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The U.S. Food and Drug Administration (FDA) on Wednesday approved the first messenger RNA (mRNA)-based seasonal flu vaccine, clearing the way for Moderna’s mFlusiva to be used in adults ages 50 and older, The New York Times reported.
The approval is a major win for Moderna, which sees mFlusiva as the next step in expanding its mRNA platform beyond COVID-19.
The move drew criticism from vaccine safety advocates, who argued that regulators should not expand the use of mRNA technology before addressing concerns raised during the COVID-19 vaccine rollout.
“mRNA gene therapy injections are demonstrably not ready for prime time,” said Mary Holland, CEO of Children’s Health Defense (CHD). “No new mRNA shots should be brought on the market, and those already on the market should long ago have been removed. It is disheartening to see the Trump administration greenlight these shots that will undoubtedly have severe adverse consequences.”
Moderna President Stephen Hoge praised the approval, calling it “a big deal for us.”
The company now has “vaccines against all of the main respiratory pathogens that people face every year — COVID, flu and RSV, he said. “And hopefully, over time, even bring forward things like the combination vaccine.”
The approval comes as debate about mRNA technology continues.
U.S. Health Secretary Robert F. Kennedy Jr. has criticized mRNA COVID-19 vaccines, calling them “the deadliest vaccine ever made.” The U.S. Department of Health and Human Services (HHS) last year canceled nearly $500 million in funding for mRNA vaccine research, NBC News reported.
HHS Press Secretary Emily Hilliard told The Defender that Kennedy believes mRNA products require “heightened scientific scrutiny” and pointed to the FDA’s post-market monitoring requirements for mFlusiva, particularly for adults ages 65 and older.
Hilliard also noted that Centers for Disease Control and Prevention (CDC) recommendations have not yet been issued, the vaccine is not mandated and Americans should have access to transparent safety information and the ability to make decisions with their physicians regarding “whether — and which — seasonal flu vaccine is right for them.”
Published studies have linked COVID-19 mRNA vaccines to adverse events, including myocarditis and pericarditis, seizures and cancers.
Questions also remain about whether patients will be able to choose a non-mRNA flu vaccine and whether insurance will cover the newly approved shot while the CDC’s vaccine advisory committee remains unable to meet pending the outcome of a lawsuit against Kennedy and HHS.
Moderna said it expects mFlusiva to be available for the 2026-27 respiratory virus season.
Will patients really get to choose which flu shot they get?
Although doctors can now prescribe mFlusiva, some experts say many patients won’t know which flu vaccine they’re getting.
Dr. Meryl Nass, an internist and longtime vaccine safety advocate, said several types of flu vaccines are already available, including egg-based, cell culture-based and recombinant shots.
They differ in how they’re made and in how much antigen they contain. Some recombinant vaccines are produced in dog kidney cells or worm cells and, according to their labels, contain residual DNA and proteins from those cells.
Nass said patients generally aren’t given a choice among the available flu vaccines, and she doesn’t expect that to change with mFlusiva.
“When you request a flu shot, you will not receive the one you desire,” Nass wrote on Substack. “Instead you will be given one of these shots, chosen by others for you. You will not be told there exists a menu of shots to choose from.”
Insurance coverage is another unanswered question.
Vaccines are typically recommended for routine use by the CDC’s Advisory Committee on Immunization Practices (ACIP). However, a federal judge has temporarily blocked the committee from meeting.
Boston Children’s Hospital vaccine researcher Dr. Ofer Levy told NBC News that mFlusiva can still legally be prescribed without an ACIP recommendation.
But private insurers generally cover only the vaccines recommended by ACIP, and federal programs such as Medicaid and Vaccines for Children also rely on the committee’s recommendations, he said.
As a result, it’s still unclear whether private insurance, Medicare or Medicaid will routinely cover mFlusiva while ACIP remains unable to meet.
FDA did not respond to requests for comment from The Defender.
Moderna cites faster timeline and better efficacy
The FDA granted traditional approval of mFlusiva for adults ages 50-64 and accelerated approval for adults 65 and older. Moderna agreed to conduct an additional study to confirm the vaccine’s benefit in the older age group.
mRNA technology works differently from traditional vaccines. It instructs the body’s cells to produce a viral protein that triggers an immune response. The technology became widely known through the COVID-19 vaccines.
Supporters say one of mRNA’s biggest advantages is speed. Moderna says it can produce mFlusiva within two to three months after selecting the circulating flu strains, compared with about six months for conventional flu vaccines.
Hoge said the faster timeline could make it easier to update the vaccine “in a year where there’s a mismatch or, heaven forbid, there’s a pandemic for influenza again in the future.”
Levy likewise told NBC News that selecting vaccine strains closer to flu season could improve effectiveness.
“If you’re choosing the strain half a year before, how good can we be at sharpshooting?” he asked.
Approval expands Moderna’s platform of controversial mRNA vaccines
The approval moves Moderna closer to its goal of expanding its mRNA platform. The company’s combined COVID-19 and flu vaccine has already been approved in the European Union, though Moderna withdrew its U.S. application last year.
Combined vaccines have drawn increased scrutiny in recent years. For example, studies have linked the combined MMRV (measles-mumps-rubella-varicella) vaccine to higher rates of febrile seizure and autism compared with separate vaccinations.
Moderna also makes mResvia, an mRNA-based RSV vaccine approved for adults ages 60 and older and certain high-risk adults ages 18-59. The company previously halted a clinical trial of an mRNA RSV vaccine in infants after interim data showed a higher rate of severe RSV illness among vaccinated babies.
