The U.S. Food and Drug Administration (FDA) has refused to review Moderna’s application for its experimental mRNA-based seasonal flu vaccine, the company announced on Tuesday (February 11). The decision represents a significant setback for the biotechnology company and comes amid broader changes to vaccine policy under the current administration.
In a statement, Moderna said the FDA’s refusal did not identify any specific safety or efficacy concerns with the vaccine. Instead, the agency objected to the clinical trial design, claiming it lacked an “adequate and well-controlled” study because the control arm didn’t reflect the “best-available standard of care in the United States.”
Moderna’s president, Dr. Stephen Hoge, expressed surprise at the decision, telling CNN, “The complete stunner here is at no point in any of this did anybody say that it was not adequate” to run the clinical trial as previously discussed with the agency.
The company used a standard-dose seasonal flu vaccine called Fluarix as a comparator in its 40,700-person clinical trial. Moderna claims the FDA had previously agreed to this approach in April 2024, with the suggestion to also include data comparing its vaccine with an approved high-dose flu vaccine for people over 65, which the company says it did.
The refusal letter was signed by Dr. Vinay Prasad, director of the FDA’s Center for Biologics Evaluation and Research, who was appointed under Health and Human Services Secretary Robert F. Kennedy Jr. Kennedy’s administration has taken a more skeptical stance toward mRNA technology, canceling 22 projects worth about $500 million focused on mRNA vaccine development in August.
Moderna CEO Stéphane Bancel criticized the decision, saying it “does not further our shared goal of enhancing America’s leadership in developing innovative medicines.” The company’s stock fell approximately 7% in after-hours trading following the announcement.
The experimental flu shot showed promising results in phase three trials last year, with efficacy about 27% higher than Fluarix in adults 50 and older. The vaccine was seen as key to Moderna’s efforts to develop a combination vaccine targeting both influenza and COVID-19.
Moderna has requested a meeting with FDA officials to understand how to proceed. Meanwhile, regulatory reviews are continuing in the European Union, Canada, and Australia, with the company expecting its first approval to likely come in Europe later this year.
“Refuse-to-file” letters are relatively rare from the FDA. A 2021 study of almost 2,500 applications submitted to the agency found that only 4% received such letters.
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