The FDA has approved the first mRNA-based flu vaccine in the United States. Moderna's mFlusiva received full approval on August 5 for adults ages 50 to 64, with accelerated approval for adults 65 and older.

The vaccine builds on the mRNA technology used in COVID-19 shots. In a late-stage trial of 40,805 adults across 11 countries, it was 26.6 percent more effective than a standard flu shot at preventing confirmed influenza-like illness, according to reports. CNN said the shot is now available at more than 13,000 locations across the US.

However, the CDC has not added mFlusiva to its list of recommended flu vaccines. The agency said this month it would maintain last year's endorsements because of "legal uncertainties and inquiries," MedPath reported.

Medical societies are recommending the vaccine as an option for eligible adults, and pharmacies including Walgreens and CVS are offering it to those 50 and older, though supplies are limited.

The delay marks a break from longstanding practice. The vaccine advisory panel was dismissed by Health Secretary Robert F. Kennedy Jr., and a federal judge in March barred the replacement panel from meeting, leaving the CDC's review process stalled.