Moderna is also exploring mRNA technology beyond infectious diseases.
The company recently began an early-stage trial of an mRNA cancer vaccine designed to train the immune system to recognize proteins found in tumors. However, some researchers have raised questions about potential risks associated with experimental mRNA cancer vaccines, though the technology remains in early-stage testing.
The company is counting on its flu vaccine and future combination shot to help replace declining COVID-19 vaccine sales.
Reuters reported that analysts do not expect mFlusiva to generate meaningful revenue until the second half of 2027 because Moderna missed contracting deadlines for the 2026 U.S. flu season.
Jefferies equity analysts forecast about $750 million in combined U.S. sales of Moderna’s flu and combination COVID-19-flu vaccines by 2030, according to Reuters.
FDA approval comes after unusual regulatory reversal
The approval follows a dramatic reversal by the FDA.
In February, the agency refused to review Moderna’s application, saying the company had not conducted an “adequate and well-controlled” clinical trial and had failed to use the “best-available standard of care.”
The rare refusal-to-file letter was signed by Dr. Vinay Prasad, then-director of the FDA’s Center for Biologics Evaluation and Research (CBER). Bloomberg previously reported that such letters are issued in only a small percentage of FDA applications.
The FDA later reversed course and agreed to review the application. Some observers suggested political pressure and corporate lobbying helped drive the agency’s change in direction.
The review unfolded amid significant turnover at the agency.
In April, Prasad resigned from CBER for the second time in less than a year. The following month, FDA Commissioner Marty Makary resigned amid reports that he would be fired.
The FDA also dismissed Tracy Beth Høeg, M.D., Ph.D., the agency’s top drug regulator and a vocal advocate for vaccine safety.
In June, the FDA’s Vaccines and Related Biological Products Advisory Committee unanimously recommended approval after reviewing Moderna’s Phase 4 clinical trial.
Committee member Dr. Flor Munoz-Rivas told HealthCare Dive, “The studies that were presented today were very well conducted. They have very clear results that are very robust.”
Karl Jablonowski, Ph.D., CHD senior research scientist, took a different view. Shortly after the vote, he warned that “the unanimous vote guarantees a lot of really good questions of harm will have to be answered in the post-marketing period, when that harm manifests in the population.”
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‘The importance of the unvaccinated is lost on the vaccine company’
Moderna enrolled nearly 41,000 adults ages 50 to 64 in its mRNA flu vaccine study. About half received mFlusiva, while the other half received a traditional flu vaccine.
During the study, 411 people in the mFlusiva group developed flu, compared with 557 people who received the comparison vaccine. Moderna reported that as a relative efficacy of about 27%.
Jablonowski told The Defender that the results need to be viewed in the context of the 2024-25 flu season.
“mFlusiva was tested in the 2024-25 flu season,” he said. “In that season, the Cleveland Clinic found the available flu vaccines to have negative 27% efficacy. A vaccinated person was 27% more likely to get the flu than an unvaccinated person.”
He pointed out that Moderna compared mFlusiva with another flu vaccine rather than with an unvaccinated control group.
“The importance of the unvaccinated is lost on the vaccine company, and the FDA doesn’t care,” Jablonowski said.
He also questioned how the CDC calculates flu vaccine effectiveness.
“The flu vaccine effectiveness tracked by the CDC relies on the inferior test-negative design,” he said. “The 2024-25 season is tied for the second most efficacious season on record at 56% efficacy, the same season that was measured at negative 27%.”
Jablonowski said a placebo-controlled trial could have provided more clarity.
“If the Cleveland Clinic’s study is correct, anything that did not diminish the immune system more than the flu vaccine, even a placebo, would appear relatively efficacious against the flu — making the timing of Moderna’s clinical trial more than a little fortuitous,” he said. “A placebo arm of the study could have negated doubts raised by relative efficacy.”
Jablonowski: Approval means controlled trial will never happen
The trial also found higher rates of adverse events among people who received mFlusiva. Nearly two-thirds reported injection-site pain, while 45% reported fatigue and 38% reported headaches. Those rates were roughly twice as high as those reported in the comparison group.
Investigators considered one case each of fainting, hospitalization for low blood pressure and perimyocarditis to be related to the vaccine, the Times reported.
Immunologist and biochemist Jessica Rose, Ph.D., previously told The Defender that six months of follow-up is not enough to detect possible long-term adverse events.
She said she expects mRNA-1010 to present “exactly the same problems as for the COVID shots, as per the millions of reported adverse events to pharmacovigilance databases.”
Jablonowski said the FDA’s approval of mFlusiva means researchers may lose the opportunity to study potential safety concerns in a controlled setting.
“There were very troubling adverse effects observed in the clinical trial,” he said. “Due to Wednesday’s approval, they will not be investigated in a controlled trial.”
Related articles in The Defender
- Moderna Pulls Application for FDA Approval of Flu-COVID Shot After FDA Calls for New Clinical Trials
- ‘Bad Idea’: Moderna Launches mRNA Cancer Vaccine Trial as Experts Warn of Risks
- Breaking: Moderna’s mRNA Flu Vaccine Gets Unanimous Thumbs-Up Despite Risks, Low Efficacy
- Moderna ‘Shocked’ After FDA Scuttles Review of New mRNA Flu Vaccine
- ‘Textbook Conflict of Interest’: Did Blackstone Pressure FDA to Reverse Course on Moderna mRNA Flu Vaccine?
