FDA rejects Moderna's mRNA flu vaccine over trial flaws and safety concerns

The US Food and Drug Administration (FDA) has rejected Moderna's application for its first mRNA seasonal flu vaccine. The decision follows concerns over trial design and safety monitoring, despite earlier agreements between the company and regulators. Meanwhile, the US government has also pulled back funding for mRNA vaccine research in infectious diseases, scrapping 22 projects worth around $500 million.

The FDA's refusal was confirmed last week in a letter signed by Dr. Vinay Prasad, director of the Center for Biologics Evaluation and Research. The agency argued that Moderna's trial used an inadequate comparator, as the control arm did not meet the 'best-available standard of care' in the US at the time. Specifically, the study compared Moderna's vaccine, VYD2311, to Fluarix—a standard-dose flu vaccine—even though the FDA had initially approved this approach in April 2024.

Moderna's president, Dr. Stephen Hoge, stated that the rejection contradicted earlier feedback from the FDA. The agency had suggested in August 2024 that it would review the filing and address comparator concerns during the process. Now, however, the FDA has also raised issues about monitoring for myocarditis and pericarditis—known risks linked to mRNA Covid vaccines—demanding stricter safety oversight in the trial.

The decision aligns with broader regulatory shifts. Reports indicate the FDA plans to tighten vaccine approval standards moving forward. Separately, the US Department of Health and Human Services (HHS) has withdrawn support for mRNA technology in infectious disease research, cancelling 22 projects totalling roughly $500 million.

Dr. Prasad, a vocal critic of the government's Covid-19 response, has previously claimed that Covid vaccines caused the deaths of 10 children. Moderna now intends to request a meeting with FDA officials to clarify next steps.

The FDA's rejection leaves Moderna's mRNA flu vaccine in limbo, with the company seeking further discussions. Stricter approval criteria and withdrawn government funding signal a tougher regulatory environment for mRNA vaccine development. The outcome may delay or reshape future vaccine projects relying on this technology.