The U.S. Food and Drug Administration has declined to review Moderna’s application for a novel mRNA-based flu vaccine. Moderna disclosed this decision following receipt of a refusal-to-file letter from the agency.
Reasons for the Rejection
The FDA cited issues with the clinical trial design in a 40,000-participant study. This trial compared the new vaccine to a standard flu shot and demonstrated superior effectiveness in adults aged 50 and older. However, FDA vaccine director Dr. Vinay Prasad stated that the application lacks an adequate and well-controlled trial, as it failed to use the best-available standard of care in the U.S. at the time.
Prasad’s letter referenced prior 2024 guidance from FDA officials, which Moderna did not fully implement. That advice indicated a preference for a high-dose flu shot recommended for seniors aged 65 and older, though Moderna proceeded with its original plan after agency approval.
Moderna’s Position
Moderna maintains that the FDA previously endorsed the chosen comparator vaccine. The company also submitted data from a separate trial against a licensed high-dose senior vaccine. Moderna CEO Stephane Bancel stated, “The FDA did not identify any safety or efficacy concerns with our product.”
The company has requested an urgent meeting with the FDA and pursued approvals in Europe, Canada, and Australia.
Broader Regulatory Context
This refusal marks a rare step for the FDA, especially for innovative vaccines developed through extensive pre-submission discussions. Recent actions under Health Secretary Robert F. Kennedy Jr. include adjustments to COVID-19 vaccine recommendations, added warnings on leading mRNA COVID vaccines, and removal of certain FDA advisory panel members.
Kennedy’s department previously canceled over $500 million in mRNA vaccine development funding. Additionally, the FDA has ended streamlined approvals for annual flu shot updates based on immune response data alone, prompting criticism from more than a dozen former FDA commissioners.
