The FDA issued a refusal-to-file letter for Moderna’s mRNA influenza vaccine application, halting regulatory review. The letter was signed by Vinay Prasad, director of the agency’s office overseeing vaccines, and Moderna said the decision did not cite safety or efficacy concerns and contradicted prior agency guidance. Moderna has requested a Type A meeting to clarify next steps. Moderna told investors the agency raised issues with its trial comparator and supporting analyses; company executives said the move was inconsistent with pre‑trial and pre‑submission interactions. FDA leadership has defended the decision internally, noting concerns about trial design and comparator choice. The episode has prompted immediate industry debate over regulatory consistency for next‑generation vaccines and may affect developer willingness to pursue large, U.S.-based influenza programs.