A new kind of flu shot will soon be available in the United States.

The Food and Drug Administration (FDA) has recently approved Moderna’s mFLUSIVA, the first mRNA-based flu vaccine, for adults aged 50 and above. This type of vaccine, also used to protect against COVID-19, provides cells with instructions to produce an antigen that trains the immune system to respond to the virus.

“Every year, we chase changes in the flu virus to create new vaccines. Now the mRNA vaccine is more nimble. It’s easier to produce, and the turnaround time from intent to final product is really short,” Onyema Ogbuagu, MD, an infectious diseases specialist and professor of medicine and pharmacology at Yale School of Medicine, told Verywell.

“It is superior to prevailing vaccines and particularly better for populations that are quite disproportionately impacted by the flu,” he added.

How Effective Is Moderna’s mRNA Flu Shot?

A clinical trial found that mFLUSIVA was 26.6% more effective than the standard flu shot for adults 50 and older. Only 2% of participants who received mFLUSIVA developed the flu, compared with 2.8% who received the standard-dose vaccine.

Another clinical trial compared mFLUSIVA with Fluzone High-Dose, a vaccine designed for older adults. Researchers found that mFLUSIVA helped the body build a stronger immune response in adults 65 and over. However, research is ongoing to confirm whether that translates into better protection against the flu in this age group.

“The recent study only compared and was more effective than the standard dose vaccine in adults over 50,” Rebecca Wang, MD, an infectious disease physician at Dartmouth Hitchcock Medical Center, said. “It’s hard to say for sure that someone age 65 should get this new mRNA instead of the enhanced vaccine that’s already out there.”

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How Is the mRNA Flu Shot Different From a Traditional Flu Shot?

Commonly made using egg-based manufacturing, traditional flu vaccines introduce bits of influenza virus proteins into the body. This then trains the immune system to build a response that protects itself from the flu.

The mFLUSIVA vaccine works by giving cells instructions to make the flu virus’s surface protein, which teaches the immune system to recognize this protein and build antibodies against it. An mRNA vaccine can be updated more quickly to match circulating flu strains and may produce a stronger immune response against influenza A and B than the traditional flu shot.

That could be especially important for older adults, who may not develop a strong enough immune response to existing flu vaccines, Ogbuagu said. Currently, flu vaccines vary drastically in effectiveness from year to year, reducing the risk of hospitalizations by 19%–60%.

“There’s a need for a vaccine platform that also boosts seroresponse rates, where people are more likely to generate the protective antibody response,” Ogbuagu said.

What Are the Side Effects?

During the clinical trials, participants who received the mRNA vaccine reported side effects including pain at the injection site, tiredness, headache, and muscle or joint pain. These reactions were relatively mild and similar to those associated with the standard flu shot.

“Rates of serious adverse events were quoted at 2.2% in those who got the mRNA vaccine, compared to 1.9% who got the standard dose vaccine,” Wang said. “That’s pretty low rates of serious adverse events in both groups.”

Ogbuagu said that symptoms like headache and fatigue are just a marker that the body’s immune system is responding to the vaccine.

“We actually found in COVID vaccines, for example, that people who have more of those local symptoms tended to have higher immune responses,” he added. “And, of course, that’s the best correlate for clinical protection that we have.”

When Will It Be Available?

Although Moderna says that the mFLUSIVA is expected to arrive for the 2026-2027 flu season, it has not been recommended by the Advisory Committee on Immunization Practices (ACIP), a medical expert panel at the CDC.

ACIP recommendations allow vaccines to be covered by most insurance. It is not yet clear how much the new vaccine will cost out of pocket and whether insurers will cover it this year.

Wang doesn’t expect mFLUSIVA to be widely available at pharmacies this year.

“Many hospitals are already creating their formularies for this respiratory season,” she said. “At Dartmouth, we signed our contract for our flu vaccine back in February. I’m curious to see how things unfold next season, and I think a number of things will drive that, including cost.”

Wang encourages people to get their flu shots, regardless of whether mFLUSIVA is available. “I want to make sure that people don’t forget that it is currently a risk. Last year was a bad flu season,” she said. “This year, I think, could also shape up that way.”