For some older adults, the annual flu vaccination now comes with a new option. In August, the US Food and Drug Administration approved mFlusiva, the nation’s first flu vaccine using mRNA technology, for people 50 and older.

Moderna says the vaccine is available at more than 13,000 locations across the United States. Walgreens is offering limited quantities, while CVS is providing the shot upon request in selected areas, with availability varying by location.

The approval followed a difficult regulatory path amid federal funding cuts for mRNA vaccine development. The FDA initially declined Moderna’s request to review the vaccine, but the agency’s independent vaccine advisers unanimously concluded in June that its benefits outweighed its risks.

Traditional flu vaccines use weakened or inactivated viruses, or pieces of the virus, to train the immune system. An mRNA vaccine instead provides instructions that allow the body to make a copy of a viral protein, prompting an immune response.

That manufacturing approach could offer an important timing advantage. Influenza constantly mutates, and scientists must select the strains most likely to dominate during the coming flu season.

Conventional vaccines are manufactured by growing influenza viruses in cells or chicken eggs, requiring strain selection around February. Because mRNA vaccines can be produced more quickly, selection could occur in May, closer to the time when vaccinations begin.

Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said the additional flexibility could help manufacturers more closely match vaccine strains with circulating viruses.

MFlusiva received standard approval for adults ages 50 through 64. For adults 65 and older, the FDA granted accelerated approval after an unusual period of back and forth between the agency and Moderna.

The FDA had questioned Moderna’s study because its control group received a standard dose flu vaccine. CDC guidance recommends enhanced vaccines for adults 65 and older, meaning the comparison did not reflect the preferred standard of care for that age group.

For people 65 and older, Moderna presented evidence that mFlusiva produced more antibodies than an enhanced flu vaccine. The FDA required Moderna to conduct a study during the coming flu season to determine whether that antibody advantage produces a clinical benefit.

In Moderna’s study of more than 40,000 adults older than 50, mFlusiva was about 27% more effective than standard flu shots during the 2024 through 2025 vaccine season. The mRNA vaccine also produced adverse reactions more frequently.

Most reported reactions were mild to moderate and resolved within days. They included injection site pain, muscle and joint pain, nausea, vomiting, fever, headache and chills, while serious adverse events occurred at similarly low rates among recipients of both vaccine types.

People allergic to any vaccine ingredient, or those who previously developed Guillain-Barré syndrome after a flu vaccination, should not receive mFlusiva. Experts said more evidence is still needed to assess its effectiveness among adults 65 and older compared with enhanced vaccines.

Finding the shot may be difficult this season because many pharmacies and clinics placed flu vaccine orders earlier in the year. Moderna recommends using its vaccine finder, while Walgreens and CVS advise customers to contact local pharmacies about supply.

Insurance coverage also drew uncertainty because the CDC’s Advisory Committee on Immunization Practices had not reviewed the vaccine. Moderna said mFlusiva should be covered by most commercial insurance plans and Medicare Part B.

Older adults face especially high risks from influenza. During the 2024 through 2025 season, adults older than 50 represented 76.9% of flu hospitalizations but 34.4% of symptomatic illnesses, while adults older than 65 accounted for 70.6% of deaths and 8.8% of illnesses.

Flu vaccination is intended primarily to reduce severe disease rather than prevent every minor illness. The flu kills an estimated 12,000 to 52,000 Americans annually, depending on the severity of the season.

Doctors generally advise receiving a flu shot before the end of October, although vaccination remains useful throughout flu season. It takes about two weeks for protection to develop, and cases often peak between December and February, sometimes as late as March.