A new study, conducted by researchers from the University of Pittsburgh and UPMC and published in JAMA Network Open, has found that infants born to vaccinated mothers were significantly less likely to be hospitalised due to RSV infection during the first few months of life.
The study holds importance in the context of India, where Respiratory Syncytial Virus (RSV) is a leading cause of lower respiratory tract infections, particularly for infants under two years old. It accounts for over 1,00,000 paediatric hospitalisations annually. For many, it turns out to be fatal too.
Despite often being confused with a seasonal cold, RSV is linked to approximately 3.6 million hospitalisations and nearly 1,00,000 deaths annually in children below five years worldwide.
Researchers reported that maternal vaccination was associated with a nearly 70 per cent reduction in RSV-related hospitalisations among infants younger than three months. The protective effect was also observed against more severe lung infections caused by the virus.
The findings are consistent with results previously reported from clinical trials of the RSVpreF vaccine, which received approval from the U.S. Food and Drug Administration in 2023. However, unlike controlled trials, the current study examined outcomes in routine healthcare settings, offering insights into how the vaccine performs in everyday clinical practice.
“We designed this study to focus on what matters most to families: whether their baby might end up in the hospital,” said Anne-Marie Rick, lead author of the study, assistant professor of paediatrics 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.”
According to the U.S. Centers for Disease Control and Prevention (CDC), RSV remains the leading cause of infant hospitalisation in the country. Each year, approximately two to three out of every 100 babies younger than three months require hospital care because of RSV infection. Prior to the availability of maternal vaccination, preventive options for healthy newborns were extremely limited.
To assess vaccine effectiveness, investigators analysed medical records of infants aged 90 days or younger who were admitted to hospitals in western Pennsylvania with respiratory illnesses during the 2023–24 and 2024–25 RSV seasons. The analysis compared infants whose mothers received the vaccine during pregnancy with those whose mothers remained un-vaccinated.
Researchers excluded infants who had received monoclonal antibody prophylaxis after birth, another preventive strategy currently available against RSV, to ensure a clearer assessment of the vaccine's impact.
One of the major challenges in studying maternal vaccination is linking health records of mothers and babies, which are generally maintained separately. The integrated healthcare network operated by UPMC enabled researchers to connect these records and evaluate outcomes across a large patient population.
“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 rigour,” added Rick.
Experts note that maternal immunisation works by generating protective antibodies in the pregnant individual. These antibodies cross the placenta before delivery and provide passive immunity to the infant immediately after birth.
Current recommendations advise administering the vaccine between 32 and 36 weeks of pregnancy. Because RSV follows a seasonal pattern, vaccination is generally offered during periods when virus circulation is expected to be highest.
For infants who do not receive protection through maternal vaccination—either because the mother was not vaccinated or because vaccination occurred too close to delivery—another preventive option exists in the form of long-acting monoclonal antibodies administered after birth. Clinical guidance currently recommends that infants receive either maternal vaccine-derived protection or monoclonal antibody protection, rather than both.
“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.”
The newly reported findings form part of a larger four-year research programme examining the effectiveness of maternal RSV immunisation over multiple respiratory virus seasons. Investigators plan to continue monitoring outcomes during the 2025–26 and 2026–27 seasons.
Future analyses will extend follow-up to infants up to six months of age and examine how long vaccine-derived protection persists. Researchers also hope to determine whether effectiveness varies across different infant populations and clinical settings.
“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.”
The WHO’s SAGE advisory group recommends RSV vaccination during the third trimester to maximise antibody transfer to the unborn child.
