U.S. regulators have begun a new round of safety questioning around the RSV antibody products given to infants, notifying executives at Merck, Sanofi, and AstraZeneca that their approved treatments will be reassessed. The move comes under the direction of Health Secretary Robert F. Kennedy Jr., who has long voiced doubts about childhood immunization programs and argues that many medical products have not been fully evaluated for potential risks.
The therapies under renewed scrutiny include Sanofi and AstraZeneca’s Beyfortus, along with Merck’s newer product, Enflonsia. These medications differ from traditional vaccines because they supply infants with lab-made antibodies that offer protection during their most vulnerable months, typically from birth through the first year of life. They are currently part of the CDC’s recommended schedule for children.
According to individuals familiar with internal discussions, questions surrounding these products began circulating within the FDA over the summer. Tracy Beth Hoeg, a senior adviser within the agency who has previously challenged aspects of U.S. vaccine policy, reportedly raised early concerns. Internal files show that George Tidmarsh, who at the time led the FDA division overseeing RSV products, directed staff in August to take a second look at data supporting Enflonsia’s approval.
Last week, officials from the FDA’s Center for Drug Evaluation and Research held a short call with representatives from all three pharmaceutical companies, explaining that additional safety information may soon be requested. So far, the FDA has not indicated whether product labels might change or whether distribution could be restricted.
A spokesperson for the Department of Health and Human Services said the agency would continue evaluating all available safety information and that any action taken would be based on scientific evidence and patient welfare.
Sanofi responded by emphasizing that Beyfortus has been extensively studied in more than 50 trials and used by more than 400,000 infants worldwide. Merck also acknowledged the meeting with regulators and stated it remains confident in the safety of Enflonsia.
RSV remains one of the leading causes of hospitalization for young infants. Federal data suggests that every year, two to three out of every 100 babies under six months require hospital care due to the virus, and high-risk infants may face life-threatening complications such as pneumonia.
Early commercial performance reflects the strong demand for these products: Beyfortus generated over $2.6 billion globally in 2024, while Enflonsia is projected to earn around $250 million next year.
Despite this, the RSV therapies have become the latest topic of debate among skeptics of childhood immunization. Journalist Maryanne Demasi recently suggested that the products might be linked to seizures—claims contradicted by multiple safety studies. Infectious-disease specialists, including Stanford University’s Jake Scott, argue that Demasi’s analysis combines data from infants of different ages who receive separate vaccine schedules, which could distort findings.
Another point of contention emerged when Dr. Robert Malone, a Kennedy-appointed member of a national vaccine advisory panel, publicly walked back his earlier recommendation supporting widespread Enflonsia use.
Hoeg also highlighted trial data showing a small difference in death rates between treatment groups and their control groups. Experts note that this difference was not statistically significant and could have occurred by chance, but she suggested that the advisory committee may revisit the issue.
The FDA’s reassessment reflects a wider national conversation about how children’s medical products should be evaluated and monitored. For now, health officials emphasize that RSV antibody treatments remain an important tool in preventing dangerous respiratory infections during infancy, even as further review continues.
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