The FDA's approval was based on a study of 11,400 people age 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. Food and Drug Administration has approved a new lower-dose vaccine for active immunization against COVID-19 caused by severe acute respiratory syndrome coronavirus 2.