Britain on Wednesday became the first country in the world to approve a coronavirus vaccine developed by Oxford University and AstraZeneca as it battles a major winter surge driven by a new, highly contagious variant of the virus.
Britain has already ordered 100 million doses of the vaccine, and the government said it had accepted the recommendation from the Medicines and Healthcare products Regulatory Agency (MHRA) to grant emergency authorisation.
The approval is a vindication for a shot seen as essential for mass immunisations in the developing world as well as in Britain, but one that has been dogged by questions about its trial data that make it unlikely to be approved very soon in the European Union or the United States.
"The NHS (National Health Service) will be able to deliver these shots into people's arms at the speed at which it can be manufactured," Health Secretary Matt Hancock told Sky News.
"I am also now, with this approval this morning, highly confident that we can get enough vulnerable people vaccinated by the spring that we can now see our route out of this pandemic."
He said hundreds of thousands of doses would be available to administer in Britain next week.
Prime Minister Boris Johnson called the approval a "triumph for British science".
The vaccine has been found in trials to be less effective than one developed by Pfizer of the United States and BioNTech of Germany but, crucially for countries with more basic health infrastructure, can be stored and transported under normal refrigeration, rather than at -70 degrees Celsius (-94 Fahrenheit).
AstraZeneca said the authorisation was for a two-dose regimen, and Hancock said the MHRA would set out more details on dosing later on Wednesday.
AstraZeneca Chief Executive Pascal Soriot said the vaccine "has been shown to be effective, well-tolerated, simple to administer and is supplied by AstraZeneca at no profit".
He also told BBC radio: "Our belief at this point is that this vaccine should be effective against the (new, more contagious) variant."
AstraZeneca's late-stage trials showed 62% for participants given two full doses several weeks apart - above the 50% usually considered adequate by regulators - but 90% for a smaller sub-group given a half dose and then a full dose.
AstraZeneca did not specify which dose regime had been approved, but researchers said approval was the most important thing.
"To get out of this debacle, there is no alternative to having a significant majority of the population carrying a high level of neutralising antibodies. With today’s announcement that comes within our grasp," said Danny Altmann, a professor of immunology at Imperial College London.
"I suspect this will speed things by several months. An immune population by the spring starts to look feasible."
The pandemic has already killed 1.7 million people around the world, sown chaos through the global economy and upended normal life for billions since it began in Wuhan, China, a year ago.
Britain and South Africa in particular are grappling with new variants of the coronavirus, which the government and scientists say are more contagious. Many countries have responded by banning passenger flights and blocking trade.