Moderna's coronavirus vaccine has become the second to be approved for emergency use in the US.
The country's Food and Drug Administration announced the authorisation a day after the agency's panel of outside experts backed the vaccine.
The FDA based its decision on results from a late-stage study of 30,000 volunteers finding the vaccine was nearly 95% effective at preventing illness from COVID-19.
The study also said there were no serious safety concerns resulting from the vaccine's use.
Moderna says it is prepared to distribute 5.9 million shots as early as this weekend.
