Why the FDA Paused Review of Moderna's mRNA Flu Shot

The U.S. Food and Drug Administration issued a refusal-to-file letter for Moderna's seasonal influenza vaccine, mRNA-1010, on February 10, 2026, preventing a formal U.S. review. The refusal centered on Moderna's choice of comparator in its pivotal trial, which the agency said did not reflect the 'best-available standard of care' for older adults, a point that the company disputes.

Moderna's submission included two Phase 3 studies that enrolled a combined 43,808 participants and met their prespecified primary endpoints, with one trial reporting a relative vaccine efficacy of 26.6% against a standard-dose comparator in adults 50 and older. Although the FDA's letter did not identify safety or efficacy concerns, the agency emphasized that the trial design was not 'adequate and well-controlled' because of the comparator issue; the letter was signed by Vinayak Prasad, director of CBER.

Moderna has requested a Type A meeting to seek clarity and has said the vaccine dossier is under review in the European Union, Canada and Australia, where regulators have accepted the filings. The company noted that, subject to those reviews, earliest potential approvals in other countries could arrive in late 2026 or early 2027.

The U.S. Department of Health and Human Services has reduced or canceled nearly $500 million in mRNA vaccine projects under Health Secretary Robert F. Kennedy Jr., a development that has altered funding and regulatory priorities and has been cited by critics as reshaping the environment for respiratory vaccine innovation. Consequently, manufacturers and public health experts are watching whether meetings with FDA will lead to a revised path for U.S. licensure.