Merck announced the USFDA approval of enflosina (clesrovimab-cfor) for preventing lower respiratory tract disease caused by respiratory syncytial virus (RSV) in newborns and infants entering their first RSV season. 

Enflosina is a long-acting monoclonal antibody that provides direct protection for up to 5 months—the typical length of an RSV season—with a single fixed 105 mg dose for all infants, regardless of weight. “RSV is the leading cause of infant hospitalizations in the U.S.,” said Dr. Octavio Ramilo, Chair of Infectious Diseases at St. Jude Children’s Research Hospital and investigator in the CLEVER and SMART trials. “ENFLONSIA’s efficacy and fixed-dose convenience make it a promising preventive option.” 

“ENFLONSIA offers a meaningful new option to protect infants, both healthy and at-risk, with a simple dosing regimen,” said Dr. Dean Y. Li, President, Merck Research Laboratories. “We aim to make it available in the U.S. before the upcoming RSV season.” 

The CDC’s Advisory Committee on Immunization Practices is expected to review ENFLONSIA later this month. Ordering is expected to begin in July, with distribution ahead of the 2025–2026 RSV season.