The first mRNA flu vaccine has been approved by the FDA for adults aged 50 and older, despite earlier setbacks in the approval process. Why the FDA refused to reviewAlthough the vaccine had delivered positive phase 3 trial results – the shot reduced confirmed flu cases by 26.6% compared with a standard-dose flu vaccine – the FDA issued a “refuse-to-file” letter over concerns with the trial design. At issue was Moderna’s choice to use a standard-dose flu vaccine as its benchmark, rather than testing the vaccine against the high-dose formulation typically given to adults over 65. Today’s approval is the result of a U-turn that took place two weeks later, when the FDA reversed course and agreed to review the resubmitted application. Stéphane Bancel, Chief Executive Officer, Moderna, welcomed the decision, saying, “flu remains a significant public health challenge, and mFLUSIVA provides an important new option for America’s seniors”.