The US FDA refused to review Moderna's application for approval of a new mRNA flu vaccine[1][2][3]. This is because the 40,000-person clinical trial was not "adequately and well-controlled," according to the FDA, because it did not compare the vaccine to the best available standard of care in the US at the time of the study[1][2][3]. The study compared Moderna's vaccine with the standard flu vaccine and found it to be slightly more effective in adults 50 and older[2][3]. The FDA has not raised concerns about the safety or efficacy of the vaccine itself[1]. Moderna said it had previously received positive feedback from the FDA and found the decision surprising[1][2]. The company requested an urgent meeting with the FDA and filed for approval of the vaccine in Europe, Canada and Australia[2]. The decision was signed by the Director of the FDA's Center for Vaccines, Vinay Prasad[1][2].