The FDA's Skepticism of Moderna's mRNA Flu Vaccine

FDA scientists are questioning the strength of the evidence supporting Moderna’s mRNA flu vaccine, mFlusiva. According to documents filed ahead of an advisory committee meeting, reviewers found gaps in the data that leave the vaccine's effectiveness unclear, particularly for older populations.

The FDA is convening a panel of experts to vote on whether the benefits of the shot outweigh the risks for people between the ages of 50 and 64, or those who are 65 and older. While Moderna reported in the New England Journal of Medicine that its shot reduced the likelihood of flu-like illness by 27% compared to a standard-dose vaccine, FDA staff identified significant limitations in these findings.

The scrutiny centers on three primary evidentiary gaps:

1. Temporal and Viral Breadth: The trial incorporated data from only one flu season. This makes it difficult to predict how the shot will perform against different viral strains in future seasons.
2. Subgroup Uncertainty: There was not a large enough sample size to clearly show if mFlusiva protects against influenza B. Furthermore, Moderna did not definitively prove effectiveness in "very frail" older adults or those with weakened immune systems.
3. Co-administration Data: Reviewers noted a lack of data supporting use in people also receiving vaccines for other respiratory diseases, such as COVID-19.

These limitations reduce the applicability of efficacy data to a substantial portion of the intended patient population.

While staff scientists did not identify major safety concerns, they noted their assessment relied on about six months of follow-up in healthier participants. The agency will need ongoing surveillance to detect rarer side effects that might emerge with broader use.

For Moderna, this meeting is a critical hurdle. The company is seeking approval for a vaccine that U.S. regulators previously refused to review earlier this year. While the FDA does not always follow advisory panel advice, it typically does.

The agency is set to make a decision by Aug. 5. Investors and healthcare providers should watch whether the panel demands more longitudinal data before allowing broad use in high-risk groups.