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 change marks a shift in the Food and Drug Administration’s policy on approving COVID-19 vaccines, which the new commissioner described as a “one-size-fits-all regulatory framework.”