FDA refuses to review Moderna application for mRNA-based flu vaccine

The U.S. Food and Drug Administration (FDA) issued a "refusal-to-file" letter to Moderna on Tuesday, declining to review the company’s application for the first mRNA-based influenza vaccine. The agency cited concerns regarding the design of a 40,000-person clinical trial, stating it did not compare the new shot to the "best-available standard of care" for seniors. FDA vaccine director Dr. Vinay Prasad stated the application lacked an "adequate and well-controlled trial" because it did not use a brand specifically recommended for individuals aged 65 and older as a comparator.

Moderna officials stated that the FDA had previously agreed to the study's design in 2024, though officials at the time expressed a preference for a different comparator for older participants. The company noted it had shared additional data from a separate trial comparing the new vaccine against a licensed high-dose shot used for seniors. Moderna CEO Stephane Bancel said the FDA "did not identify any safety or efficacy concerns" and argued the decision "does not further our shared goal of enhancing America’s leadership in developing innovative medicines."

The company has requested an urgent meeting with the agency and is pursuing approval for the vaccine in Europe, Canada, and Australia. The refusal comes as the FDA moves to tighten federal vaccine approvals, including a shift away from a decades-old practice that allowed manufacturers to update annual flu shots by demonstrating an immune response rather than conducting long-term efficacy studies.