Moderna’s mRNA Flu Vaccine Approved by FDA

The agency requires more data to prove efficacy for over 65s, but has licensed the first mRNA-based flu shot in the United States for those aged 50–64.

Moderna bivalent COVID-19 vaccine at a clinic, in Richmond, Va., on November 17, 2022. AP Photo/Steve Helber, File

The U.S. Food and Drug Administration has approved Moderna’s flu shot for over-50s, marking the first time the agency has licensed a messenger ribonucleic acid (mRNA) vaccine ​for seasonal influenza.

The shot, known as mFlusiva, was given a traditional approval for adults aged ‌50 to 64, and an accelerated approval for the over-65s, the pharmaceutical giant said on Wednesday.

Moderna has agreed to run an additional study and submit further data on the over-65s in a bid to demonstrate the vaccine’s benefit for that age group.

The approval was based on data from a ⁠late-stage trial involving more than 40,000 adults aged 50 and older, which found the shot was ​26.5 percent more effective than a licensed standard-dose flu vaccine.

Moderna had to submit separate late-stage data showing the ​shot generated stronger antibody responses than Sanofi’s high-dose flu vaccine in the over-65s after problems with the methodology in its phase 3 trial.

The vaccine uses mRNA technology, intended to prompt the body to produce influenza ​antigens and trigger an immune response. Scientists say this approach could potentially allow faster updates of the shot to match ​the ever-shifting circulating strains.

Health Secretary Robert F. Kennedy Jr., who oversees the FDA, announced in August 2025 that the Department of Health and Human Services (HHS) was winding down mRNA vaccine development activities under the Biomedical Advanced Research and Development Authority. He said that funding would be redirected away from developing mRNA vaccines toward “safer, broader vaccine platforms that remain effective even as viruses mutate.”

Several FDA officials who had voiced opposition to mRNA vaccines have recently departed the agency.

Flu vaccines can range in effectiveness depending on the season, peaking at 60 percent and dropping to as low as 10 percent in the 2004–2005 season, according to estimates from the Centers for Disease Control and Prevention.

The CDC and the FDA both recommend annual vaccines for everyone in the United States, including babies once they are 6 months old.

‘Important New Option’

“Flu remains a significant public health challenge, and mFLUSIVA provides an important new option for America’s seniors,” Moderna said in an Aug. 5 statement.

MFlusiva will compete with existing flu vaccines from Sanofi, GSK, CSL Seqirus, and AstraZeneca. Conventional flu shots are largely egg-based and contain viral proteins.

Officials in the spring try to predict which strain of flu will be circulating in the following virus season, primarily in the fall and winter, giving manufacturers about six months to produce shots with updated formulations.

This process can result in a mismatch between targeted and circulating strains, an issue that the FDA and Moderna said the mRNA shot could address.

Signage outside of the Food and Drug Administration headquarters in White Oak, Md., on Aug. 29, 2020. Andrew Kelly/Reuters

Higher Rates of Adverse Events

The trial found the Moderna flu shot caused higher rates of adverse events in recipients than the already available vaccines, with side effects including fatigue, headaches, and muscle pain. Serious adverse events were reported in 2.2 percent of the recipients of the mRNA vaccines—with three events considered by the investigator to be vaccine-related—and in 1.9 percent of those who received the standard-dose comparator vaccine.

Vaccines containing mRNA are cleared in the United States for COVID-19 and respiratory syncytial virus.

The FDA in 2025 narrowed the approval for Moderna COVID-19 vaccines, known as Spikevax, and for Pfizer-BioNTech’s rival shot, known as Comirnaty, both of which use mRNA technology.

A French peer-reviewed study published in 2022 concluded that mRNA COVID-19 shots from Pfizer and Moderna were found to increase the risk of both myocarditis and pericarditis, particularly in adolescent and young adult males after the second dose.

Moderna withdrew its application for ​a COVID-flu combination shot last year after the FDA sought additional evidence demonstrating ​the effectiveness ⁠of its flu component. European regulators in April approved the combination shot.

Lost Revenue

Moderna had been counting on the combined shot and the flu vaccine to replace some of the lost COVID vaccine revenue and to prove the long-term commercial potential of ​mRNA technology.

Jefferies analysts had forecast $750 million generated from U.S. sales of Moderna’s flu shot and its combination COVID-flu vaccine by 2030.

FDA reviewers said on June 16 that uncertainties remained about the efficacy of mFLUSIVA, then known as mRNA-1010 before its approval, due to an issue with trial methodology.

The phase 3 trial compared the immunogenicity and clinical results in a group that received Moderna’s vaccine with the results from a group that received an authorized, standard flu vaccine.

The U.S. government, though, recommends a higher-dose flu vaccine than a standard shot for adults aged 65 and older.

In a 92-page document, FDA reviewers said, “This limitation affects interpretation of the net clinical benefit in the 65 and older population and is a key issue for Advisory Committee deliberation.”

Other lingering questions included vaccine safety, given that adverse reactions were more common among mRNA-1010 recipients, the report said.

Moderna Connections

Multiple FDA committee members who voted in favor of the approval have connections to Moderna, including El Sahly and Dr. Flor Munoz, who was a Moderna adviser from 2022 to 2024 and played a role in recommending that pregnant women should receive COVID-19 vaccines.

Moderna’s withdrawal of its combined Flu and COVID-19 shot came amid heightened FDA scrutiny of vaccines under the agency’s previous leadership.

Former FDA Commissioner Marty Makary and former vaccine chief Vinay ⁠Prasad departed the agency earlier this year.

Makary had faced criticism from companies, lobbyists, and others for agency officials declining to approve certain drugs, including a cancer drug made by Replimune. Makary had defended the decisions in television interviews as following the evidence.

Zachary Stieber and Reuters contributed to this report.