FDA Declines to Review Moderna Flu Shot, Stirring Scientific and Political Questions

The US Food and Drug Administration has refused to review Moderna’s application for approval of its flu vaccine, a move that lands at a sensitive moment for vaccine policy in the United States.

In a letter sent to the Massachusetts-based biotech company, the FDA rejected Moderna’s rationale for comparing its mRNA-1010 flu shot to a standard seasonal influenza vaccine dose. Moderna disclosed the letter on Tuesday evening, saying the agency declined to review the submission on the grounds that it lacked “adequate and well-controlled” data.

According to the company, the FDA also argued that the vaccine “does not reflect the best-available standard of care”.

Moderna disputes that assessment. CEO Stephane Bancel said the letter “did not identify any safety or efficacy concerns with our product”.

The refusal to even begin a formal review — rather than request revisions mid-process — has raised eyebrows among public health experts. Bruce Y Lee, a professor of health policy and management at the CUNY Graduate School of Public Health and Health Policy, said that without clearer feedback, companies are left navigating in the dark.

“If there are things that need scrutiny, a review process can address them. At the end of the review, they can identify the issues that need to be corrected. That gives the company an opportunity to make changes and adapt. When that guidance isn’t provided, it makes it very difficult for someone submitting materials to know how to proceed,” Lee told Al Jazeera.

Moderna has previously reported that its mRNA-1010 vaccine showed 26.6 percent greater effectiveness than an approved annual flu shot from GlaxoSmithKline. The company argues that its study design had been discussed with the FDA’s Center for Biologics Evaluation and Research before the trial began.

“It should not be controversial to conduct a comprehensive review of a flu vaccine submission that uses an FDA-approved vaccine as a comparator in a study that was discussed and agreed on with CBER prior to starting,” Bancel said.

For now, the regulatory pathway appears stalled. William Soliman, CEO of the Accreditation Council for Medical Affairs, said that in situations like this, companies typically revise and resubmit.

“They [Moderna] would have to provide additional analysis or alter the study design and resubmit it for review. That’s typically how it works: they go back, address whatever the FDA is requesting, and then resubmit,” Soliman told Al Jazeera.

This is not Moderna’s first adjustment in the influenza space. In 2025, the company withdrew its application for a combined flu and COVID vaccine to wait for efficacy data from a late-stage influenza trial. Meanwhile, the standalone flu vaccine remains under review in the European Union, Canada and Australia, with potential approvals expected in late 2026 or early 2027.

The timing of the FDA’s decision is also drawing attention. It comes amid broader scrutiny over vaccine policy shifts in Washington. In August, the Department of Health and Human Services — which oversees the FDA — announced plans to scale down mRNA vaccine development.

That broader context is fueling speculation about whether the decision reflects purely scientific judgment or something more. Lee pointed to the atmosphere surrounding recent policy changes.

“A big question is whether this is part of some type of political agenda. Many of the policies and decisions we’ve seen have been rolling back vaccine policies long supported by the science, again without clear explanation why, so the concern is that this is part of a larger trend,” he said.

Healthcare publication Stat News reported that career scientists at the FDA, including the head of its vaccine office, David Kaslow, were prepared to review the application but were overridden by FDA Commissioner Vinay Prasad. The agency has disputed that claim. The Department of Health and Human Services did not respond to Al Jazeera’s request for comment, and the reporting has not been independently verified.