The Food and Drug Administration has approved Moderna's new COVID-19 vaccine, days after the federal government tightened vaccine standards for the virus.

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