Beyfortus (nirsevimab) study published in The Lancet Infectious Diseases shows benefit for infants beyond first RSV season – Sanofi

A universal respiratory syncytial virus (RSV) immunization program using Beyfortus (nirsevimab) was associated with a statistically significant reduction in RSV-related hospitalizations in the second RSV season among infants immunized during their first season, according to a new study published in The Lancet Infectious Diseases. The NIRSE-GAL study, conducted in Galicia, Spain, is the first prospective real-world population study to evaluate the impact of a universal Beyfortus immunization program during two consecutive RSV seasons. The study findings, comparing the number of hospitalizations in immunized infants during their second RSV season versus the number of expected hospitalization cases based on data from recent seasons, are being presented at RSVVW ’26 (Respiratory Syncytial Virus Vaccines for the Word) conference in Rome, Italy.

The coverage rate was 94.4% among the cohort (11,796 infants out of 12,492 eligible) and the study showed a substantial reduction of 85.9% (95% confidence interval [CI] 80.2–90.0) in RSV-related lower respiratory tract infection (LRTI) hospitalizations during the first season. The study also showed 55.3% (95% CI 22.5-74.3) fewer hospitalizations in the second RSV season among infants who received a dose of Beyfortus during infancy. By preventing severe RSV infections during the first months of life, a critical period of lung development, it is thought the infants may be less prone to subsequent admissions from either RSV or other infections.

“This universal RSV immunization program with Beyfortus showed decreased RSV-related hospitalizations and outpatient illness burden during the first season, with persistent impact seen on RSV hospitalizations through the second season,” said Federico Martinón-Torres, Head of Pediatrics at Santiago University Hospital in Spain, and principal investigator of the NIRSE-GAL study. “These results offer compelling population-based data to inform infant immunization strategies and economic evaluation models.”

“This study builds upon our wealth of evidence supporting the public health value of a Beyfortus immunization program,” said Thomas Triomphe, Executive Vice President, Vaccines, Sanofi. “It’s exciting to see the significant impact of this infant immunization program during the first RSV season and truly remarkable to consider a benefit across two seasons.”

Further findings
The study also showed reductions in primary care consultations during the first RSV season, including:

• i) 30.8% (17.5-41.9) reduction in first consultations for acute bronchitis or bronchiolitis;
• ii) 33.4% (21.6-43.4) reduction in consultations for lower respiratory tract infections and;
• iii) 27.7% (14.9-38.5) reduction in consultations for wheezing or asthma.

Furthermore, rehospitalizations in infants previously hospitalized due to RSV decreased considerably during the second RSV season, with a 78.2% (25.6–93.6) reduction in RSV-related rehospitalizations and a 62.4% (30.9–79.6) reduction in LRTI rehospitalizations. These data support the hypothesis that early protection against RSV-related damage to the lungs may have lasting beneficial effects on respiratory health.

Citation: Impact of universal nirsevimab prophylaxis in infants on hospital and primary care outcomes across two respiratory syncytial virus seasons in Galicia, Spain (NIRSE-GAL): a population-based prospective observational study. Authors: Josefina L Razzini, MD ∙ Iago Giné-Vázquez, PhD ∙ Jing Jin, PhD. Published January 12, 2026. The Lancet Infectious Diseases. DOI: 10.1016/S1473-3099(25)00742-X