Evaluating effectiveness of maternal RSV vaccination and nirsevimab for severe RSV-related illness in infants

A new study found that infants receiving maternal Respiratory Syncytial Virus (RSV) vaccination or Nirsevimab after birth had significantly lower RSV infection and health care use compared to unprotected infants. It also showed fewer severe complications in RSV-positive infants with prevention. These findings highlight the positive impact of RSV preventive measures in high-risk populations. Findings from the study will be presented at the Pediatric Academic Societies (PAS) 2026 Meeting, taking place April 24–27 in Boston.

RSV is a leading cause of respiratory infections and hospitalization in infants under 6 months in the United States. In 2023, the U.S. Food and Drug Administration approved two new preventive immunizations against RSV to protect infants: Pfizer’s Abrysvo, a maternal vaccine administered between 32 and 36 weeks of pregnancy, and Sanofi’s Nirsevimab (Beyfortus), a long-acting monoclonal antibody injection. Real-world data on their effectiveness remain limited, especially in high-risk and underserved groups. During October 2023, New York faced a “tripledemic” of RSV, influenza and COVID-19. Researchers analyzed hospitalizations, respiratory support, and 180-day outcomes following RSV infection, along with other circulating respiratory viruses.

“The disease burden of RSV in this young infant population is tremendous, leading to about half a million emergency room visits and over 100,000 hospital admissions every year,” said Uday Patil, MD, FAAP, Associate Chair of Pediatrics at NYC Health + Hospitals/Elmhurst, principal investigator and senior author of the study.

“Our study investigated the impact of these immunizations during their very first season after they became available on preventing RSV infection-related morbidities in infants under 6 months old in one of the most diverse and medically underserved neighborhoods in Queens, New York City, served by Elmhurst Hospital. We found a high uptake (>65%) of the maternal RSV vaccine (Abrysvo) among our pregnant patients and of infant immunization (Beyfortus) among newborns (>90%). This indicates strong patient confidence in the health care system within our vulnerable population.

“The rates of RSV infections, hospitalizations, and severity of illness all declined significantly among infants in our study, demonstrating the high effectiveness of both of these immunizations. Our findings yield pragmatic results, emphasizing that these new preventive strategies against RSV are game-changers and confirming the saying that ‘an ounce of prevention is worth a pound.”