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By Melissa Fleur Afshar
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The government spent months trying to keep one vaccine off the market, but now it is approved and headed for the over 50s browsing pharmacy shelves this winter.
The Food and Drug Administration (FDA) has granted approval to mFLUSIVA, Moderna's mRNA-based seasonal influenza vaccine, making it the first flu shot built on the same technology behind the company's COVID-19 vaccine to reach the U.S. market.
The approval, which happened on August 5, covers adults aged 50 and older—a narrower rollout, but one that accounts for how older populations are more susceptible to serious illness from flu.
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Despite some initial concerns, the shot outperformed a standard-dose flu vaccine in a clinical trial involving 40,703 people, which led to a glowing review in The Lancet. Still, the vaccine's use in adults aged 65 and older remains under "accelerated approval" pending a confirmatory study, meaning it was conditionally approved to reach the most vulnerable, but the manufacturer must still conduct additional studies to confirm its efficacy.
Though it created a stronger immune response than standard-dose flu vaccines, 26.6 percent to be exact, mFLUSIVA did not stand out when cast alongside every enhanced flu vaccine option already recommended for older adults.
Moderna says mFLUSIVA could be available for eligible adults from November.
Newsweek has contacted the FDA via email for comment.
What Exactly Did the FDA Approve?
The FDA's product listing identifies mFLUSIVA as "Influenza Vaccine, mRNA," manufactured by ModernaTX, Inc., and authorized for preventing influenza disease caused by the A and B strains in the over 50s.
Crucially, the clearance splits into two tiers; standard approval for ages 50 to 64, based on efficacy data, and accelerated approval for the 65-and-older group, granted on the strength of immune-response data alone and contingent on Moderna completing an additional confirmatory trial.
What Makes This Vaccine Different?
Unlike egg-based or cell-based flu vaccines, mFLUSIVA contains no viral protein grown in eggs or cells at all.
Instead, it delivers the molecule messenger RNA instructions that prompt the body's own cells to briefly produce hemagglutinin (HA) proteins from the target flu strains, triggering an immune response without live or inactivated virus.
That also means no egg proteins, antibiotics, or preservatives in the manufacturing process.
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More broadly, mRNA vaccines use a copy of messenger RNA to help the body create an immune response.
What Did the Clinical Trial Show?
In the pivotal trial, 2 percent of mFLUSIVA recipients developed flu-like illness, compared with 2.8 percent among those given a standard-dose comparator vaccine—a relative efficacy advantage of roughly 26.6 percent, according to The New England Journal of Medicine.
This was a head-to-head comparison against a standard-dose shot, not a placebo, and not against every enhanced flu vaccine already available to seniors.
Side Effects and Safety
Trial participants reported more injection-site soreness, fatigue, headache, chills and muscle aches with mFLUSIVA than with the standard-dose comparator, though researchers characterized most reactions as "mild to moderate" and short-lived.
The most common side effect was pain at the injection site, with 68.7 percent of participants aged 50 to 64 reporting it, while 41.9 percent reported headaches.
Severe allergic reactions can occur but are rare. The only contraindication listed in the prescribing information is that those allergic to mFLUSIVA should not take it.
Who Should Choose This Vaccine?
Adults under 50 are not covered by this approval and should stick with an age-appropriate, CDC-recommended flu vaccine or take other precautions.
Adults 50 to 64 are a newly eligible group and should discuss the option with a clinician where available, ensuring they reveal their medical history or any allergies.
For adults 65 and older, the calculus is more layered. The CDC already preferentially recommends "enhanced" flu vaccines—high-dose, recombinant, or adjuvanted formulations—for this age group, so the question becomes whether mFLUSIVA, still under accelerated approval, is the right pick versus those established options. This is a conversation that should be had with clinicians.
What This Could Mean for Future Flu Seasons
The bigger promise of mRNA technology is speed. Because it does not require growing virus in eggs or cells, manufacturers say strain updates could theoretically be produced in as little as eight weeks—a potentially significant advantage if a mismatched or rapidly mutating strain emerges mid-season, and a capability public health officials view as especially valuable for future pandemic preparedness.
Winter flu itself, though often dumbed down as a common cold, kills between 6,000 and 52,000 people per year in the U.S. The hope is that new vaccines like this can save many of those lives. But researchers caution that although faster updates are a potential advantage, they are not a guarantee of superior effectiveness every single season.
The approval itself was hardly assured, after Health Secretary Robert F. Kennedy Jr., a longtime skeptic of mRNA vaccine safety, pushed the HHS to cancel nearly $500 million in mRNA vaccine research funding in 2025.
In February, then-FDA biologics chief Vinay Prasad overruled career staff and told Moderna the agency would not even consider its application—a decision reversed after Moderna went public.
Prasad left the FDA in April, and by June an advisory panel unanimously recommended approval.
Contact Newsweek editors on this story: Rebecca Flood and Emma Lee-Sang
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