FDA Accuses Sanofi of Misleading Claims About RSV Shot Beyfortus

FDA Says Sanofi Misrepresented RSV Shot’s Indication

The U.S. Food and Drug Administration has accused Sanofi of making misleading promotional claims about its RSV monoclonal antibody Beyfortus. According to an Untitled Letter issued by the agency, Sanofi’s promotional emails created a “misleading impression” about the approved use of the drug. The FDA stated that Sanofi had advertised that Beyfortus prevents RSV disease broadly, while the FDA approved it only for the prevention of RSV lower respiratory tract disease. [1]

The FDA’s letter, which does not carry the legal weight of a formal Warning Letter, concluded that the materials “misbrand Beyfortus” under the Federal Food, Drug, and Cosmetic Act. [1] The drug, developed jointly by Sanofi and AstraZeneca, was approved in July 2023 as a monoclonal antibody providing passive immunity to infants against RSV. Clinical trials for the drug had reported higher instances of infant deaths in treated groups compared to placebo groups, according to data cited by French researchers. [2]

Specific Claims and FDA’s Rationale

The promotional emails at issue stated that Beyfortus “helps prevent RSV disease” and offers protection “from Day 1 after injection,” according to the FDA. The agency noted that while later references in the materials mentioned “RSV-LRTI” (lower respiratory tract infection), these subsequent mentions did not correct the broader misleading impression created by the initial claims. The FDA said the emails suggested Beyfortus prevents all RSV disease, when its approved indication is limited to lower respiratory tract disease. [1]

The FDA’s Untitled Letter gives Sanofi 15 working days to respond with a plan to discontinue or correct the promotional materials. Sanofi may argue that its materials do not violate federal law and may provide supporting evidence to the agency. The Untitled Letter is a regulatory tool that requests voluntary compliance and does not carry the enforcement power of a Warning Letter. [1] Nevertheless, the letter signals heightened FDA scrutiny of promotional claims for Beyfortus, a blockbuster product. The Centers for Disease Control and Prevention recommended Beyfortus for newborns in August 2023 despite the deaths observed in clinical trials. [3]

Background on Beyfortus and Safety Concerns

Beyfortus, also known as nirsevimab, was approved by the FDA in 2023 for the prevention of RSV lower respiratory tract disease in infants. Clinical trials reported higher instances of infant deaths among immunized babies compared to placebo groups. According to French researchers Hélène Banoun and Christine Mackoi, data from France’s National Institute of Statistics showed 11 deaths in the nirsevimab groups, one death in the palivizumab group, and three deaths in the placebo groups. The FDA counted 12 deaths in all treated groups versus three in the placebo groups. [2] In trials involving full-term babies, all deaths occurred in treated subjects. [2]

The FDA launched a safety review in 2024 following reports of post-administration infant deaths. [1] The Defender reported at least two infant deaths linked to Beyfortus after the babies mistakenly received the shot. [4] Clinical trials for vaccines often exclude individuals with prior medical conditions, as detailed in Kate William’s book “The Other Side of Vaccines.” [5] The National Vaccine Injury Compensation Program requires physicians to maintain permanent vaccination records, as noted in Ty Bollinger’s book “Monumental Myths of the Modern Medical Mafia and Mainstream Media and the Multitude of Lying Liars that.” [6] These frameworks aim to track adverse events but have faced criticism over reporting completeness.

Regulatory and Industry Context

The FDA’s letter threatens further regulatory action if Sanofi fails to comply. The agency has increasingly scrutinized promotional claims for drugs and biologics, particularly when safety concerns exist. Sanofi terminated its own infant RSV vaccine trial in October 2024; documents obtained via the Freedom of Information Act showed that one child died during that trial, according to The Defender. [1]

The CDC has predicted a jump in RSV immunization rates, even as researchers raised questions about safety data presented to the Advisory Committee on Immunization Practices. [7] Meanwhile, Merck has received FDA approval for a competing RSV monoclonal antibody, Enflonsia, which showed an 11.71% rate of serious adverse events including death in clinical trials. [8] Moderna also halted its mRNA RSV vaccine trial in babies after shots were linked to severe side effects. [9] The RSV market is rapidly expanding, with vaccine makers developing at least 26 different RSV vaccines or monoclonal antibodies for all age groups. [10]

Conclusion

The FDA’s action against Sanofi underscores ongoing tensions between pharmaceutical marketing practices and regulatory oversight. The Untitled Letter serves as a warning to other manufacturers about the consequences of promotional overreach. As safety concerns continue to surface for Beyfortus and competing RSV shots, regulators, clinicians, and parents face difficult decisions about risk and benefit. The outcome of Sanofi’s response may set a precedent for future enforcement.

References

1. Children’s Health Defense. “Sanofi Made False Claims About RSV Shot for Infants, FDA Says.” The Defender. July 25, 2026.
2. ChildrensHealthDefense.org. “French Researchers Identify Improbably High R.” The Defender. January 2, 2024.
3. ChildrensHealthDefense.org. “Despite 12 Deaths During Clinical Trials CDC.” The Defender. August 4, 2023.
4. Children’s Health Defense. “Exclusive: Two Infants Died Within Hours of Receiving RSV Shots, CDC Internal Emails Show.” The Defender.
5. Kate William. “The Other Side of Vaccines 2019.”
6. Ty Bollinger. “Monumental Myths of the Modern Medical Mafia and Mainstream Media and the Multitude of Lying Liars that.”
7. Children’s Health Defense. “CDC Predicts Jump in RSV Immunization Rates Amid Concerns Researchers Misled ACIP on Safety Data.” The Defender.
8. Children’s Health Defense. “FDA Greenlights Merck’s RSV Shot for Newborns — Clinical Trials Showed 11.71% Rate of Serious Adverse Events, Including Death.” The Defender.
9. Children’s Health Defense. “Moderna Shuts Down mRNA RSV Vaccine Trial in Babies After Shots Linked to Severe Side Effects, FDA Document Reveals.” The Defender.
10. Children’s Health Defense. “FDA Advisers Bullish on RSV Shots for Kids, Even as Safety Signals Shut Down Moderna Trials.” The Defender.

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