It offers hope against RSV.
A new antibody injection called Enflonsia has been approved by the U.S. Food and Drug Administration to help protect infants from respiratory syncytial virus (RSV), a common virus that poses serious risks to babies. Developed by Merck, the single-dose injection is intended to safeguard newborns through their first RSV season, which generally occurs from fall through early spring.
Clinical trials showed that Enflonsia was highly effective, reducing hospitalizations due to RSV by over 84% and lowering the risk of severe respiratory infections by more than 60%. The injection demonstrated a similar safety profile to a placebo, with only minor side effects such as injection site swelling and mild rash. Merck plans to distribute the drug in time for the next RSV season to help ease the burden on families and healthcare systems.
Before it becomes available to the public, Enflonsia must be reviewed and recommended by the Centers for Disease Control and Prevention (CDC). However, that review has been delayed due to recent changes in the CDC’s vaccine advisory panel. Some of the newly appointed members are known for their skepticism about vaccines, which may further impact the timeline for the drug’s rollout.
RSV is extremely common, with most children contracting it by the age of two. While it typically causes mild symptoms in older children and adults, it can be life-threatening for infants, sometimes leading to bronchiolitis or pneumonia. Each year, RSV is responsible for tens of thousands of hospitalizations among young children in the U.S., with infants under six months particularly vulnerable.
Enflonsia adds to a limited but growing set of preventive tools, including Beyfortus (another monoclonal antibody) and vaccines given during pregnancy. A recent CDC report showed that RSV hospitalization rates dropped during the 2024–2025 season, likely due to increased preventative measures. Pediatric experts are hopeful that broader access to treatments like Enflonsia will reduce severe outcomes and ease pressure on hospitals during RSV season.
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