The FDA approved the first mRNA flu vaccine for use in older adults. Here’s what to know

By Elise Haulund, CNN

(CNN) — For older adults, the flu vaccine could look a little different this year.

Last week, the US Food and Drug Administration approved the nation’s first mRNA-based flu vaccine for use in people 50 and older. The vaccine, developed by Moderna, builds off the mRNA technology used in many Covid-19 vaccines.

This first-of-its-kind mRNA flu vaccine has faced a bumpy road to approval amid a political climate not friendly to the technology: The Trump administration has cut funding for mRNA vaccine development, and the FDA initially declined Moderna’s request to review the vaccine. But the agency’s independent vaccine advisers unanimously voted in June that the new vaccine’s benefits outweigh its risks.

“The Food and Drug Administration’s approval of a new mRNA flu vaccine is welcome news and provides another important option to help protect people from a virus that sends hundreds of thousands of Americans to the hospital each year and claims thousands of lives,” Dr. Ronald G. Nahass, president of the Infectious Diseases Society of America, said in a statement.

Here’s what you need to know about the vaccine, called mFlusiva, which is set to be available this fall.

How the mRNA flu vaccine is different

Traditional flu shots use inactivated or weakened forms or pieces of the virus to train the immune system to recognize the live virus if it enters the body.

But mRNA vaccines use a piece of mRNA, or messenger ribonucleic acid, that encodes for a viral protein.

When you receive an mRNA vaccine, your body gets the instructions to make a copy of that viral protein, which then generates the immune response that prepares you to fight off future infections.

Influenza is a virus that is constantly mutating. Each year, scientists aim to match the strains in the vaccine to the ones most likely to be dominant in the coming flu season.

“Sometimes there’s a mismatch between what was selected, despite best efforts, and what the dominant circulating strain is,” said Dr. William Schaffner, a professor of infectious diseases at the Vanderbilt University Medical Center. How closely matched the flu vaccine is to the dominant strain of the season is part of what accounts for the year-to-year changes in the shot’s effectiveness.

One limit to the currently used flu vaccine platform is that the selection of what virus strain to include must happen around February, about six months before the shots are administered. Currently, flu vaccines are manufactured by growing the influenza virus in cells or chicken eggs.

“That’s a huge challenge because it is often limiting in terms of how fast and how much vaccine we can make,” said Dr. Michael Osterholm, who directs the Center for Infectious Disease Research and Policy at the University of Minnesota.

Since mRNA vaccines can be manufactured quickly, the strain selection can occur closer to when shots are administered — in May, instead of February.

“This affords us a lot more flexibility in trying to match up the right strain of virus circulating with what’s in the vaccine,” Osterholm explained.

Who can get the vaccine

The vaccine will be available for people 50 and older, but it got two different types of approval.

Moderna’s new vaccine was granted standard approval for adults 50 to 64 years old. For adults 65 and older, it received accelerated approval, a pathway negotiated after an unusual amount of back and forth with the FDA.

The FDA had originally greenlit Moderna’s study design for the mRNA flu vaccine but then rejected the application in February before eventually agreeing on the two-pronged approval pathway.

The agency said this year that Moderna’s application didn’t contain an “adequate and well-controlled” trial because the control arm of the study didn’t reflect the “best-available standard of care in the United States at the time of the study.”

Moderna had compared the vaccine’s efficacy in adults over 50 to a standard dose flu vaccine. However, guidance from the US Centers for Disease Control and Prevention recommends an enhanced dose vaccine for adults 65 and older.

“People over the age of 65, you don’t want to compare it against a weaker vaccine,” said Dr. Gregory Poland, director of research for the Atria Research and Global Health Institute in New York, who was not involved in study on Moderna’s vaccine. “You want to compare it against one of the three vaccines that are preferentially used in older people.”

In the 65-and-older population, Moderna presented data showing that the vaccine has better ability to produce antibodies — the molecules in your body that help it recognize pathogens and fight illness — compared with an enhanced vaccine. The FDA granted accelerated approval under the condition that Moderna conduct a post-marketing study this coming flu season to ensure that that advantage in antibody production translates to a clinical advantage.

“I think the accelerated approval, with the obligation of the company to do some studies and to come back to the FDA with further data regarding effectiveness and safety, are entirely appropriate,” Schaffner said. “That’s been done for other vaccines, and that’s a program that works out well.”

How to weigh which shot to get

Moderna’s new vaccine was found to be about 27% more effective during the 2024-25 vaccine season than standard flu shots in the company’s study, which enrolled over 40,000 people older than 50.

