Moderna says the FDA has declined to file its application for an mRNA-based influenza vaccine because the company’s 40,000-person trial did not use the agency’s preferred U.S. standard-of-care comparator, particularly for those 65 and older. Moderna reports the trial showed modest benefit in adults 50+, and the company says the FDA raised no specific safety or efficacy concerns. Moderna has requested an urgent meeting with the FDA and has also filed applications in Europe, Canada and Australia.
FDA Declines to File Moderna’s mRNA Flu Vaccine Application, Citing Trial-Design Concerns
FILE - A sign marks an entrance to a Moderna building in Cambridge, Mass., May 18, 2020. (AP Photo/Bill Sikes, File)(ASSOCIATED PRESS)
Moderna announced Tuesday that the U.S. Food and Drug Administration has refused to file its application for a new influenza vaccine developed with mRNA technology. The agency’s decision centers on how Moderna designed a 40,000-person clinical trial and the choice of comparator vaccine used in the study.
What the FDA Said
In a refusal-to-file letter, FDA vaccine director Dr. Vinay Prasad wrote that the agency does not view the submission as supported by an "adequate and well-controlled trial" because the study did not compare Moderna’s candidate to "the best-available standard of care in the United States at the time of the study." Prasad noted prior 2024 guidance the FDA had given Moderna—guidance the agency says was not followed.
Moderna’s Response
Moderna says FDA officials had previously indicated the standard-dose comparator it selected would be acceptable, while also suggesting that a different brand—one specifically recommended for seniors—would be preferred for participants aged 65 and older. The company adds that the FDA allowed the trial to proceed as originally planned and that it submitted supplemental data from a separate study comparing the investigational vaccine to a licensed high-dose influenza vaccine for seniors.
FILE - The Food and Drug Administration seal is seen at the Hubert Humphrey Building Auditorium in Washington, April 22, 2025. (AP Photo/Jose Luis Magana, File)(ASSOCIATED PRESS)
“The FDA did not identify any safety or efficacy concerns with our product,” Moderna CEO Stephane Bancel said. He also said the agency’s action “does not further our shared goal of enhancing America’s leadership in developing innovative medicines.”
Why This Matters
Moderna reported that the 40,000-person trial showed the mRNA vaccine was modestly more effective than the comparator in adults 50 and older. Refusing to file is an uncommon step for the FDA, especially for a novel vaccine, since approvals typically follow extensive, iterative discussions between companies and agency staff.
Next Steps and Wider Context
Moderna has requested an urgent meeting with the FDA and said it has also filed applications in Europe, Canada and Australia. The decision comes amid broader changes at the FDA under Health Secretary Robert F. Kennedy Jr., including heightened scrutiny of mRNA products, new guidance on COVID-19 vaccines and reductions in certain mRNA vaccine funding. An internal FDA memo last year suggested limiting a streamlined pathway for routine influenza vaccine updates—a stance that prompted public criticism from former FDA commissioners.
Bottom line: The FDA’s refusal to file focuses on trial comparator choices and study design rather than identified safety or efficacy problems, and Moderna is seeking immediate clarification while pursuing regulatory reviews abroad.
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