The FDA's approval was based on a study of 11,400 people, ages 12 and older, that compared the new low-dose vaccine with Moderna's existing vaccine. It found the new vaccine was safe and was at least as effective -- and more by some measures -- than the original shot, the company said.

The U.S. government has canceled a $600 million contract with Moderna to develop a vaccine for bird flu and other dangerous flu strains, raising concern among experts.

The Trump administration has canceled $766 million awarded to drugmaker Moderna Inc. to develop a vaccine against potential pandemic influenza viruses, including the H5N1 bird flu.