The vaccine, called mFlusiva, received full approval for adults ages 50 to 64 and accelerated approval for adults 65 and older (allowing people in this age group to get the vaccine while the company that makes mFlusiva, Moderna, completes an additional study to confirm its clinical benefit in this age group).
“This is really significant,” says Paul Pottinger, MD, director of the Infectious Diseases and Tropical Medicine Clinic at UW Medical Center in Seattle, and cohost of the travel health podcast Germ & Worm. “It gives us not only a new choice, but also a more nimble, responsive way to help prevent flu,” he says.
Moderna is studying mFlusiva in younger age groups, but more data are needed before the FDA could expand its approval, says Dr. Pottinger.
“Since older people don’t typically respond as well to traditional flu vaccines, the idea here was to develop a shot that works better in people over 50,” says David Wohl, MD, a professor of medicine at UNC Chapel Hill in North Carolina and an infectious disease expert. Younger adults produced even stronger immune responses in earlier research, although they also had more short-term side effects after the shot, he says.
Why an mRNA Flu Vaccine Is a Big Deal
Flu vaccines have to be updated every year because influenza viruses are constantly changing. Most traditional flu vaccines are grown in chicken eggs, a process that can take six months or longer, so scientists have to choose which strains to target long before flu season begins, says Pottinger. Those decisions are informed in part by which flu viruses circulate earlier in the year in the southern hemisphere.
mRNA vaccines are made differently. mFlusiva uses lab-made messenger RNA that gives the body’s cells instructions for producing proteins found on the surface of the targeted flu viruses. The immune system learns to recognize those proteins, so the body is prepared to respond if it encounters the viruses later.
One advantage of that approach is speed. Moderna says mFlusiva can go from strain selection to production in about two to three months, compared with roughly six months for traditional flu vaccines, says Pottinger.
“Sometimes that means we have a mismatch between what’s actually coming in the fall and what we made in the spring,” he says. With mRNA technology, vaccine makers can select strains closer to flu season, reducing the window in which the virus can change before people are vaccinated.
mFlusiva Was More Effective Than a Standard Flu Shot in Clinical Trials
The FDA’s decision for adults ages 50 to 64 was based on a late-stage trial of more than 40,000 adults in 11 countries. In the trial, mFlusiva was about 27 percent more effective than a standard-dose flu vaccine at preventing laboratory-confirmed influenza in adults 50 and older.
For people 65 and older, accelerated approval was based largely on a separate study of nearly 3,000 adults that found mFlusiva generated a strong immune response compared with a high-dose flu vaccine.
No new safety concerns were identified. Common reactions included injection-site pain, fatigue, headache, muscle and joint pain, chills, nausea, and fever.
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