The U.S. Food and Drug Administration (FDA) has turned down Moderna’s application to approve a new mRNA flu vaccine. The agency refused to review the data because of how the clinical trials were designed. Moderna compared its new shot to standard flu vaccines, but the FDA argued it should have been measured against shots specifically made for high-risk patients. Moderna’s chief executive noted that the decision was based on this comparison and did not raise any red flags about the vaccine’s safety or how well it works. While the U.S. process is stalled, the vaccine is currently being reviewed for licensing in Canada, Australia, and the European Union.