The vaccine, called mFlusiva, was approved for older adults. In trials, it was found to be about 27% more effective than a standard flu shot.

The FDA has approved the first mRNA flu vaccine in the United States after a clinical trial found it was about 27% more effective than a standard flu shot. Manufactured by Moderna and marketed as mFlusiva, the vaccine is expected to be available this fall for adults ages 50 to 64 and those 65 and ol...