The US FDA has refused to review Moderna's application for approval of a new flu vaccine[1]. Moderna received a rejection letter in which the regulator called its clinical study inadequate[1]. A study of 40,000 people compared the new vaccine with the commonly used flu vaccine and found it to be slightly more effective in adults 50 and older[1]. The FDA stated that the study did not compare the vaccine to the best available standard of care in the US at the time of the study[1]. Moderna admitted that a different brand of vaccine would be more appropriate for people over 65, but the study was initially approved by the FDA[1]. This move may delay vaccine approval until 2026[1][2].