FDA Approves First mRNA Flu Vaccine, Moderna's mFLUSIVA

FDA approved mFLUSIVA on 5 August 2026, licensing Moderna's mRNA-1010 as the first seasonal influenza vaccine built on messenger RNA technology to reach the U.S. market. The approval is split by age — standard approval for adults 50 to 64, accelerated approval for adults 65 and older — and arrives six months after FDA initially refused to even review the application, a dispute the agency reversed inside two weeks.

An approval split by age, not just by dose

Moderna structured its own regulatory pathway around age rather than seeking one blanket approval. Adults 50 to 64 fall under a standard approval, supported by a Phase 3 trial of roughly 41,000 participants that measured mFLUSIVA against a licensed standard-dose comparator and found about 26.6% relative vaccine efficacy, with a 95% confidence interval of 16.7% to 35.4%. Adults 65 and older — the group flu vaccines exist mainly to protect — instead cleared the bar through accelerated approval, built on an immunogenicity trial of 2,992 participants compared against a licensed high-dose vaccine rather than a clinical-efficacy endpoint. That track carries a condition: Moderna must run a postmarketing trial confirming clinical benefit in older adults, and FDA can withdraw the accelerated approval for that population if the confirmatory data disappoints.

The refusal-to-file, reversed

The approval follows a review dispute unusual enough to draw its own coverage. On 10 February 2026, CBER, under Director Vinay Prasad, issued Moderna a refusal-to-file letter — a determination that an application is too incomplete to review at all, rather than a rejection on the merits. The stated reason was narrow: the Phase 3 trial's comparator, a licensed standard-dose seasonal flu vaccine, did not in CBER's view reflect the “best-available standard of care.” Moderna disputed this on the record, noting that neither FDA's regulation on adequate and well-controlled studies nor its guidance for industry on seasonal influenza vaccines references a “best-available standard of care” test for comparator selection, and that the letter contradicted prior written communications in which CBER had told the company a standard-dose comparator would be acceptable. Eight days later, following a high-priority Type A meeting, CBER told Moderna the application would proceed to review after all, assigning the August 5 PDUFA goal date that the approval has now met.

What comes next

Moderna says it expects mFLUSIVA to be available for the 2026-2027 flu season. For the 50-64 population, the approval is final and unconditional. For adults 65 and older — the segment carrying the greatest burden of severe flu illness, and the one every seasonal vaccine ultimately has to answer for — the license remains provisional on a confirmatory trial FDA has not yet seen. The refusal-to-file dispute leaves its own residue: a public disagreement between a sponsor and CBER's director over what “best-available standard of care” requires of a comparator arm, unresolved by regulation or guidance, that other mRNA vaccine sponsors will now have to read closely before designing their own trials.