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- Posted December 11, 2025
FDA Reviewing RSV Drugs for Infants, Though No Safety Issues Found
Federal regulators have begun a safety review of two RSV medicines used to protect infants, even though no safety problems have been reported.
The review covers Beyfortus (from Sanofi and AstraZeneca) and Enflonsia (from Merck), both monoclonal antibodies that help shield babies from respiratory syncytial virus, or RSV.
The move comes as several immunizations have faced new scrutiny under U.S. Health Secretary Robert F. Kennedy Jr.
The U.S. Food and Drug Administration (FDA) said it is taking a close look at all available data, as it does with any approved product.
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," HHS spokesperson Andrew Nixon said.
Drugmakers say the treatments have strong safety records.
Sanofi told NBC News that Beyfortus has been studied in more than 50 clinical trials involving more than 400,000 infants, with no safety issues identified. The company noted that more than 6 million babies worldwide have received the drug.
Merck also defended Enflonsia’s safety, saying the company welcomes ongoing discussions with the FDA.
A spokesperson for Merck also told NBC News in an email that the bar for establishing the safety of vaccines and preventive therapies like Enflonsia “is exceptionally, and appropriately, high.”
Both products work like vaccines but deliver antibodies directly into the body.
The U.S. Centers for Disease Control and Prevention (CDC) recommends Beyfortus or Enflonsia for babies younger than 8 months entering their first RSV season. For high-risk older infants, only Beyfortus is recommended.
It's unclear whether the FDA’s review will lead to new warnings or restrictions.
“I certainly hope nothing regulatory comes of this, because there’s no basis for it,” Dr. Sean O’Leary of the American Academy of Pediatrics told NBC News.
"But even if it doesn’t, this systematic attempt to dismantle our immunization infrastructure is causing real harm in real time, in creating confusion among parents and even among clinicians," he added.
O’Leary warned that limiting access to RSV protection would “inevitably lead to fewer children receiving the monoclonal antibody and more kids getting hospitalized.”
RSV sends 2% to 3% of infants under 6 months to the hospital each year, according to the CDC.
While many infections cause cold-like symptoms, RSV can also trigger pneumonia or bronchiolitis, which makes breathing difficult.
“These products have been shown to be very safe in clinical trials,” O’Leary said. “Now that they’ve been put into broad use, we’re seeing really profound impacts on hospitalizations for young children.”
More information
The Mayo Clinic has more on RSV.
SOURCE: NBC News, Dec. 9, 2025
