Moderna's effort to revolutionize seasonal flu protection is facing a major setback, after the Food and Drug Administration (FDA) issued a rare "refuse to file" letter for its highly anticipated mRNA vaccine candidate.
The Food and Drug Administration has taken the unusual step of refusing to review Moderna's application for its first mRNA-based seasonal flu vaccine. The agency says the company's clinical studies did not use the most effective "standard of care" vaccines as a comparison for participants over 65.
While Moderna claims that the FDA had previously approved the study design, officials from the Department of Health and Human Services (HHS) argue that the company bypassed 2024 guidelines for testing against high doses recommended by the Centers for Disease Control and Prevention (CDC).
This “refuse-to-file” action is extremely rare — it occurs in about 4% of applications — and in effect blocks the launch in the US of a technology that aims to be produced faster and more accurately than traditional flu vaccines.
The decision has highlighted significant infighting within the FDA's vaccine office. According to reports, Dr. David Kaslow, head of the vaccine division, disagreed with the rejection and refused to sign the official letter, forcing the agency's director of biologics to sign it himself — an unusual step.
This regulatory impasse comes in a changing political climate, as the current administration has recently pulled funding for several mRNA projects. Although the FDA maintains that political leaders did not interfere with this specific decision, the setback delays Moderna’s plans for a combined COVID-19 and flu vaccine in the U.S. In response, Moderna expects to receive the first approvals for the technology from European regulators this year.
