Moderna’s newly approved mFlusiva showed a 6.4% rate of Grade 3 adverse reactions compared with 1% for a conventional flu vaccine and, based on trial figures provided, required roughly 5,000 vaccinations to prevent one additional hospitalization over the comparator.
By yourNEWS Media Newsroom
The Food and Drug Administration has approved Moderna’s mRNA influenza vaccine mFlusiva, making it the first flu vaccine using the technology to receive U.S. authorization despite trial data showing substantially more Grade 3 adverse reactions than a conventional flu shot and a comparatively small absolute difference in hospitalizations.
The decision arrives as federal vaccine oversight remains under heightened scrutiny. The Senate Permanent Committee on Investigations previously examined COVID-19 vaccine injuries that were allegedly obscured in government surveillance databases and, according to earlier reporting, suppressed at the direction of the Biden administration.
The panel, led by Sen. Ron Johnson, R-Wis., now has another vaccine-safety issue available for examination following the regulatory actions of the Trump administration.
Moderna announced late Wednesday that the FDA had approved mFlusiva. The company’s own published clinical research compared the mRNA product with an already licensed influenza vaccine rather than a placebo.
One pharmacologist reviewing the results characterized them as “not breathtaking”.
The absolute hospitalization difference reported between matched groups of roughly 20,000 participants was four cases. On that basis, approximately 5,000 people would have to receive mFlusiva instead of the conventional vaccine to prevent one additional hospitalization.
At the same time, the mRNA product produced a considerably higher rate of Grade 3 adverse reactions.
According to a Just the News report examining the approval and trial results, 6.4% of mFlusiva recipients experienced Grade 3 reactions compared with 1% among recipients of the older flu vaccine.
The figures echo previous questions involving another Moderna product. The company’s Omicron-specific COVID-19 vaccine recorded a 25% rate of Grade 3 events three years ago.
The National Institutes of Health defines Grade 3 adverse events as “incapacitating; unable to perform usual activities; requires absenteeism or bed rest.”
Moderna’s announcement preceded the appearance of the FDA’s own public approval documents. The agency’s formal mFlusiva approval information did not appear on its website until late Thursday afternoon, according to the information provided, while early media and pharmaceutical-industry reports relied on Moderna’s announcement issued at approximately 10 p.m. Wednesday.
The approval establishes two regulatory pathways.
For adults ages 50 and older, mFlusiva received approval under one indication. For adults 65 and older, it received accelerated approval.
The accelerated authorization requires Moderna to conduct a randomized postmarketing study comparing the effectiveness of mFlusiva with a high-dose influenza vaccine — the type of comparator the FDA had previously asked Moderna to use for older adults.
The agency did not respond to a media-portal inquiry asking why it authorized the vaccine given the trial results described in the material provided.
An X post concerning the FDA decision also circulated following the announcement.
The FDA had already addressed the disparity in adverse reactions in its June briefing document for the Vaccines and Related Biological Products Advisory Committee.
The agency said the reactions were “predominantly mild to moderate in severity” while emphasizing that investigators did not identify an association with heart inflammation, an adverse event that has been linked to mRNA COVID-19 vaccines.
FDA reviewers nevertheless raised concerns about limitations in Moderna’s evidence.
According to Pharma Exec, the clinical trial examined circulating influenza strains during only one flu season and did not study “immunocompromised patients or very frail older adults.”
Those populations are among those at greater risk of complications associated with influenza and potentially with mRNA vaccines.
Against the standard influenza vaccine, mFlusiva produced 26.6% relative efficacy against confirmed “influenza-like illness.”
Its reported relative efficacy against cases requiring “higher-level care (hospitalization, emergency department, or urgent care)” was 47.9%.
Moderna itself described the vaccine’s safety profile as “acceptable” in its Wednesday night release rather than using stronger language.
The regulatory history preceding approval was also contentious.
Six months earlier, then-Center for Biologics Evaluation and Research Director Vinay Prasad declined to review Moderna’s biologics license application, citing what was described as a “substandard” trial design.
