mRNA flu vaccines are making their way through clinical trials

The studies suggest that mRNA versions may be more effective than traditional flu shots

Flu vaccination remains a key public health strategy, but researchers continue to look for ways to improve the shot. Pfizer and Moderna have reported promising results for their mRNA flu vaccines in phase 3 clinical trials.

JEAN-CHRISTOPHE VERHAEGEN/AFP/Getty Images

By Aimee Cunningham

16 hours ago

This is a human-written story voiced by AI. Got feedback? Take our survey . (See our AI policy here .)

Flu vaccines that take a page from the COVID-19 vaccine platform are making progress in clinical trials.

In a phase 3 trial, Pfizer’s mRNA flu vaccine outperformed a traditional vaccine, researchers report in the Nov. 20 New England Journal of Medicine. The trial compared the two vaccines during the 2022–2023 flu season, assessing whether the percentage of participants who got the flu at least 14 days after receiving a shot was lower for the mRNA vaccine. It was, by about 35 percent. This relative efficacy measure suggests that the mRNA vaccine prevented illness more often than the traditional vaccine that flu season.

More than 18,000 healthy adults ages 18 to 64 from the United States, South Africa and the Philippines participated in the trial. The mRNA vaccine targeted hemagglutinin, a protein that allows the influenza virus to enter cells, and included versions of the protein from four flu strains. A World Health Organization committee recommends which strains to cover for each flu season.

In June, Moderna announced phase 3 trial results for its mRNA flu shot in adults 50 and older. This vaccine had a relative efficacy of about 27 percent compared with a traditional flu vaccine. That trial included nearly 41,000 participants from 11 countries. People 65 and older are at higher risk of serious complications from the flu.

An mRNA flu vaccine could be a useful new tool against the influenza virus. The mRNA platform has a faster production turnaround, which should provide more time to figure out which strains to cover. Currently, the WHO’s vaccine composition recommendation must come early enough to allow for the up to six months needed to produce traditional vaccines. If a late-breaking flu strain picks up steam, that season’s vaccine won’t be as good a match. This year, heading into the Northern Hemisphere’s flu season, a variant that arose in the Southern Hemisphere’s season is dominating flu samples in England and Japan, early data suggest. But the variant emerged too late to be recommended for the Northern Hemisphere’s vaccine.