The shot, named mFlusiva, is intended for adults age 50 or older. While there already are multiple flu vaccine options in the U.S., including three specifically recommended for people age 65 or older, tens of thousands of Americans die from influenza every year and older adults are among the most vulnerable. Flu vaccines must be updated annually to best match circulating strains of the virus. Moderna's data showed no major safety issues although the shot did cause some temporary reactions including injection site pain, fever, headache, tiredness and aches that occurred somewhat more than with today's flu shots. The FDA action comes after a highly unusual public dispute over mFlusiva earlier this year.