Getting the new mRNA flu shot this season may take some legwork. Moderna's mFlusiva was approved in August for adults 50 and older, months after national pharmacy chains had already ordered their flu vaccine supply. Moderna says it planned a "limited launch in year one" and that the shot is available at more than 13,000 locations, but experts say patients will likely need to use the company's vaccine finder or call pharmacies directly to track it down.
The approval itself came with caveats. The FDA granted traditional approval for adults 50 to 64, but accelerated approval for those 65 and older, with a postmarketing effectiveness study planned. That compromise followed an initial refusal to review the application over concerns that the pivotal trial compared the mRNA shot only with a standard-dose vaccine. A separate phase III study found greater immunogenicity than Fluzone High-Dose in people 65 and up, but it did not measure clinical outcomes. The mRNA shot also produced higher rates of injection-site pain, fatigue, headache, and myalgia, which experts say patients must weigh against the potential added protection.
Experts are split on how to position the vaccine. Amesh Adalja of Johns Hopkins calls Flublok and mFlusiva the two best flu vaccines right now, though he acknowledges there are no good head-to-head studies against enhanced vaccines. William Schaffner of Vanderbilt says the immune response seems superior in some respects, but it remains unclear whether that translates into better protection. He also notes the mRNA platform could eventually allow vaccines to be matched more closely to circulating strains, though that would require the FDA and WHO to adapt their recommendation frameworks. Both experts stress that people should not wait for the ideal shot: flu season has started early, and the advice is to get whatever vaccine is available.