FDA approves first mRNA vaccine for seasonal flu

The U.S. Food and Drug Administration (FDA) has approved a new seasonal flu vaccine that uses mRNA as its base.

Moderna, the vaccine's maker, announced Wednesday (Aug. 5) that a vaccine advisory committee to the FDA unanimously agreed that the shot is safe and effective for preventing illness from seasonal influenza. The shot, called mFlusiva or mRNA-1010, has been approved for people ages 50 and older.

Similar to mRNA vaccines against COVID-19, the vaccine uses the genetic molecule mRNA to encode instructions for cells in the body. In this case, it prompts the cells to build hemagglutinin (HA), a protein found on the surface of influenza viruses. Flu viruses use this protein to infiltrate human cells, and it's the same protein targeted by conventional flu vaccines. Following vaccination with mFlusiva, the immune system learns to recognize the HA protein on targeted flu strains, thereby improving its ability to block the viruses from infecting cells.

The HA protein poses a major challenge for conventional flu vaccines because it mutates very rapidly as the viruses multiply and spread — and these existing vaccines take months to manufacture. That's one reason the resulting shots aren't always a great match for the flu viruses that end up circulating in any given year. A benefit of the mRNA platform is that vaccines can be produced very quickly and thus made to better match the season's dominant strains.

mFlusiva's approval was based in part on a late-stage clinical trial involving over 40,000 people ages 50 and up who were vaccinated for the 2024-2025 Northern Hemisphere flu season. Half received the mRNA-based shot, and half received a standard dose of a conventional flu vaccine (as opposed to the higher-dose option available to older adults in the U.S.).

Of the 40,000 participants, about 970 got sick with flu, including 2% of the mRNA group and 2.8% of the standard group. That means the mRNA vaccine was 26.6% more protective than the conventional vaccine against illness from flu in this trial.

mFlusiva also offered superior protection against each of the three flu subtypes included in the vaccine. And in participants ages 65 and up, the vaccine was 27.4% more protective, overall.

More people in the mRNA group experienced side effects like injection-site pain, headache, fatigue and achiness, compared with the standard group, but these effects were mostly short-lived and mild to moderate in severity. These side effects were consistent with what was seen in earlier trials of the vaccine.

An additional trial involved a group of adults ages 65 and older and directly compared mFlusiva to an existing high-dose flu vaccine, which is approved only for older adults in the U.S. The findings suggested that the mRNA vaccine generated superior immune protection than the conventional option, based on antibody levels.

These results led the FDA advisory committee to decide that the vaccine's benefits outweigh its risks, and the agency ultimately approved it. For adults ages 50 to 64, the vaccine earned standard approval, and for adults 65 and up, it earned "accelerated approval," meaning further trials will be conducted to confirm the benefit of the shot over the high-dose option for this population.

"Flu remains a significant public health challenge, and mFLUSIVA provides an important new option for America's seniors," Moderna CEO Stéphane Bancel said in a statement.

The approval appears to mark a shift in the government's stance on mRNA vaccines.

Under the second Trump administration, the federal government has been broadly retracting its support for mRNA vaccines, directly canceling hundreds of millions of dollars in funds for research and development and indirectly sending a chilling effect through the mRNA field, experts previously told Live Science. Even Moderna has been pulling back from investments, citing opposition from the U.S. market. Health Secretary Robert F. Kennedy Jr. has repeatedly voiced his opposition to mRNA technology.

When Moderna initially filed for mFlusiva's approval in February, the FDA declined to review the application — but then changed its mind one week later. The exact motivation for this reversal was unclear to experts.