The Food and Drug Administration on Wednesday approved the first mRNA flu vaccine, enabling use of a technology that will make it easier to rapidly target a widely prevalent or particularly virulent strain of the virus.
The approval of the vaccine, called mFLUSIVA, which is manufactured by Moderna, follows a series of blows to mRNA research directed by Health Secretary Robert F. Kennedy Jr., including the cancellation of 22 projects meant to develop vaccines with mRNA technology through the government’s Biomedical Advanced Research and Development Authority.
Initially the F.D.A. had refused to even review Moderna’s application for approval earlier this year, but quickly reversed course after a public outcry. The flu kills more than 300,000 people worldwide each year and was particularly harsh in the 2024-25 season, with an estimated 45,000 deaths in the United States, including at least 297 reported cases in children, according to the Centers for Disease Control and Prevention.
The new vaccine is authorized for people ages 50 to 64. The F.D.A. issued an accelerated approval for adults 65 and older, which allows widespread use and can be converted to a full approval if the results of a follow-up study are deemed acceptable.
The company said it expected to have the vaccine ready for the 2026-27 respiratory virus season.
“Flu remains a significant public health challenge, and mFLUSIVA provides an important new option for America’s seniors,” Stéphane Bancel, Moderna’s chief executive, said in a statement. “This approval also reflects the ongoing potential of our mRNA platform to help address important public health challenges through continued scientific innovation.”
MRNA technology instructs the body to produce a fragment of a virus that then sets off the body’s immune response. It was the technology used in Covid vaccines that were given to hundreds of millions of people around the world. Two scientists were awarded a Nobel Prize in 2023 for their work on mRNA technology.
As a vaccine activist in 2021, Mr. Kennedy had petitioned the F.D.A. to pull mRNA Covid vaccines off the market six months after their initial rollout.
In the case of flu, scientists believe that mRNA technology offers an advance from traditional vaccine options that take several months to prepare using decades-old technology, some requiring the virus to develop in fertilized eggs. Moderna has said that the faster new approach will enable a shift away from the current process of focusing on one flu strain for an entire hemisphere each season and allow each nation to pick its best option.
“Having a flu vaccine that does not have to go through the archaic process of using chickens and eggs will benefit the public health enormously,” said Dr. Georges C. Benjamin, the chief executive of the American Public Health Association. “It will allow us to rapidly adjust to rapidly emerging new flu strains, a capacity we have not had before.”
The company enrolled nearly 41,000 people who were 50 to 64 years old in a major study that found that the vaccine was effective but had more side effects than a vaccine manufactured with older technology. In the study, about 21,000 people took the Moderna vaccine and about the same number took the comparator vaccine. Within six months, 411 of the Moderna recipients got the flu compared with 557 of those who took the other flu shot. That translated to a relative efficacy of about 27 percent.
But those taking the Moderna shot reported more side effects: Nearly two-thirds reported injection-site pain, 45 percent reported fatigue and 38 percent reported a headache — rates about two times greater than those of the comparator. Serious events that researchers deemed related to the Moderna vaccine included a case of fainting, a case of low blood pressure that led to a three-day hospitalization and a case of perimyocarditis, or inflammation of the lining of the heart and the heart muscle.
The F.D.A.’s initial refusal to review the Moderna vaccine was a highly unusual move toward an established company that conducted a large and generally positive clinical trial. It came from the desk of Dr. Vinay Prasad, who at the time was the head of the agency’s vaccine division. Dr. Prasad had gained prominence as a sharp-eyed academic critic of pharmaceutical companies and the F.D.A. He later became a vocal supporter of Mr. Kennedy.
Dr. Prasad’s chief criticism of Moderna’s flu vaccine application was that it compared the company’s vaccine with one made by GSK that is not considered the best in class. Such a tactic, in Dr. Prasad’s view, was meant to skew the results in Moderna’s favor.
After a public outcry, Dr. Marty Makary, the F.D.A. commissioner at the time, soon backtracked, calling the rebuff “part of a conversation” the agency has with drugmakers. The F.D.A. soon began a review of the company’s application.
Rebecca Robbins contributed reporting.
