New mRNA Flu Vaccine Produced Much Higher Rates of Adverse Reactions Than Standard Shot | 14 Aug 2026 | Moderna’s own clinical trial data raise serious questions about whether the U.S. Food and Drug Administration (FDA) should have approved the company’s new mRNA flu vaccine, medical commentator John Campbell, Ph.D., said. In a recent video, Campbell argued that the study shows only a small reduction in flu cases while reporting substantially higher rates of adverse reactions among people who received the shot. The FDA approved Moderna’s mFlusiva this month for adults ages 50-64, with accelerated approval for adults 65 and older. It is the first mRNA flu vaccine licensed in the U.S. Moderna said it expects the vaccine to be available for the 2026-27 respiratory virus season. Campbell also questioned why the approval came just one year after the U.S. Department of Health and Human Services (HHS) announced a coordinated federal wind-down of mRNA vaccine development.