Moderna Inc. disclosed on Feb. 18 that the FDA has accepted its application to review an experimental flu vaccine, setting an action date of August for a potential approval decision.

The biotech company based in Cambridge, Massachusetts, had faced a setback just days earlier when the FDA refused to file the application. Officials cited flaws in the research design, particularly the choice of control vaccine used in trials involving adults over 65. The study enrolled about 41,000 participants and cost Moderna hundreds of millions of dollars, backed by a $750 million investment from Blackstone.

In a statement, Moderna said it resubmitted the application by splitting it into two tracks: traditional approval for adults aged 50 to 64, and accelerated approval for those 65 and older. The company committed to an additional post-market study in the older group if the vaccine wins authorization.

Dr. Vinay Prasad, the FDA’s top vaccine official, signed the initial rejection letter despite objections from the agency’s second-highest-ranking vaccine scientist. Prasad questioned the comparator vaccine’s adequacy against the best available options for seniors.

The turnabout came after talks between Moderna and FDA staff. If approved, the vaccine could reach older adults in time for the flu season starting later this year. It relies on messenger RNA technology, the same platform that powered Moderna’s successful COVID-19 shots.

Health Secretary Robert F. Kennedy Jr. has repeatedly called mRNA vaccines unsafe and ineffective. His influence has led to sharp cutbacks in federal support for such technologies over the past year. Hundreds of millions in research contracts have been canceled, and recommendations for COVID-19 boosters now target narrow groups.

At a PhRMA event in Washington on Feb. 17, FDA Commissioner Dr. Marty Makary addressed the rejection briefly. “You should know the exact details of the trial results, which are public information,” he told moderators during a fireside chat. Makary also defended recent reductions in recommended childhood vaccines, arguing the changes build public trust. “I want to see more kids get vaccinated,” he added.

Moderna CEO Stephane Bancel raised alarms about regulatory uncertainty during the company’s Feb. 13 earnings call. “The current uncertainty in the U.S. FDA regulatory environment creates real challenges for businesses, patients and the broader innovation ecosystem,” Bancel told analysts.

Elsewhere, regulators in Europe, Canada and Australia are evaluating the same vaccine. Public health experts maintain mRNA technology is generally safe, pointing to its track record with COVID-19 vaccines developed during the first Trump administration.

The FDA’s pivot highlights tensions in the vaccine approval process amid shifting federal priorities. Moderna, which reported strong COVID vaccine sales in recent quarters, views flu shots as a key growth area. Approval would mark the company’s first influenza product.