What to Know About the New mRNA Flu Shot

The Food and Drug Administration (FDA) has approved a new influenza vaccine, mFLUSIVA, which uses the same type of technology as some COVID-19 vaccines.

“The last flu season was very severe,” said Kaylan Christianer, MD, a primary care physician at Columbia. “As we prepare for this year’s flu season, it’s good to know that there’s a new vaccine to help prevent severe illness from influenza.”

Dr. Christianer discusses what people should know about the new flu shot and how to protect yourself against the flu.

What’s different about the new flu shot?

Influenza viruses undergo genetic changes from season to season, so flu shots need to be reformulated yearly to target the strains currently circulating. Previous flu vaccines, which are made using older technologies, take months to produce, and scientists have to predict which strains may end up circulating in our part of the world well before flu season begins. If they pick the wrong strain, the vaccine may be less effective.

The new flu shot, called mFLUSIVA, uses the same mRNA technology as some of the COVID-19 vaccines. Because mRNA vaccines can be made very quickly, they can better match the current flu strain.

How effective is the new flu shot?

The new vaccine was studied in a clinical trial of over 40,000 adults age 50 and older. In that trial, the new vaccine was about 27% more effective in preventing flu symptoms and almost 50% better at preventing people with the flu from being hospitalized than previously approved, standard-dose flu vaccines.

In a separate study, researchers found that mFLUSIVA produced a strong immune response for around six months—about the length of a typical flu season.

Over the past 15 years, seasonal flu vaccines have been anywhere from about 20% to 60% effective at preventing serious illness. It’s thought that having a seasonal flu vaccine that better matches the circulating influenza strain and produces a longer-lasting immune response will better help protect people from serious illness and hospitalization.

What are the side effects of the new flu shot?

Side effects with the mRNA flu vaccine are similar to those seen with mRNA COVID-19 vaccines, such as fatigue, headache, and body aches.

Who is eligible to get the new flu shot?

The mRNA seasonal flu vaccine was approved for adults age 50 to 64. The vaccine was also granted accelerated FDA approval for adults age 65 and older based on results of a trial comparing mFLUSIVA to a high-dose flu vaccine, though more studies are underway to evaluate safety and efficacy in this age group.

If you’re not eligible for the new flu shot, experts recommend that everyone age 6 months and up get vaccinated with one of the previously approved seasonal flu vaccines.

How serious is the flu?

Influenza can cause very serious, even deadly, illness. Between October 2024 through April 2025, the flu was linked to over 45,000 deaths and more than 700,000 hospitalizations in the U.S. alone.

Getting a flu shot is the best way to lower your risk of serious illness, hospitalization, and potentially death.