The U.S. Food and Drug Administration reversed its decision and will proceed with a review of Moderna’s experimental influenza vaccine, the company announced Wednesday, one week after the regulator unexpectedly declined to evaluate the application in a move that generated widespread industry concern about shifting vaccine approval standards under the Trump administration.
The FDA has accepted Moderna’s revised approach seeking full approval for the shot for adults aged between 50 and 64, and accelerated approval for those aged 65 and above, the company said, adding that it will also conduct a post-marketing study in older adults. The agency is expected to make a decision by August 5, providing a potential pathway for the mRNA-based vaccine to reach the market for the 2026-2027 flu season.
Moderna shares rose more than six percent in early trading following the announcement. The decision to review the company’s application comes shortly after the earlier rejection sparked major controversy.
The initial refusal, issued in a letter dated February 3, centered on objections to the design of Moderna’s clinical trial. The agency told Moderna that its application didn’t contain an “adequate and well-controlled” trial because the control arm didn’t reflect the “best-available standard of care in the United States at the time of the study.” Moderna used a standard-dose seasonal flu vaccine called Fluarix as a comparator in a 40,700-person clinical trial to demonstrate the experimental mRNA vaccine’s safety and efficacy.
FDA Commissioner Marty Makary defended that position publicly on Tuesday during an event hosted by PhRMA, the pharmaceutical industry trade group, arguing that the Centers for Disease Control and Prevention recommends that people aged 65 and older receive high-dose flu vaccines, and that Moderna’s study should have used a high-dose comparator for that age group in the control arm, not the standard-dose Fluarix vaccine.
Top Food and Drug Administration official Vinay Prasad overruled the agency’s reviewers when he refused to accept Moderna’s application for a new influenza vaccine, STAT has learned. Three agency officials familiar with the matter told STAT that the team of career scientists was ready to review Moderna’s application, and that David Kaslow, the head of the vaccine office, wrote a detailed memo explaining why the FDA should embark on the review. The decision was made by top agency official Vinay Prasad, who STAT previously reported had overruled career scientists in the vaccine center. The rejection and subsequent reversal unfolded against the backdrop of broader shifts in U.S. vaccine policy under Health and Human Services Secretary Robert F. Kennedy Jr., a longtime vaccine skeptic who has been particularly critical of mRNA technology. HHS canceled 22 projects worth about $500 million focused on mRNA vaccine development in August, claiming against evidence that “these vaccines fail to protect effectively against upper respiratory infections like COVID and flu.”
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Prasad was an outspoken critic of the government’s response to Covid-19 before he was appointed to the FDA under HHS Secretary Robert F. Kennedy Jr. He claimed late last year without providing details that Covid-19 vaccines resulted in deaths of 10 children and has said the agency will change its vaccine approval process. Prasad heads the FDA’s Center for Biologics Evaluation and Research, the division responsible for vaccine regulation.
Moderna had insisted that the FDA agreed to its trial design as recently as April 2024 and that the agency suggested during an August meeting, shortly before the company submitted its application, that it would review the filing and assess issues with the comparator during that process. The company said the FDA had agreed with that plan in April 2024 but suggested it also include data comparing its vaccine with an approved high-dose flu vaccine for people over 65, which the company said it did.
The company’s revised submission addresses the FDA’s objections by splitting the approval pathway. Adults aged 50 to 64 will be evaluated through a standard approval process, while those 65 and older will be subject to accelerated approval contingent on Moderna conducting an additional post-marketing study in that age group.
“We appreciate the FDA’s engagement in a constructive Type A meeting and its agreement to advance our application for review,” Moderna CEO Stéphane Bancel said in a statement. “Pending FDA approval, we look forward to making our flu vaccine available later this year so that America’s seniors have access to a new option to protect themselves against flu.”
Citi analyst Geoff Meacham described the reversal as an “about-face” that “potentially brings back a revenue stream which had been in limbo.” Leerink Partners analyst Mani Faroohar said the public airing of the dispute and the FDA’s quick reversal “should be a tailwind for bulls who argue Moderna can effectively leverage public pressure against” mRNA skeptics at the agency.
Moderna’s phase 3 study showed in results reported in June that the mRNA-based flu shot produced efficacy that was about 27% higher than Fluarix in adults 50 and older. A separate trial that assessed safety and immune response included the comparison with a high-dose flu vaccine for people 65 and older and showed superiority, Moderna said.
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The mRNA-based flu vaccine, if approved, would represent the first influenza shot using the technology that became the foundation of the most widely deployed COVID-19 vaccines. With currently approved technology, experts select flu strains for each fall’s seasonal vaccines during the preceding February. Moderna has pointed out that mRNA vaccines can be manufactured much faster; for Covid-19 vaccines, the design is decided in May or June, for shipping by August. Choosing the strains closer to the start of flu season could potentially lead to a better match with circulating viruses, “and better matching equals, usually, better protection.”
The reversal follows mounting concern within the pharmaceutical and public health communities about regulatory unpredictability under the current administration. Vaccine manufacturers have privately expressed uncertainty about whether previously agreed-upon trial protocols and regulatory pathways remain valid, and whether existing guidance documents still reflect the agency’s position. The Moderna case has intensified those concerns, particularly as Pfizer also has mRNA-based flu vaccines in clinical development.
The FDA’s decision to proceed with the review does not guarantee approval. The agency will now conduct a full evaluation of the safety and efficacy data submitted by Moderna before making a final determination.