The FDA’s approval of an mRNA flu shot presents a new, long-awaited option
On August 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.
“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 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.”
Annalies Winny is a senior writer in the Office of
External Affairs at the Johns Hopkins Bloomberg School of Public Health.
