The FDA has refused to start a review of Moderna’s application for its standalone mRNA influenza vaccine, citing flaws in the pivotal trial’s control-arm design rather than explicit safety or efficacy defects. Moderna said the agency’s letter, signed by CBER head Vinay Prasad, contradicts prior feedback and requested a meeting to clarify the path forward. Moderna reported positive phase III results for mRNA-1010 and said the decision will not alter its 2026 guidance. The dispute centers on whether the trial’s comparator — a licensed standard-dose seasonal flu vaccine — met the regulator’s expectation for an “adequate and well-controlled” study. Companies and investors are watching closely: the ruling could reshape expectations for respiratory vaccine trial design and for combinations that pair flu with COVID-19 vaccines.