RESOLVING THE LEDGER
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On Aug. 5, the U.S. Food and Drug Administration (FDA) approved the first mRNA-based vaccine for influenza. Health experts say the shot, made by Moderna, could have several advantages over traditional flu vaccines, but its approval comes at a time when federal health agencies have walked back recommending flu vaccines for many people.
In a study published in May 2026 in the New England Journal of Medicine that Moderna submitted to the FDA, the mRNA-based flu shot, called mFlusiva, was up to 27% more effective in preventing flu than any of four currently available flu shots. Among more than 40,000 people over age 50 who were randomly assigned to receive either mFlusiva or one of four existing flu shots, those who received a single dose of the mRNA flu vaccine were on average 27% less likely to have lab-confirmed influenza-like illness than those getting another type of flu shot.
“I think this is a historic event and incredibly exciting, both scientifically and from a public-health standpoint,” says Dr. Jeanne Marrazzo, CEO of the Infectious Diseases Society of America.
“Flu remains a significant public health challenge, and mFlusiva provides an important new option for America’s seniors,” said Stéphane Bancel , Moderna’s CEO.
Marrazzo says the mRNA-based flu vaccine is a gamechanger when it comes to matching influenza strains circulating at a given time and in a given region to the flu vaccine. The better the match, the more effective the shot in preventing flu and some of its serious consequences, including pneumonia, respiratory distress, and even organ failure in those who are most vulnerable to infections, which include older people, young children, and those with weakened immune systems.
Because the mRNA technology relies on a genetic plug-and-play model, in which different genetic sequences for any virus or pathogen can be switched into the vaccine, the shot takes around six weeks to develop. Current flu vaccines, on the other hand, take up to six months to create because they require growing the influenza virus in eggs before the virus is processed into the vaccine to activate the proper immune response.
Currently, the World Health Organization (WHO) convenes a group of influenza experts each year to study the flu that circulates among populations in the southern hemisphere of the globe to determine which strains of the virus should be targeted in a vaccine for the northern hemisphere, where colder climates generally contribute to worse flu seasons. Such analysis is reliable but not always accurate, and can lead to mismatches that produce weak vaccines. “We see this play out in [vaccine] efficacy that ranges anywhere from 50% to 60% in a good year to 20% in a not-so-good year,” says Marrazzo. But with an mRNA-based flu shot, manufacturers won't need as much lead time to develop the vaccine, and could therefore better track and match influenza strains causing disease in real time.
Moderna plans to have mFlusiva available in the fall as flu vaccine campaigns start, but only for a select group of people. The FDA approved the shot for people ages 50 and older, the group that recently-revised U.S. government guidelines say should be receiving flu shots every year. The current recommendations differ from previous guidelines, which advised that anyone six years and older, including pregnant women, should be vaccinated against both flu and COVID every year. While the CDC continues to make this recommendation on its website , in January, the Trump Administration revised this guidance for routine vaccination and instead shifted the decision to vaccinate to individual families and their physicians. Disagreeing with the change, many health organizations—including the American Academy of Pediatrics , the American Medical Association, and the American College of Obstetricians and Gynecologists —continue to recommend yearly flu shots for most people.
The approval of the first mRNA flu vaccine is an important milestone for public health, says Marrazzo, but it's tempered by the current U.S. political environment that fuels skepticism about both the effectiveness and safety of vaccines in general, and about mRNA technology in particular. “We have never been technically at a more exciting time in terms of mRNA vaccines. There are all kinds of incredibly cool stuff happening," she says. "Yet in the public eye, we are taking five steps backward as trustworthy emissaries for the advancement of science, all due to the undermining of research and our credibility as trusted advisors.”
mFlusiva's road to approval exemplifies this now-fraught environment for vaccines in the U.S., after the FDA initially dropped it from review in February. The agency sent Moderna a “Refusal-to-File” letter, notifying the company that it would not review the vaccine and stating that the study did not provide a proper control arm against which to compare mFlusiva, and that using existing flu shots as comparators “does not reflect the best-available standard of care.” In prior discussions before submitting its request for approval, the FDA suggested that the company provide data comparing mFlusiva among those 65 years or older to higher dose flu vaccines for this older population, which is at higher risk of complications from flu. Moderna says it provided the additional data.
After receiving the Refusal-to-File letter, Moderna’s executives and scientists met with the FDA and agreed to seek full approval for people 50 to 64 years old, and accelerated approval for people 65 years or older, as well as conduct another study in the latter population. Under FDA’s accelerated approval, drugs can be approved sooner based on results of early benefit while further studies on longer term benefit are completed. Days after refusing to review the mRNA flu shot, the FDA decided to consider it for approval.
Marrazzo says she can’t think of another drug that experienced such about-face decision...
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