FDA's Shifting Stance on Moderna's mRNA Flu Vaccine

The Food and Drug Administration’s decision, made public on Feb. 10, 2026, to not review an application to approve Moderna’s proposed mRNA-based flu vaccine set off a firestorm of criticism from public health experts.

But just a week later, on Feb. 18, the FDA backtracked on its decision, saying that it will indeed review the vaccine, potentially in time for its approval for the 2025-26 flu season. The decision sent Moderna’s stocks soaring in a rebound from the earlier decision.

Even before the FDA’s decision to reject the application, Moderna and other drugmakers were beginning to pare back investments in vaccines due to concerns about the approval process. As a law professor who studies vaccine policy, I believe the FDA’s abrupt shift is unlikely to assuage those concerns.

The FDA said it will review the vaccine for use by people age 50 to 64 under the standard review pathaway, which is how it evaluates most drugs.

In declining the application originally, the FDA claimed that Moderna did not conduct an “adequate and well-controlled” study because it had not compared patients receiving its vaccine with patients receiving what the agency claimed to be “the best-available standard of care.” The agency’s decision to review it now is effectively a reversal of that position, which was not based on any legal standard .

For people age 65 and older, the FDA said it will now review the vaccine through a long-standing program called “accelerated approval,” which is used to more quickly review drugs that “treat serious conditions” and “fill an unmet medical need,” and that show promise.

Under this faster process, the law allows the FDA to consider different data than under a standard approval. Instead of looking at final results, a company can submit results that use a proxy measurement to reflect that a drug is likely to achieve its clinical goal.

This means that if the FDA approves Moderna’s vaccine for this older age group, the company will have to conduct additional studies on it afterward. What’s unusual, though, is that the agency typically suggests the use of the accelerated approval pathway much earlier in the process, not after a company submits its application.

Federal health officials under Health and Human Services Secretary Robert F. Kennedy Jr., including at the FDA, have taken many steps over the past year that disrupt long-standing public health practices relating to vaccine access and approval. They have expressed particular skepticism toward mRNA-based vaccines, which were developed during the COVID-19 pandemic.

Kennedy and other health officials have raised concerns about safety while providing no credible data on health risks, and have defunded research on their development.

With so many areas in vaccine law and policy in turmoil, incentives for vaccine manufacturers to bring vaccines to market are shrinking. Recent changes in the FDA’s approach, including proposals on new standards for testing vaccines that many vaccine experts have called impossible to achieve, have raised major concerns.

Already, multiple vaccine manufacturers, including Moderna, have announced plans to scale back their investment in vaccine research and cut jobs.

By agreeing to review Moderna’s application for people age 50 to 64, the FDA is seemingly softening its stance on vaccines. But the agency’s unpredictable decisions – including the highly unusual way it invoked accelerated approval for Moderna’s vaccine – might not be enough to assuage manufacturers’ worries about the current state of regulatory uncertainty.