First study finds mRNA flu vaccine about 27% more effective than standard-dose

FDA will approve the mRNA flu shot only for adults 50 and older

The Centers for Disease Control and Prevention reported that flu activity is rising earlier than usual, and NPR host Ayesha Rascoe told Dr. Ann Falsey, who teaches about infectious diseases at the University of Rochester School of Medicine, that “it’s not too late to get your flu vaccine.” For adults 50 and older, Rascoe said, several flu vaccines are available, including one that is new this year and built on the same technology as the COVID-19 shots.

Falsey said the first study of that vaccine came out recently and found the mRNA flu shot about 27% more effective than the standard-dose flu vaccine. She said adults 50 and older have particular reason to consider it: that group is more at risk for serious infection or illness if they catch the flu.

The two approaches work differently. The mRNA vaccine gives the body a message that instructs it to make the flu protein and mount an immune reaction, Falsey said. Traditional flu vaccines work in the other direction. “They give you a piece,” she said, with manufacturers growing the virus, often in chicken eggs or vats of cells, and then presenting part of it to the immune system.

That difference shows up in how quickly doses can be made. Traditional production has to begin six to nine months ahead of the season, because, Falsey said, “They try to guess which strains are going to be circulating in the winter.” With RNA, a manufacturer can select the antigen, the protein it wants the immune system to react against, and make it quickly, which allows a faster response if a new strain appears and a faster scale-up to more doses.

The approval carries the same boundary as the research. Falsey said the FDA will approve the mRNA flu vaccine only for the people in whom it was studied, adults 50 and older. Asked whether the shot could be given to younger people, Rascoe said it would work fine for them, too, and Falsey agreed that the restriction prioritizes older adults.

The mRNA option carries a trade-off of its own. RNA vaccines have “a little bit more reactogenicity,” Falsey said, so a recipient might get “a little bit more sore arm” and might feel “a little punky” the next day. “It’s always a trade-off,” she said, adding that she is “a firm believer” in RNA vaccines.

Falsey also addressed the objection she hears from people weighing the shot: that it is new and untested. RNA vaccines, she said, were not brand new when they arrived during the COVID-19 pandemic — researchers had been working on them for a couple of decades — and more time has passed and more data have accumulated since the COVID shots. She asked people with doubts to be specific about them: “tell me what your specific worry is.”

On the concern that the vaccine could integrate into a person’s DNA, Falsey said she can tell people with 100% certainty that it will not happen. “It just can’t happen,” she said, adding: “it’s just a marvelous technology that works really well, so, you know, we need to deploy it sensibly.”

Falsey does not expect RNA vaccines to displace the other flu shots. She said a segment of the population will never want one — “RNA just gives them the heebie-jeebies,” she said — and that there will always be a need for options.

For adults 50 and older, the existing choices include a high-dose flu vaccine made with protein in traditional eggs, a vaccine containing an adjuvant, which Falsey described as “a little something to goose the immune system,” and a higher-dose cell-based vaccine.

One gap remains in that lineup. Falsey said the high-dose protein vaccine and the adjuvant vaccine are not approved for people ages 50 to 64. For adults in that band who want extra protection, she said, the mRNA flu vaccine is one option.

With flu activity rising earlier than usual, the practical question for adults 50 and older is which vaccine to get, and Falsey described several options still on the table. She said a recipient of the mRNA shot might get a little bit more sore arm or feel a little punky the next day. Separately, she said, the RNA approach can be made much faster than traditional production, which allows a quicker response if a new strain appears.