FDA Reverses Course, Agrees to Review Moderna’s mRNA Flu Vaccine

The FDA’s decision to reverse its "Refusal to File" (RTF) for Moderna’s seasonal influenza vaccine, mRNA-1010, marks a significant and rare regulatory pivot. Typically, an RTF is a major setback for a pharmaceutical company, signaling that an application is fundamentally incomplete or has significant deficiencies that prevent a substantive review. For the FDA to rescind such a decision within a short period suggests that Moderna was able to rapidly address the agency’s concerns—likely related to administrative data or specific assay validations—rather than deep-seated clinical failures. This reversal is a major victory for Moderna, which is under intense pressure to diversify its revenue stream as sales of its COVID-19 vaccine, Spikevax, continue to decline from pandemic peaks.

The vaccine candidate at the center of this review, mRNA-1010, is a quadrivalent vaccine targeting the four influenza strains recommended by the World Health Organization: A/H1N1, A/H3N2, B/Yamagata, and B/Victoria. In clinical trials, mRNA-1010 has demonstrated strong immunogenicity, particularly against Influenza A strains, which are responsible for the majority of flu-related hospitalizations and deaths. While earlier data showed some challenges in achieving non-inferiority against Influenza B strains compared to existing vaccines, Moderna’s subsequent Phase 3 trials and updated formulations appear to have satisfied the regulatory threshold for a formal review. The move to mRNA technology for flu vaccines is seen as a potential game-changer for the industry, offering the ability to manufacture doses much faster than traditional egg-based methods, which require a six-month lead time and are susceptible to "egg-adaptation" mutations that can reduce vaccine efficacy.

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The FDA’s decision to reverse its "Refusal to File" (RTF) for Moderna’s seasonal influenza vaccine, mRNA-1010, marks a significant and rare regulatory pivot.