The U.K. authorized a Covid-19 vaccine developed by the University of Oxford and AstraZeneca PLC, opening the door for the rollout of millions of doses in a country where infections have surged amid a more infectious variant of the virus.

The green light represents the third emergency-use approval of a Western-developed vaccine this month and comes as cases rise sharply in the U.S. and Europe. A shot developed by Pfizer Inc. and Germany’s BioNTech SE and one by Moderna Inc. have both been cleared in the U.S. and are being distributed there.

AstraZeneca’s shot—less effective in clinical trials than its rivals’ injections—won’t be available in the U.S. until the Food and Drug Administration reviews large-scale trials still being conducted there and decides to authorize its use.

The U.K. authorization comes as the country battles a new, potentially more contagious variant of the coronavirus. The mutated virus triggered travel bans recently on visitors and goods from Britain, ratcheting up the political urgency for a speedy vaccine rollout here. Pfizer’s shot is already available in the U.K., where Prime Minister Boris Johnson said on Dec. 21 that a half million of the first of a two-dose regimen have been administered.

Dose Destinations

The Covid-19 vaccine developed by the University of Oxford and AstraZeneca is being counted on to help expand inoculations in the developing world.