The U.S. Food and Drug Administration declined to file Moderna’s application for its mRNA seasonal influenza vaccine, citing concerns with the trial’s control arm and arguing the comparator did not reflect the "best‑available standard of care," according to company disclosures and a STAT report. Moderna said the agency raised procedural, not safety or efficacy, objections and has requested a meeting to clarify the path forward. Moderna and independent coverage note the dispute centers on trial design choices and comparator selection; the company asserts prior FDA feedback had approved the study design. The letter was signed by CBER leadership; the move follows broader shifts in U.S. vaccine oversight and has prompted scrutiny about changing evidentiary expectations for vaccine pivotal trials.