What Was Approved?
On June 9, 2025, the U.S. Food and Drug Administration approved Enflonsia (clesrovimab-cfor) to prevent respiratory syncytial virus, or RSV, lower respiratory tract disease in neonates and infants who are born during or entering their first RSV season.
Enflonsia is a preventive antibody treatment, not a treatment for an active RSV infection.
How Does Enflonsia Work?
Enflonsia is an RSV F protein-directed monoclonal antibody.
It binds to the RSV fusion protein and helps prevent the virus from entering susceptible cells.
How Is Enflonsia Given?
The recommended dose is:
105 mg by a single intramuscular injection.
For infants born during RSV season, it can be given beginning at birth. For infants born outside the season, it is given before their first RSV season.
What Are the Common Side Effects?
The most common adverse reactions were:
- Injection-site redness
- Injection-site swelling
- Rash
What Is an Important Safety Concern?
Serious hypersensitivity reactions, including anaphylaxis, are possible.
Enflonsia is contraindicated in infants with a history of serious hypersensitivity to any component of the product.
Is Enflonsia Approved for Older Children?
The FDA label states that safety and effectiveness have not been established in children older than 12 months.
Bottom Line
Enflonsia (clesrovimab-cfor) is an FDA-approved single-dose monoclonal antibody used to prevent RSV lower respiratory tract disease in infants entering their first RSV season.
It is preventive therapy and should not be confused with treatment for an active RSV infection.
Sources
- U.S. Food and Drug Administration (FDA) — Drug Trials Snapshot: Enflonsia.
- U.S. Food and Drug Administration (FDA) — Enflonsia Prescribing Information, June 2025.
- U.S. Food and Drug Administration (FDA) — Novel Drug Approvals for 2025.