The FDA has refused to begin formal review of Moderna’s mRNA influenza vaccine application, citing deficiencies in the pivotal trial’s control arm and trial design. The decision was signed by Vinay Prasad, director of the agency’s biologics office, and prompted immediate public rebuttal from Moderna that the action contradicts prior agency guidance. Moderna said the agency raised no safety or efficacy concerns but concluded the trial did not meet the FDA’s "adequate and well-controlled" standard. The refusal-to-file has ripple effects across regulators and markets: Moderna has requested a Type A meeting to clarify next steps and said the filing is under review in the EU, Canada and Australia. The move prompted a sharp sell-off in Moderna shares and reopened industry debate over comparator choice and shifting regulatory expectations for next-generation vaccine trials. Observers and industry leaders are watching whether the FDA will require new comparator trials or narrower target populations, which could delay market entry and combination vaccine plans.