Questions
Q: How effective is the RSV vaccine given during pregnancy?
A: This study suggests among infants younger than 3 months, the vaccine was 68% effectiveness against hospitalization for respiratory illness caused by RSV, and 69% effectiveness against more severe lung illness also caused by the virus.
Q: When during pregnancy should someone get the RSV vaccine?
A: The vaccine is recommended between 32 and 36 weeks of pregnancy, during RSV season (September through January in most of the United States), so antibodies have time to transfer to the baby before birth.
Q: Does a baby still need an RSV shot after birth if the mother was vaccinated?
A: In most cases, no. If the mother received the RSV vaccine at least 14 days before delivery, the infant typically does not need a separate monoclonal antibody. If the mother was not vaccinated, or the baby was born within 14 days of vaccination, the infant should receive a monoclonal after birth if they are born during RSV season.
Additional Resources
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Published study: Maternal Respiratory Syncytial Virus Prefusion F Vaccination and Acute Respiratory Illness in Infants
