FDA approves first mRNA flu vaccine for older adults

The Food and Drug Administration on Wednesday approved mFlusiva, the first influenza vaccine using messenger RNA technology, for adults aged 50 to 65 and those 65 and older. The vaccine is manufactured by Moderna.

In a late-stage clinical trial involving more than 40,000 older adults across 11 countries, mFlusiva was found to be about 27% more effective than a standard flu shot. Traditional flu vaccines typically range from 22% to 56% effectiveness, according to the Mayo Clinic.

The FDA granted approval on the condition that Moderna conduct an additional clinical trial in the 65-and-older age group. The agency initially declined to review the application this year, citing a trial design that compared mFlusiva to a standard-dose vaccine rather than the high-dose vaccine recommended by the CDC for older adults, but reversed course a week later.

An independent FDA vaccine advisory committee unanimously recommended approval in June. Side effects such as injection-site pain, fatigue, and headaches were more common with mFlusiva but were generally mild to moderate.

A key advantage of mRNA technology is faster production: Moderna says it takes two to three months from strain selection to vaccine rollout, compared with about six months for traditional egg-based manufacturing. This shorter timeline could allow a closer match to circulating influenza strains each season.

Influenza hospitalizes hundreds of thousands of people in the U.S. annually and causes tens of thousands of deaths, with older adults at higher risk for severe illness.

Despite FDA approval, the vaccine's practical availability is uncertain. The CDC's Advisory Committee on Immunization Practices (ACIP), which typically issues formal recommendations that trigger insurance coverage and federal distribution, has been blocked from convening by a federal judge.

Without ACIP guidance, private insurers are unlikely to cover the shot, and federal programs such as Vaccines for Children and Medicaid will not distribute it. Dr. Ofer Levy of Boston Children's Hospital noted the vaccine can still be legally prescribed, but access would be severely limited. Moderna says mFlusiva will be available for the fall flu season.