FDA approves first mRNA vaccine for seasonal flu

The U.S. Food and Drug Administration has approved mFlusiva, an mRNA-based seasonal influenza vaccine developed by Moderna, for use in adults ages 50 and older. The decision follows a unanimous recommendation by an FDA vaccine advisory committee that the shot is safe and effective. Like mRNA vaccines for COVID-19, mFlusiva delivers genetic instructions for cells to produce hemagglutinin, a surface protein the flu virus uses to enter human cells, training the immune system to recognize and block the virus.

A key advantage of the mRNA platform is rapid production, which allows the vaccine to be updated more quickly to match circulating flu strains. Conventional flu vaccines take months to manufacture, often resulting in a mismatch with the dominant viruses of the season.

The approval was based in part on a late-stage trial involving more than 40,000 participants ages 50 and up during the 2024-2025 Northern Hemisphere flu season. Half received mFlusiva and half received a standard-dose conventional flu vaccine. About 970 participants contracted flu: 2% in the mRNA group versus 2.8% in the standard group, making mFlusiva 26.6% more protective against flu illness overall. Superior protection was seen across all three flu subtypes in the vaccine.

In participants 65 and older, the mRNA vaccine was 27.4% more protective than the standard-dose comparator. A separate trial in adults 65 and up compared mFlusiva directly with an existing high-dose flu vaccine approved for that age group; results suggested the mRNA vaccine generated superior immune protection based on antibody levels.

More recipients of mFlusiva reported side effects such as injection-site pain, headache, fatigue and achiness compared with the standard vaccine group, but these were mostly short-lived and mild to moderate in severity, consistent with earlier trials.

For adults 50 to 64, the vaccine received standard approval. For those 65 and older, it received accelerated approval, meaning further trials will be conducted to confirm its benefit over the high-dose option for that population.

The approval marks a shift after the FDA initially declined to review Moderna's application in February before reversing course a week later. The decision comes amid a broader federal pullback on mRNA vaccine funding and public opposition from Health Secretary Robert F. Kennedy Jr., though the advisory committee concluded the vaccine's benefits outweigh its risks.

Moderna CEO Stéphane Bancel said the vaccine provides an important new option for America's seniors, as flu remains a significant public health challenge.