The mRNA vaccine did show higher rates of adverse reactions compared with the standard dose vaccine. But most of those reactions — injection site pain, muscle and joint pain, nausea and vomiting, fever, headache and chills — were mild to moderate and went away within days. Serious adverse events occurred at similar low rates in study participants who received the mRNA vaccine and the standard flu vaccines, and most were assessed to be unrelated to vaccination.

People who have an allergy to any of the ingredients or who’ve had Guillain-Barré syndrome after flu vaccination in the past should not get the new vaccine.

Several experts said the new flu shot is a major step forward, and some emphasized the importance of the additional study Moderna will conduct this fall in adults older than 65 to compare mFlusiva’s clinical benefit against an enhanced flu vaccine already recommended for older people.

“The way I would summarize it is, in the 50- to 64-year-olds: good option, moderately compelling, better efficacy trade-off is about double the rate of side effects,” Poland said. But in those 65 and above, “we need what’s called real world effectiveness data and efficacy data.”

Dr. Sean Leng — a practicing geriatrician and professor of medicine at the Johns Hopkins University School of Medicine, where he directs the Center on Aging & Immune Remodeling — said that making the decision of whether to get a flu shot with his older patients is generally a simple conversation, as many of them are used to the yearly shot.

“In my view, I would need to present those options for them,” Leng said.

If Moderna finds better clinical efficacy against the enhanced vaccines, he said, “I would probably make a stronger recommendation to our patients.”

When the vaccine will be available

Moderna has said it aims to have the mRNA vaccine available this fall.

Typically, after a new vaccine is approved, the US Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices will review data and weigh in on whether the agency should recommend it. However, a federal judge ruled in March that US Health and Human Services Secretary Robert F. Kennedy Jr. did not follow federal legal procedures when he replaced all the committee’s members, and it hasn’t met since. A meeting is currently scheduled for October.

Where the vaccine could be available

Because most pharmacies and clinics order their flu vaccines earlier in the year, mFlusiva’s impact may be somewhat limited this coming season.

“We’re unsure at the moment what additional ordering levels will look like as far as pharmacies ordering and then stocking the new mRNA flu product,” said Dr. Brigid Groves, vice president of professional affairs at the American Pharmacists Association.

Dr. Michelle Fiscus, chief medical officer for the Association of Immunization Managers, said it may be easier for patients to find at larger pharmacies like CVS and Walgreens.

“I imagine there will be some demand for this vaccine … and that may mean that there’s some limited availability,” Fiscus said.

Insurance coverage for the new vaccine

In the absence of a recommendation from the CDC’s vaccine advisers, there also remains uncertainty around whether Moderna’s mRNA flu vaccine will be covered by insurance.

“Within the Affordable Care Act, it does specify what vaccines are considered covered,” Groves said. “The confusion point lies in the fact that the ACIP, within the CDC, has not had an opportunity to convene and as such, has not had a chance to review the new flu mRNA vaccine and/or issue a recommendation or guidelines around it.”

Flu vaccines are usually covered at zero copay by Medicaid and Medicare, as well as commercial insurance plans, but Groves said that “at this point, it’s unclear as to what coverage will look like.”

Moderna, HHS and the CDC did not respond to a request for comment on plans for rolling out the vaccine.

Why it’s important for older people to get a flu shot

Flu vaccines are especially important for older adults who are at a much higher risk of complications, hospitalization and death from influenza.

According to CDC data from the 2024-25 flu season, 76.9% of hospitalizations from flu were in adults older than 50, even though they accounted for only 34.4% of influenza-related symptomatic illnesses. Furthermore, 70.6% of deaths were in adults older than 65, even though they had only 8.8% of illnesses.

Flu vaccines are not designed to prevent minor illness, but they are much more effective at preventing severe illness, according to Poland.

“You might have had mild flu, but you didn’t get a plastic tube down your throat and put on a ventilator,” Poland said. “In fact, you didn’t even get hospitalized.”

Vaccines against influenza have reduced seasonal flu burden since they were introduced in the 20th century.

The flu “has large ramifications that occur each year, and so everything we can do to prevent illness — particularly the most serious illness that requires admission to hospitals, admission to the intensive care unit and admissions to the cemetery — we would like to prevent as much of that as possible,” Schaffner said. “And the influenza vaccine is the single best way we have at the moment, imperfect as it is, in impacting everything that flu does in society.”

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