RSV Prevention: FDA Approves Clesrovimab for Infants
- The Food and Drug Administration has given the green light to Enflonsia (clesrovimab-cfor), a monoclonal antibody designed to protect newborns from respiratory syncytial virus (RSV), Merck announced.
- Jude’s Children’s Research Hospital and a principal investigator for Merck, emphasized the significance of this approval.
- Results showed that a single dose of clesrovimab reduced RSV-related lower respiratory infections requiring medical attention by 60.5% over a five-month period, compared to a placebo.
The FDA has approved Enflonsia (clesrovimab), offering a new defense against RSV for newborns. This monoclonal antibody, developed by Merck, promises to simplify administration with a fixed dose, contrasting with weight-based options. News Directory 3 reports this significant progress, noting a phase 2b/3 trial showed a 60.5% reduction in RSV-related lower respiratory infections, and an 84.3% cut in hospitalizations. This approval, supported by compelling clinical data, provides a promising intervention, joining nirsevimab.Learn whether the CDC’s upcoming recommendations will shape the future of RSV prevention. discover what’s next …
FDA Approves Enflonsia for RSV Prevention in Infants
Updated June 10, 2025
The Food and Drug Administration has given the green light to Enflonsia (clesrovimab-cfor), a monoclonal antibody designed to protect newborns from respiratory syncytial virus (RSV), Merck announced. The company plans to make Enflonsia available for the 2025-2026 RSV season, offering a new tool in the fight against this common respiratory illness.
The FDA approved clesrovimab for the prevention of RSV disease in infants. Image: Adobe Stock.
Dr. Octavio Ramilo, chair of infectious diseases at St. Jude’s Children’s Research Hospital and a principal investigator for Merck, emphasized the significance of this approval. “RSV disease is the leading cause of infant hospitalization in the U.S.,” Ramilo said in a press release, noting that enflonsia’s dosing convenience and strong clinical data make it a promising intervention.
The FDA’s decision was supported by a phase 2b/3 trial. Results showed that a single dose of clesrovimab reduced RSV-related lower respiratory infections requiring medical attention by 60.5% over a five-month period, compared to a placebo. Hospitalizations were reduced by 84.3% during the same timeframe.
Enflonsia joins nirsevimab as the second single-dose monoclonal antibody approved in the U.S. for RSV prevention. The CDC recommends nirsevimab for infants younger than 8 months entering their first RSV season, particularly those whose mothers were not vaccinated or had unknown vaccination status. Certain high-risk children aged 8 to 19 months entering their second RSV season are also eligible.
A key difference between the two monoclonal antibodies is that Enflonsia features a fixed dose, nonetheless of the infant’s weight, while nirsevimab’s dosage is weight-based.
Ramilo noted last fall that a single dose of clesrovimab effectively prevented severe RSV disease in high-risk infants, including those born prematurely or with chronic lung or heart conditions. This contrasts with the five doses of palivizumab, another monoclonal antibody, often required for similar protection.
Common side effects associated with clesrovimab, according to the press release, include injection-site redness, swelling, and rash.
The CDC’s Advisory Committee on Immunization Practices is scheduled to discuss and vote on recommendations for clesrovimab at its meeting later this month.
What’s next
With the FDA approval secured, Merck is gearing up to launch Enflonsia for the 2025-2026 RSV season. The CDC’s upcoming vote on recommendations will further shape the landscape of RSV prevention strategies, offering health care providers and parents more options to protect infants from this common and potentially serious virus.