Why is the FDA refusing Moderna’s application for a new mRNA flu vaccine?

The U.S. Food and Drug Administration is refusing to consider Moderna’s application for a new flu vaccine made with Nobel Prize-winning mRNA technology, the company announced Tuesday.

The news is the latest sign of the FDA’s heightened scrutiny of vaccines under Health Secretary Robert F. Kennedy Jr., particularly those using mRNA technology, which he has criticized before and after becoming the nation’s top health official.

Moderna received what’s called a “refusal-to-file” letter from the FDA that objected to how it conducted a 40,000-person clinical trial comparing its new vaccine to one of the standard flu shots used today. That trial concluded the new vaccine was somewhat more effective in adults 50 and older than that standard shot.

The letter from FDA vaccine director Dr. Vinay Prasad said the agency doesn’t consider the application to contain an “adequate and well-controlled trial” because it didn’t compare the new shot to “the best-available standard of care in the United States at the time of the study.” Prasad’s letter pointed to some advice FDA officials gave Moderna in 2024, under the Biden administration, which Moderna didn’t follow.

According to Moderna, that feedback said it was acceptable to use the standard-dose flu shot the company had chosen—but that another brand specifically recommended for seniors would be preferred for anyone 65 and older in the study. Still, Moderna said, the FDA did agree to let the study proceed as originally planned.

The company said it also had shared with FDA additional data from a separate trial comparing the new vaccine against a licensed high-dose shot used for seniors.

The FDA “did not identify any safety or efficacy concerns with our product” and “does not further our shared goal of enhancing America’s leadership in developing innovative medicines,” Moderna CEO Stephane Bancel said in a statement.

It’s rare that FDA refuses to file an application, particularly for a new vaccine, which requires companies and FDA staff to engage in months or years of discussions.

Moderna has requested an urgent meeting with FDA, and noted that it has applied for the vaccine’s approval in Europe, Canada, and Australia.

In the last year, FDA officials working under Kennedy have rolled back recommendations around COVID-19 shots, added extra warnings to the two leading COVID vaccines—which are made with mRNA technology—and removed critics of the administration’s approach from an FDA advisory panel.

Kennedy announced last year that his department would cancel more than $500 million in contracts and funding for the development of vaccines using mRNA.

The FDA for decades has allowed vaccine makers to quickly update their annual flu shots to target the latest strains by showing that they trigger an immune response in patients. That’s a far more efficient approach than running long-term studies tracking whether patients get the flu and how they fare. In an internal memo last year, Prasad wrote that the streamlined method would no longer be permitted—leading more than a dozen former FDA commissioners to pen an editorial condemning the statements.
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—Lauran Neergaard and Matthew Perrone, Associated Press

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