MSD announced US regulatory approval of Enflonsia (clesrovimab) for preventing respiratory syncytial virus (RSV) lower respiratory tract disease in infants entering their first RSV season. The single-dose monoclonal antibody (mAb) demonstrated 60.5% reduction in medically-attended RSV infections and 84.3% lower hospitalisation rates versus placebo in Phase IIb/III trials.

The weight-agnostic formulation offers season-long protection (up to 5 months) with shipments expected by July 2025 ahead of the RSV season. Approval was supported by CLEVER and SMART trials showing consistent efficacy across preterm and full-term infants.

The Advisory Committee on Immunization Practices (ACIP) was originally set to review usage recommendations later this month before being dissolved this week. It is unclear whether this will impact the product's launch.