The Food and Drug Administration’s refusal to even file Moderna’s application for its first mRNA-based flu shot is more than a bureaucratic hiccup. It is a rare public rebuke of a company that helped define the Covid vaccine era and a signal that the regulatory climate for mRNA is shifting from emergency acceleration to painstaking

The vaccine maker Moderna said on Tuesday that the Food and Drug Administration had notified the company that the agency would not review its mRNA flu vaccine, the latest sign of federal health policy...