The FDA’s decision comes at a time when the number of cases of COVID variant NB.1.8.1 have been rising globally, which according to the World Health Organization, has been detected in 22 countries as of May 18.

The Food and Drug Administration commissioner repeatedly said patients should rely on guidance from their doctors.

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.