FDA Rejects Moderna’s mRNA Flu Vaccine Application
In a recent announcement, the U.S. Food and Drug Administration (FDA) has decided not to review Moderna’s application for a new flu vaccine that uses mRNA technology. This decision is likely to postpone the vaccine’s release, which was aimed at providing enhanced protection for older adults.
Moderna received a “refusal-to-file” letter from the FDA’s Center for Biologics Evaluation and Research (CBER). The FDA cited concerns over the study design, indicating that it did not meet the criteria of being “adequate and well-controlled.” Specifically, the FDA pointed out that the study did not use a comparison that reflects the best available care.
Stéphane Bancel, Moderna’s CEO, responded by highlighting that the FDA’s decision did not raise any safety or effectiveness concerns about their vaccine. He emphasized the importance of reviewing the submission thoroughly, especially since it was previously discussed and agreed upon with the FDA.
Bancel expressed hope for a productive dialogue with the FDA to clarify the path forward. He noted that it’s crucial for American seniors and those with health issues to have access to new innovations made in the U.S.
Broader Context
This decision comes at a time of increased scrutiny of vaccine approvals, especially under Health Secretary Robert F. Kennedy Jr., who has been critical of mRNA vaccines in the past year. Kennedy has made significant changes, including firing members of the federal vaccine advisory panel and halting several mRNA vaccine contracts.
Currently, the FDA has authorized COVID-19 vaccines for high-risk groups only, and last May, the vaccines were removed from the CDC’s routine immunization schedule for healthy children and pregnant women.
Moderna’s Response
According to Moderna, the refusal was tied to the choice of a standard-dose seasonal flu vaccine as a comparison in the Phase 3 trial—a choice the FDA described as inadequate. Moderna believes this decision contradicts earlier communications from the FDA, which had previously stated that the standard-dose comparator was acceptable, although a higher-dose vaccine was recommended for older participants.
Moderna also mentioned that the FDA had raised no concerns about the trial’s adequacy before its submission or the initiation of the study.
In August 2025, after completing the Phase 3 trial, Moderna held a meeting with CBER, which requested further analyses to support the comparator chosen. The company provided this information but was surprised by the refusal to review the application.
Moderna has requested a meeting with CBER to better understand the basis for the RTF letter and noted that regulatory reviews are still ongoing in other countries, including the European Union, Canada, and Australia.
