Published by Global Banking and Finance Review
Posted on December 9, 2025
6 min readLast updated: January 20, 2026
The FDA is reviewing the safety of RSV therapies for infants, including Beyfortus and Enflonsia, following concerns from vaccine skeptics.
By Dan Levine and Patrick Wingrove
Dec 9 (Reuters) - U.S. health regulators informed senior executives at Merck, Sanofi and AstraZeneca last week that their approved protective RSV treatments for infants would be subject to fresh safety scrutiny following concerns raised by vaccine skeptics, multiple sources familiar with the situation told Reuters.
The preventive therapies - Beyfortus from Sanofi and AstraZeneca and Enflonsia from Merck - would be the latest called into question under U.S. Health Secretary Robert F. Kennedy Jr., a long-time promoter of anti-vaccine views who is presiding over a review of routine childhood immunizations.
Kennedy maintains that the potential risks of such pharmaceutical products have not been properly studied. Leading medical societies and many state health officials say Kennedy is trying to dismantle a vaccine program that prevents disease and saves lives based on his beliefs rather than scientific evidence.
FDA officials appointed under Kennedy began making inquiries into the respiratory syncytial virus therapies over the summer, according to sources and internal documents.
Senior FDA adviser Tracy Beth Hoeg began safety questions internally at the agency as early as June, Health and Human Services Department spokesman Andrew Nixon told Reuters. Hoeg had opposed U.S. health policies during the COVID-19 pandemic and has questioned the use of some childhood vaccines.
Maryanne Demasi, an independent journalist based in Australia who has been critical of COVID vaccines, wrote in an August 17 blog post that the RSV therapies could increase the risk of seizures.
Several safety studies have found no such evidence of seizure risk.
George Tidmarsh, at the time director of the FDA division that oversees the RSV therapies, directed staff in late August to compile information about Enflonsia to take a second look at the agency’s approval of the therapy earlier this year, internal documents reviewed by Reuters show. Beyfortus has been on the U.S. market since July 2023.
Hoeg’s questions within FDA led officials at the agency’s Center for Drug Evaluation and Research to convene a call with the three drug companies last Wednesday to tell them to expect further safety questions from the commissioner’s office, sources familiar with the situation said.
The call was brief, and did not spell out what data might be requested, they said. Hoeg has since been named the acting director of CDER.
It is unclear whether the FDA will ultimately take any actions to change the product label or restrict availability of the therapies. The call with the company executives underscored the seriousness of the inquiry, the sources said.
“FDA routinely evaluates emerging safety information and will update product labeling if warranted by the totality of the evidence," Nixon said in a statement. The agency is "rigorously reviewing the available data, as it does for all products, to ensure decisions remain rooted in evidence-based science and in the best interest of patients," he said.
In a statement Sanofi said the safety and effectiveness of Beyfortus has been demonstrated in over 50 studies involving more than 400,000 infants. Representatives for Merck and AstraZeneca did not immediately respond to requests for comment.
REDUCING RISK FOR INFANTS
Two or three out of every 100 infants under 6 months old are hospitalized with RSV every year, according to federal estimates. For babies at high risk, RSV infection can lead to severe breathing problems and pneumonia and may become life-threatening.
Unlike vaccines, these RSV therapies do not stimulate the immune system to create its own antibodies. Instead, they provide infants with ready-made antibodies to protect against illness in their first six months to over one year of life.
Beyfortus generated combined global sales of more than $2.6 billion in 2024. Merck’s newer Enflonsia is expected to make $250 million in sales next year.
The therapies are included in the U.S. Centers for Disease Control and Prevention’s recommended childhood immunization schedule.
A CDC study of real-world data on Beyfortus and a maternal vaccine showed up to a 43% reduction in RSV hospitalizations for infants during the 2024-25 respiratory illness season, compared to the 2018-2020 periods.
Demasi criticized the CDC's analysis of Beyfortus for considering newborns separately from slightly older babies. She argued in her post that when data on both groups were combined, there appeared to be a statistically significant risk of seizure.
Some scientists have pushed back against the critique. Jake Scott, an infectious-disease physician and Stanford University associate professor, wrote in August that older babies receive multiple vaccines at the same time as the RSV therapy, while newborns typically do not.
Analyzing the age groups separately prevents mis-attributing seizures from other vaccines to the antibody, he wrote.
“Rolling back RSV availability based on baseless concerns would do harm to American children,” Scott wrote on Quillette, an online publication. “Perhaps more importantly, it would set a dangerous precedent in regard to how America’s scientific advisory-committee system might be undermined — or even co-opted— by peddlers of junk science.”
HHS spokesman Nixon said Scott’s concerns “are not baseless,” adding that FDA “must evaluate all evidence through comprehensive reviews.”
Three days after Demasi's post, Dr. Robert Malone, a member of the national vaccine advisory board appointed by Kennedy, said he regretted recommending widespread use of Enflonsia at a June meeting of the committee based on CDC staff analysis.
“I voted in favor of the resolution based on the information and logic presented,” Malone wrote on Substack. “That trust in the data presented now appears to have been ill-advised.”
Malone and other vaccine advisers on Friday scrapped a long-standing recommendation that all American newborns receive the hepatitis B shot, the most consequential change to date in Kennedy’s remaking of U.S. vaccine policy.
At that same meeting, Hoeg cited data from four late-stage clinical trials involving both RSV therapies that she said showed an “unfavorable imbalance” in mortality, with more deaths in the treatment arm than the control.
While not statistically significant, meaning the finding could be due to chance, Hoeg said the issue “could be revisited” by the committee.
(Reporting by Dan Levine in San Francisco and Patrick Wingrove in New York; Editing by Michele Gershberg and Bill Berkrot)
Respiratory Syncytial Virus (RSV) is a common virus that causes respiratory infections, particularly in infants and young children. It can lead to severe respiratory issues and is a significant cause of hospitalizations in this age group.
Vaccines are biological preparations that provide immunity to a particular infectious disease. They stimulate the body's immune system to recognize and fight pathogens without causing the disease.
Safety studies are research investigations conducted to assess the safety and potential side effects of a drug or therapy, ensuring that it is safe for public use before approval.
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