The United States has started domestic shipments of the coronavirus vaccine developed by pharmaceutical company Moderna.
Boxes containing vaccine doses were loaded onto trucks at a freezer facility in the southern state of Mississippi on Sunday for distribution across the country.
The vaccine's emergency use was authorized by the Food and Drug Administration on Friday. It is the second coronavirus vaccine to be approved by the regulator, following one jointly developed by US pharmaceutical firm Pfizer and German partner BioNTech.
Moderna's vaccine can be stored at minus 20 degrees Celsius in standard freezers.
That is higher than the roughly minus 70 degrees required to store the Pfizer-BioNTech vaccine.
A government official says Moderna doses are easier to send to small medical institutions and remote areas.
The government is aiming for a total of 20 million doses of the two vaccines to be delivered nationwide through early next month.
People first in line to be vaccinated include medical professionals and elderly residents of care facilities.
Moderna is under contract to supply Japan with doses for 25 million people by September.