Nirsevimab linked to large drops in infant RSV hospitalizations, study suggests

A population study reported that universal nirsevimab given to most infants was associated with about an 86% reduction in RSV-related hospitalizations in 2023–24 and a 55% reduction in 2024–25, with additional declines in clinic visits.

Researchers published a population-based analysis in The Lancet Infectious Diseases reporting that giving the long-acting monoclonal antibody nirsevimab to most infants sharply reduced hospitalizations and clinic visits linked to respiratory syncytial virus (RSV) during the 2023–24 season, and that some protection extended into the following season. The study followed 12,492 infants eligible for nirsevimab, and over 94% of eligible infants received the antibody. The analysis compared outcomes with RSV seasons before widespread nirsevimab use (2016–2023, excluding two pandemic years) and included related population studies from Italy and national data on risks for preterm children. Key findings: - RSV-related lower respiratory tract infection hospitalizations fell nearly 86% in 2023–24 and 55% in 2024–25 after widespread nirsevimab use. - First-time hospital admissions for LRTI, acute bronchitis, and bronchiolitis, plus outpatient visits for wheeze, asthma, and bronchitis/bronchiolitis, also declined in infants. - In Lombardy, Italy, a separate campaign that reached 79% of eligible infants was associated with a 42.7% drop in emergency visits and a 46.5% drop in hospitalizations for LRTI among infants in 2024–25. - All-cause hospitalization fell about 20% in the first season in the Spanish study but did not decline significantly in the second season. - CDC data reviewed separately show that preterm children accounted for about one in five RSV hospitalizations among those age 2 or younger and had higher risks of prolonged hospital stays and intensive care. Summary: The studies indicate large reductions in severe RSV illness and health-care visits among infants after widespread nirsevimab administration, with some evidence of protection into a second season. Undetermined at this time.