This article originally appeared on the Bloomberg School of Public Health website.
An mRNA flu vaccine is on its way.
On Aug. 5, the U.S. Food and Drug Administration approved Moderna's mFLUSIVA, the first influenza vaccine to use mRNA technology, for adults 50 and older.
The approval gives many older Americans a long-awaited new option for protection. Tens of thousands of Americans typically die from the flu every year, and the vast majority of them are 65 and older.
It's long been a public health priority to evolve flu vaccine technology—a process which currently takes more than six months to produce a shot and is prone to mismatches with the circulating strains—so that manufacturers can respond more quickly to the evolving virus, ultimately making flu shots more effective.
When it comes to those goals, Moderna's mRNA shot is "very, very promising," says Anna Durbin, a professor in the Department of International Health and director of the Center for Immunization Research.
"Most vaccinologists believe that mRNA vaccines are the future," says Durbin, who sits on the FDA panel that recommended the vaccine. Regulators in the EU, Canada, and Australia are also reviewing the vaccine, and the European Medicine Agency has separately authorized a combined mRNA COVID-flu vaccine, also by Moderna.
For now, Durbin says, the FDA approval provides a welcome new option for older Americans—but the price, demand, and availability of the shot, and what it means for existing vaccines, remain open questions.
Is mFLUSIVA safe and effective?
The FDA's committee of outside scientists, which reviews data on vaccine safety, effectiveness, and appropriate use, voted unanimously that mFLUSIVA's benefits outweigh its risks for adults 50 and older. "It was excellent," Durbin says of the data backing the vaccine.
In clinical trials, mFLUSIVA (mRNA-1010) was about 26.6% more effective at preventing laboratory-confirmed influenza illness than a traditional flu vaccine. It also produced a stronger immune response than traditional vaccines in adults 65 and older, with similar rates of severe side effects—which remained rare. That promising data led to accelerated FDA approval that expedites access to the shot for that high-risk group.
The vaccine's safety has been tested in roughly 70,000 people in clinical trials. The 2026–27 flu season will provide the first real-world data on how the vaccine performs in populations that don't typically meet criteria for clinical trials, such as organ transplant recipients, severely immunocompromised people, or people on certain medications.
Existing data from mRNA COVID vaccines bodes well for mFLUSIVA's real-world safety profile, says Durbin. "We would not expect to see a difference in the safety profile of [mFLUSIVA], because the [mRNA] platform is the same," she says. "The only thing that's different is that protein being produced: Now it's influenza as opposed to COVID."
How does the mRNA flu vaccine compare to traditional flu shots?
The standard inactivated vaccine—used in most flu shots—is grown from flu viruses in eggs, a technology that's been in use for 80 years. The virus is grown, then killed, then made into a vaccine—a process that takes months, meaning scientists must predict as early as January or February which strain will be circulating in the fall, more than six months later.
The other traditional platform is recombinant/subunit protein vaccines, which contain pieces of the flu pathogen that our immune systems learn to recognize and defend against. This method can produce vaccines faster than the egg-based process but is more expensive.
The mRNA platform gets around these challenges, says Durbin.
Rather than growing a virus or isolating proteins, mRNA vaccines deliver a short genetic script that instructs the body's own cells to produce a piece of the flu virus, training the immune system to recognize it. Because that script can be rewritten and swapped out quickly—without growing anything in eggs or cell culture—it is "without a doubt the fastest process," biologically, for updating a vaccine, says Durbin.
"The speediness—how fast you can make an mRNA vaccine—is really helpful for things like flu and COVID, where the virus changes over time," Durbin says. "This technology lends itself to being able to move more quickly and pivot to give us a vaccine that may be a better match for the upcoming flu season. If you have a vaccine that you can start making in August and have it ready for September, it can be a better match" for the [flu] strain that's actually circulating.
That speed could also change the regulatory calendar, says Durbin: The FDA's Vaccines and Related Biological Products Advisory Committee may need to meet more frequently to respond to emerging strains if mRNA flu vaccines become more widely used.
Crucially, the U.S. and many other countries have the infrastructure to quickly produce and adapt mRNA flu shots as needed, thanks to rapid vaccine development in response to the COVID pandemic, Durbin says. "Now we have the resources, we have the technology, we can scale up these mRNA vaccines quickly—all of the goods that we need to make these vaccines. COVID really stress-tested the supply chain."
When and where will the mRNA flu vaccine be available this fall?
The new shot will be an option for many older adults this year—but it's unclear how widely available it will be or how many Americans will choose it, Durbin says. How that plays out will be "interesting." FDA approval typically means that health insurance will cover the vaccine, but it may not be stocked in every pharmacy. Traditional flu shots—already formulated for this season—will remain widely available.
It's also unclear how much of the vaccine Moderna will manufacture and what price it will set.
"My guess is, if it's more expensive, you're going to have to ask for it," Durbin says. If it's less expensive or comparably priced, it could be readily available: "It may be as simple as a pharmacist asking, 'do you want an mRNA vaccine or the other type?'"
That could change if another flu strain emerges and the mRNA platform proves it can quickly produce a more effective, updated vaccine. "It behooves us, from a public health perspective, to update that vaccine and recommend that vaccine so that you have better protection," she says.
Uptake is another open question. While the shot is "excellent," anti-vaccine sentiment—particularly toward mRNA technology—may dampen demand, Durbin says. Moderna may opt for a relatively small initial rollout to gauge interest and to run more studies comparing the vaccine's effectiveness against traditional flu shots.
What will happen to traditional flu shots?
Other flu shots aren't going anywhere this season. They will still be an option for older Americans, and it could be years before mRNA shots are approved for younger Americans—a process that requires separate clinical trials.
Longer term, Durbin will be watching whether the mRNA vaccine demonstrates its effectiveness in real-world, post-licensure data, which could shape what happens to older vaccine development processes.
Typically, the CDC's Advisory Committee on Immunization Practices compares available vaccines, and if one is clearly more effective with no added safety concerns, it becomes the recommended option. In 2018, for instance, Shingrix became the CDC's recommended shingles vaccine after it proved significantly more effective than its predecessor, Zostavax, which was later discontinued and pulled from the U.S. market in 2020.
Something similar could eventually happen with flu vaccines, Durbin says—but resistance to mRNA technology could complicate that decision in a way it didn't for Shingrix.
"What I'm really looking for this flu season is if there's adequate uptake: Is this a game changer? Are we seeing better effectiveness with this vaccine? Do we really have a better flu vaccine, something we've been looking for for a long time?" she says.
"It'll be a flu season to watch."
