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Moderna’s own clinical trial data raise serious questions about whether the U.S. Food and Drug Administration (FDA) should have approved the company’s new mRNA flu vaccine, medical commentator John Campbell, Ph.D., said.
In a recent video, Campbell argued that the study shows only a small reduction in flu cases while reporting substantially higher rates of adverse reactions among people who received the shot.
The FDA approved Moderna’s mFlusiva this month for adults ages 50-64, with accelerated approval for adults 65 and older. It is the first mRNA flu vaccine licensed in the U.S.
Moderna said it expects the vaccine to be available for the 2026-27 respiratory virus season.
Campbell also questioned why the approval came just one year after the U.S. Department of Health and Human Services (HHS) announced a coordinated federal wind-down of mRNA vaccine development.
“One quick year later, FDA approves Moderna flu vaccines,” Campbell said. “I don’t understand the way the U.S. work[s], but it would appear that HHS isn’t in charge.”
Efficacy of mRNA flu vaccine is ‘not very impressive’
Moderna’s Phase 3 trial, published in The New England Journal of Medicine, enrolled 40,703 participants, with roughly half receiving the experimental mRNA vaccine and the other half receiving a standard flu vaccine. Participants were followed for a median of 181 days.
Laboratory-confirmed flu occurred in 2.0% of participants who received the mRNA vaccine, compared with 2.8% of those who received the standard vaccine. Moderna described those results as showing a relative vaccine efficacy of 26.6%.
“Not very impressive, to be quite honest,” Campbell said.
He noted that the study showed a risk reduction of less than 1%.
“If you’re going from a 2.0% absolute to a 2.8% absolute,” Campbell said, “I would say that’s not a 26.6% relative risk improvement — although it is statistically. But it’s a 0.8% absolute risk reduction.”
“So, do you want to take a new influenza mRNA vaccine to give you a 0.8% reduced chance of getting influenza in absolute terms? Your choice,” he said.
‘Completely unacceptable increase in the adverse reactions’
Campbell said the study showed substantially higher rates of nearly every reported adverse reaction among mRNA vaccine recipients compared with those who received the standard flu vaccine.
Injection-site pain was reported by 65.8% of mRNA vaccine recipients, compared with 29.8% of those who received the standard vaccine. Fatigue occurred in 45.1% versus 20.3%, headache in 37.8% versus 18.0%, and muscle pain in 35.4% versus 11.6%.
Campbell said the disparity extended across nearly every category of reported reactions.
“Injection site pain, way more … in the mRNA group. Redness more in the mRNA group. Swelling more in the mRNA group,” he said. “Six times more fevers in the mRNA group compared to the traditional vaccine group. … Joint pain, way more common … nausea and vomiting, more common … and chills, again, way more common in the mRNA group.”
“A completely unacceptable increase in the adverse reactions there,” he added.
mRNA flu vaccine group showed ‘6.4 times more’ potentially serious reactions
Campbell then turned to the study’s more serious adverse reactions.
Serious adverse events were reported in 2.2% of participants who received the mRNA vaccine, according to the study.
The trial also tracked Grade 3 solicited adverse reactions, which are more severe reactions that can interfere with normal activities or require medical attention. Grade 3 reactions occurred in 6.4% of mRNA recipients — “More than 1 in 20,” Campbell said — versus 1.0% of those who received the standard flu vaccine.
He compared the difference with the vaccine’s reported risk reduction in flu cases.
“So 6.4 times more adverse events, Grade 3, potentially more serious adverse events, in the mRNA group for a 0.8% absolute risk reduction according to their own figures,” Campbell said. “I really wonder why [the FDA] approved this.”
The trial also reported adverse events of special interest among mRNA vaccine recipients, including thrombocytopenia, a condition involving low platelet counts, and cardiomyopathy, which has been linked to COVID-19 mRNA vaccines.
“Looks like a bit of a no-brainer to me,” Campbell said of the mRNA flu vaccine. “I certainly wouldn’t be having it on those figures.”
‘Are you going to be queuing up? I’m not’
Campbell said his review focused on Moderna’s published trial data but noted that the study does not address broader concerns about mRNA technology.
“We could talk for ages about the lipid nanoparticles and other complications,” he said. “I’m just keeping this to what’s in the paper.”
He said lipid nanoparticles distribute throughout the body, allowing cells in different organs to produce the vaccine antigen. He argued that those cells could then become targets of the immune system.
Previously published studies have linked COVID-19 mRNA vaccines to myocarditis and pericarditis, seizures and cancers.
“Given that information, are you going to be queuing up?” Campbell asked. “I’m not.”
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‘They’re not really very safe and not particularly effective’
Campbell’s concerns about the mRNA flu vaccine also led him to question U.S. health policy.
In August 2025, U.S. Health Secretary Robert F. Kennedy Jr. announced that the Biomedical Advanced Research and Development Authority would terminate funding for 22 mRNA vaccines in development.
At the time, HHS said it had “reviewed the science, listened to the experts, and acted.”
The department said the funding was being terminated because “the data show these vaccines fail to protect effectively against upper respiratory infections like COVID and flu.”
Campbell said the FDA’s approval of Moderna’s mRNA flu vaccine appears to conflict with that policy.
“And yet a year later, here we have it approved,” he said. “Who’s in charge here? Is it not the HHS that’s in charge?”
HHS said in 2025 that it was “shifting that funding toward safer, broader vaccine platforms that remain effective even as viruses mutate.” The agency also emphasized that it supports “safe, effective vaccines for every American who wants them.”
Campbell challenged that claim as well.
“We’ve seen that they’re not really very safe and not particularly effective,” he said, adding, “Who wants them?”
Watch Campbell discuss mRNA flu vaccine risks here:
Related articles in The Defender
- ‘Not Ready for Prime Time’? FDA Approves First mRNA Flu Vaccine Despite Safety Concerns
- Moderna’s mRNA Flu Vaccine: How FDA Hid ‘Serious’ Safety Signal
- Behind Closed Doors: What the Inventor of mRNA Told Fauci About COVID Vaccines and Lipid Nanoparticles
- ‘Step in the Right Direction’: RFK Jr. Cancels $500 Million in mRNA Vaccine Contracts
- Study Explains How Some COVID Vaccines Cause Rare Blood-Clotting Disorder
