How Enflonsia Protects Infants from RSV Disease
Enflonsia is a long-acting monoclonal antibody given as one intramuscular dose to help prevent RSV lower respiratory tract disease during an infant’s first RSV season.
Timeline
- June 9, 2025: The FDA approved Enflonsia, also known as clesrovimab-cfor.
- First RSV season: The approved use covers newborns and infants born during or entering that season.
The U.S. Food and Drug Administration approved Enflonsia, the brand name for clesrovimab-cfor, on June 9, 2025. It is indicated to prevent respiratory syncytial virus lower respiratory tract disease in newborns and infants who are born during or entering their first RSV season. [1][2]
Enflonsia is a monoclonal antibody rather than a traditional vaccine. It supplies a laboratory-produced antibody that can bind RSV, giving the infant passive protection. A vaccine generally trains the recipient’s immune system to produce its own response. That distinction explains why antibody protection can begin without waiting for an infant to build immunity. [1][2]
The labeled regimen is a single 105-milligram intramuscular injection, supplied as 105 milligrams in 0.7 milliliters. The dose does not change with infant weight under the approved instructions. FDA’s label states that protection demonstrated in clinical trials extended through five months after one dose. [1][2]
FDA based the approval on two main trials. Trial 004 compared one Enflonsia dose with saline placebo in preterm and full-term infants and evaluated medically attended RSV lower respiratory infection through day 150. Trial 007 compared it with palivizumab in infants at increased risk, including some born prematurely or with specified heart or lung conditions. [1]
The medicine reduces risk; it does not guarantee that an infant cannot acquire RSV, and it is not a treatment for an infection already underway. Its approved purpose is prevention of RSV lower respiratory tract disease for the defined infant population. Questions about timing and eligibility require the current prescribing information and a clinician. [1][2]
The prescribing information lists injection-site redness, injection-site swelling and rash as the most common adverse reactions in the clinical studies. It also describes hypersensitivity precautions and contraindicates use in an infant with a history of a serious hypersensitivity reaction, including anaphylaxis, to any component of Enflonsia. [2]
RSV options can differ by age, season, maternal vaccination history, health status and current public-health recommendations. Enflonsia’s FDA approval establishes what the product may be used for in the United States, while recommendations about who should receive an RSV preventive product and when can be updated separately by health authorities. [1][2]