The FDA approved Moderna’s mFlusiva for adults ages 50 and older, making it the first mRNA-based seasonal flu vaccine approved in the U.S.
In a Phase 3 trial of more than 40,000 adults, the vaccine reduced the risk of confirmed influenza-like illness by 26.6% compared with a standard-dose flu vaccine.
Adults 65 and older received accelerated approval, meaning Moderna must conduct additional research to confirm the vaccine’s clinical benefit in this age group.
The FDA has approved Moderna’s mFlusiva, also known as mRNA-1010, for preventing influenza caused by the virus strains included in the vaccine. The approval covers adults ages 50 and older, although the FDA used two different approval pathways depending on age.
Adults ages 50 to 64 received traditional approval based on clinical efficacy data. For adults 65 and older, the vaccine received accelerated approval based largely on immune-response data, along with supporting efficacy findings. That means additional research will be required to confirm its clinical benefit in this older population.
"The FDA approval of mFLUSIVA, our fourth approved product in the United States and the first mRNA-based flu vaccine, demonstrates the continued strength and versatility of our mRNA platform," Stéphane Bancel, Chief Executive Officer of Moderna, said in a news release.
"Flu remains a significant public health challenge, and mFLUSIVA provides an important new option for America's seniors. This approval also reflects the ongoing potential of our mRNA platform to help address important public health challenges through continued scientific innovation. We are grateful to the clinical trial participants, investigators, regulators, and Moderna teams whose contributions made this milestone possible."
How researchers tested it
The main Phase 3 study included 40,805 adults at 301 sites across 11 countries. Participants were randomly assigned to receive either a single injection of mRNA-1010 or a standard-dose flu vaccine. Researchers followed them through the influenza season, for roughly six to eight months.
Researchers looked specifically for influenza-like illness confirmed by RT-PCR testing. During the 2024-2025 Northern Hemisphere flu season, 968 cases were recorded — more than the 836 cases researchers had expected to need for the study. That allowed the primary analysis to be completed after one flu season.
For adults 65 and older, another Phase 3 study compared mRNA-1010 with Fluzone High-Dose and measured antibody responses to four influenza strains.
What the results mean
Among adults 50 and older, mFlusiva had a relative vaccine efficacy of 26.6% compared with the standard-dose vaccine. In other words, people receiving mFlusiva had a lower risk of the specific influenza-like illness measured in the study than those receiving the comparison vaccine.
The FDA also found that mFlusiva produced stronger immune responses than Fluzone High-Dose against all four vaccine-matched strains in adults 65 and older. However, the agency noted remaining uncertainty around protection against one strain, B/Victoria, and how the vaccine will perform across different flu seasons.
The vaccine's side effects were generally mild to moderate and lasted a median of two days, although reactions were reported more often than with the comparison vaccines. The FDA found no safety concerns in an integrated safety population of 35,965 adults ages 50 and older.
For people 65 and older, the story isn't quite finished: Moderna is required to conduct a large Phase 4 study designed to verify the vaccine's clinical benefit under real-world conditions.