FDA Approves Clesrovimab for RSV LRTD Prevention in Infants: Daily Dose

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On June 10, 2025, we reported on the US FDA approval of clesrovimab-cfor (Enflonsia, Merck) for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease (LRTD) in neonates and infants entering their first RSV season.

The approval

The approval marks the first non-weight-based RSV preventive monoclonal antibody available for this population.

The FDA based its approval on data from 2 key phase 3 trials in which clesrovimab demonstrated clinically meaningful reductions in RSV-associated disease severity and hospitalizations. In the Phase 2b/3 CLEVER trial (N = 3,614), clesrovimab reduced the incidence of RSV-associated medically attended lower respiratory infections (MALRI) by 60.5% compared to placebo and RSV-associated hospitalizations by 84.3%. Efficacy increased with disease severity.

The CLEVER trial investigators enrolled preterm and full-term infants up to age 1 year one year old and showed that a single dose of clesrovimab provided protection throughout the RSV season. The safety profile was comparable to placebo, with most adverse reactions being mild or moderate.

Clesrovimab is intended for use from birth for infants born during the RSV season, or prior to the season for those born earlier. A second dose is recommended following cardiopulmonary bypass in infants undergoing cardiac surgery during RSV season. Coadministration with routine pediatric vaccines has not shown any new safety concerns.

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