The US Food and Drug Administration is evaluating a broader use of Merck’s long-acting RSV antibody, Enflonsia, aimed at shielding vulnerable children under 2 from severe disease across two RSV seasons, backed by positive phase 3 trial data.
The US Food and Drug Administration has accepted Merck’s application to broaden the use of Enflonsia, a long-acting respiratory syncytial virus antibody, for children younger than 2 who remain at elevated risk of severe disease into their second RSV season. The agency set a target decision date of March 22, 2027, while the European Medicines Agency took up a parallel filing for the same population in July 2026.
The move matters because RSV risk does not end after the first winter of life for every child. According to Merck, the proposed expansion would cover children with chronic lung disease of prematurity, congenital heart disease or certain premature birth-related risk factors. The filing is backed by the phase 3 SMART study, which included a first-season comparison with palivizumab and an open-label second-season dose in children who still met high-risk criteria.
Enflonsia was first cleared by the FDA in June 2025 for infants entering their first RSV season, and the European Commission followed in April 2026. The FDA’s trial snapshot describes it as a monoclonal antibody designed to provide about five months of protection after a single dose, a duration intended to cover a typical RSV season. Public health data also suggest broader prevention efforts are helping: the FDA has cited real-world surveillance from the 2024-2025 season showing infant RSV hospitalisations were lower than in pre-pandemic years, reflecting the combined impact of maternal vaccination and long-acting antibodies.
Disclaimer: This content is for informational purposes only and is not intended to be a substitute for professional medical judgment, advice, diagnosis, or treatment.
