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FDA Opens Safety Review of Infant RSV Antibody Drugs Beyfortus and Enflonsia

The agency says any label changes will occur only if a full review supports a safety concern.

Signage is seen outside of the Food and Drug Administration (FDA) headquarters in White Oak, Maryland, U.S., August 29, 2020. REUTERS/Andrew Kelly/File Photo
FILE - The U.S. Food and Drug Administration building is seen behind FDA logos at a bus stop on the agency's campus in Silver Spring, Md., Aug. 2, 2018. (AP Photo/Jacquelyn Martin, File)
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Overview

  • Senior executives at Merck, Sanofi, and AstraZeneca were briefed last week to expect additional safety questions on their infant RSV products.
  • The review focuses on Beyfortus and Enflonsia, long-acting monoclonal antibodies recommended for babies entering their first RSV season.
  • Manufacturers and prior studies report no seizure signal, citing more than 50 studies and post‑marketing data covering over 6 million infants.
  • CDC real‑world analyses for the 2024–25 season associated these interventions with up to a 43% reduction in infant RSV hospitalizations.
  • Acting CDER director Tracy Beth Hoeg initiated internal queries in June and has noted a non‑statistically significant mortality imbalance in trials, while it remains unclear whether the FDA will seek label changes or restrict access following the review.