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The U.S. Food and Drug Administration (FDA) refused to consider Moderna’s application for a new flu vaccine using mRNA technology, the company announced Tuesday, a decision that could delay the introduction of a shot designed to offer stronger protection for older adults.
Moderna said it received what’s known as a “refusal-to-file” (RTF) letter from the FDA’s Center for Biologics Evaluation and Research (CBER), citing the lack of an “adequate and well-controlled” study with a comparator arm that “does not reflect the best-available standard of care.”
Stéphane Bancel, chief executive officer of Moderna, said the FDA’s decision did not “identify any safety or efficacy concerns with our product” and “does not further our shared goal of enhancing America’s leadership in developing innovative medicines.”
“It should not be controversial to conduct a comprehensive review of a flu vaccine submission that uses an FDA-approved vaccine as a comparator in a study that was discussed and agreed on with CBER prior to starting,” Bancel said in a statement. “We look forward to engaging with CBER to understand the path forward as quickly as possible so that America’s seniors, and those with underlying conditions, continue to have access to American-made innovations.”
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The FDA refused to review Moderna’s application for a new mRNA-based flu vaccine, citing concerns about the design of its late-stage clinical trial. (iStock)
The rare decision from the FDA comes amid increased scrutiny over vaccine approvals under Health Secretary Robert F. Kennedy Jr., who has criticized mRNA vaccines and rolled back certain COVID-19 shot recommendations over the past year.
Kennedy previously removed members of the federal government’s vaccine advisory panel and appointed new members, and moved to cancel $500 million in mRNA vaccine contracts.
The FDA authorized COVID-19 vaccines for the fall for high-risk groups only. Last May, Kennedy announced the vaccines would be removed from the CDC’s routine immunization schedule for healthy children and pregnant women.
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The FDA’s refusal to review Moderna’s mRNA flu vaccine comes amid broader vaccine policy shifts under Health Secretary Robert F. Kennedy Jr. (Jason Mendez/Getty Images)
According to Moderna, the refusal-to-file decision was based on the company’s choice of comparator in its Phase 3 trial — a licensed standard-dose seasonal flu vaccine — which the FDA said did not reflect the “best-available standard of care.”
Moderna said the decision contradicts prior written communications from the FDA, including 2024 guidance stating a standard-dose comparator would be acceptable, though a higher-dose vaccine was recommended for participants over 65.
Moderna said the FDA “did not raise any objections or clinical hold comments about the adequacy of the Phase 3 trial after the submission of the protocol in April 2024 or at any time before the initiation of the study in September 2024.”
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Moderna said it received a “refusal-to-file” letter from the FDA for its new mRNA flu vaccine, a move that could delay the shot’s rollout. (iStock)
In August 2025, following completion of the Phase 3 efficacy trial, Moderna said it held a pre-submission meeting with CBER, which requested that supportive analyses on the comparator be included in the submission and indicated the data would be a “significant issue during review of your BLA.”
Moderna said it provided the additional analyses requested by CBER in its submission, noting that “at no time in the pre-submission written feedback or meeting did CBER indicate that it would refuse to review the file.”
The company requested a Type A meeting with CBER to understand the basis for the RTF letter, adding that regulatory reviews are continuing in the European Union, Canada and Australia.
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has reached out to the Department of Health and Human Services for comment.
Digital’s Alex Miller and The Associated Press contributed to this report.