Prasad, an epidemiologist, objected to the company’s failure to use a high-dose vaccine as the comparator for adults 65 and older.
Moderna, a Massachusetts biotechnology company that earned billions from its mRNA COVID-19 vaccine, subsequently warned that jobs could be moved outside the United States.
The FDA agreed approximately one week later to review the application after Moderna agreed to satisfy requirements the agency had previously established.
Some reports following Moderna’s Wednesday announcement described that sequence as an FDA rejection of the vaccine followed by a reversal.
FDA regulatory review officer Jessica Adams challenged that description in an X post Thursday.
“STOP SAYING THE FDA “REJECTED” THE MRNA FLU VACCINE AND THEN “REVERSED” IT. THERE WAS A FILING-LEVEL REJECTION OF THE ORIGINAL APPLICATION FOR TRADITIONAL APPROVAL IN ADULTS 50+. THAT IS NOT A FINAL REJECTION OF APPROVAL. IT WAS RESOLVED BY AMENDING TO A SPLIT PATHWAY. NOT A REVERSAL,” Adams wrote.
Adams separately disputed claims that FDA officials had originally rejected the application because Moderna failed to conduct a saline-placebo-controlled trial.
In another Thursday post, Adams said that interpretation was “not accurate.”
She said regulators instead objected to Moderna’s use of a “standard-dose flu vaccine as the comparator across that entire group” of older adults “for whom high-dose or adjuvanted vaccines are preferentially recommended.”
Adams further explained on X, “It was not a final rejection of approval, and it was not about lacking a saline placebo.”
A separate X post discussing the regulatory dispute accompanied discussion of how the application moved through the agency.
The approval has also intensified debate over leadership changes at the FDA.
Prasad left the agency in April, followed in May by FDA Commissioner Marty Makary. The two had been among the most prominent advocates inside the agency for stricter evidentiary standards in drug approvals.
Both had also become targets of media-driven allegations and internal criticism, including a sexual harassment allegation that The Wall Street Journal later corrected after three weeks.
Former New York Times pharmaceutical-industry reporter Alex Berenson argued that the personnel changes and mFlusiva approval represented a return of industry influence at the regulator.
The approval demonstrates that “Pharma finished recapturing” the FDA, Berenson wrote in his newsletter.
“There was no chance the FDA would say no to this jab” after the administration reportedly forced Prasad’s resignation, Berenson wrote.
Makary, however, said Prasad departed because his one-year commitment to the agency had concluded.
Berenson had previously criticized Moderna’s trial results, describing the vaccine as having a “comically bad risk-benefit ratio” after the results appeared in the New England Journal of Medicine.
He said the safety results would probably have looked “even worse” if mFlusiva had been tested against a placebo rather than an existing flu vaccine.
Another X post highlighted criticism of the mRNA vaccine’s risk-benefit profile.
The mFlusiva decision comes as other personnel developments are raising questions about the direction of federal public health agencies.
The Senate recently confirmed Erica Schwartz as director of the Centers for Disease Control and Prevention, making her the agency’s first permanent leader in nearly a year.
All but three Senate Republicans supported Schwartz despite criticism from vaccine skeptics over her earlier role in threatening prosecution of service members who refused vaccine mandates during the first Trump administration.
Only one Democrat voted for Schwartz.
Her confirmation also drew opposition after she declined to promise resistance to potential actions that could affect vaccine availability or public confidence in vaccines.
Johnson and retiring Sen. Thom Tillis, R-N.C., were recorded as absent for the vote, while Sen. Mitch McConnell, R-Ky., remains away on medical leave.
Schwartz follows Susan Monarez, the first Senate-confirmed CDC director, whose tenure ended after trust problems developed with Health and Human Services Secretary Robert F. Kennedy Jr.
The approval of mFlusiva now places the first mRNA influenza vaccine on the U.S. market with different regulatory pathways for adults 50 and older and adults 65 and older, while Moderna remains obligated to perform an additional randomized postmarketing comparison against a high-dose flu vaccine in the older population.
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