The FDA issued a refusal-to-file for Moderna’s mRNA influenza vaccine, prompting an immediate public dispute between the company and regulators. Moderna said the agency’s letter cited procedural concerns inconsistent with prior guidance and did not identify safety or efficacy deficiencies. The refusal has reverberated across vaccine developers that relied on established pre-submission interactions with the agency. Moderna responded that earlier FDA discussions had approved its comparator choice and that the RTF caught the company by surprise. The move also highlighted a regulatory bottleneck: senior FDA leadership personally signed the letter, signaling a tougher review stance for complex vaccine programs. The company has already pared R&D spending and reorganized its pipeline away from large late-stage respiratory programs. Moderna’s strategic pivot — shifting resources toward oncology and select vaccine targets — reflects immediate operational impacts from the regulatory setback and raises questions about future investment in U.S.-based respiratory vaccine trials.