Why did the FDA reverse its decision on Moderna's flu shot?

Agency and company reach agreement after dispute

After an initial refusal to accept Moderna’s application for its mRNA influenza vaccine, U.S. regulators changed course and agreed to review the submission following further discussions with the company. The FDA’s earlier refusal rested on concerns about the design of Moderna’s pivotal trial—specifically whether the comparator vaccine used in the study represented the best standard of care. Moderna and the agency engaged in follow-up talks that led to the agency deciding the application would be considered.

What is known about the implications

• The reversal means Moderna’s vaccine will enter the formal review process, which could lead to an approval decision if data meet the FDA’s standards for safety and effectiveness.
• The episode has provoked debate within the agency and the industry about regulatory standards and how trials are judged against existing vaccines.
• The controversy has also raised wider questions about policy direction at the FDA and its relationship with vaccine developers.

What remains unresolved

It is not yet clear how long the review will take or whether additional data requests will be issued. The review process will assess the trial evidence on how well the mRNA flu candidate prevents influenza compared with standard options, and whether its safety profile is acceptable. The decision to review rather than reject outright preserves a pathway for a novel mRNA flu approach to reach the market, while keeping open regulatory scrutiny of trial design and comparators.