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.

Moderna said mNEXSPIKE was approved by the FDA for use in adults aged 65 and up, as well as some individuals aged 12 to 64.