Britain beating the United States to authorization — on a vaccine co-developed by the American pharmaceutical giant Pfizer, no less — may intensify pressure on U.S. regulators, who are already under fire from the White House for not moving faster to get doses to people. And it has stirred up a global debate about how to weigh the desperate need for a vaccine with the imperative of assuring people that it is safe.

No country until Wednesday had authorized a fully tested coronavirus vaccine; Russia and China approved vaccines without waiting for large-scale efficacy tests.

“Help is on its way with this vaccine — and we can now say that with certainty, rather than with all the caveats,” the British health secretary, Matt Hancock, said on Wednesday, as the government exulted in its decision.

While the go-ahead bodes well for Britain, which broke from the European Union’s regulatory orbit to approve the shot early, it will have no effect on the distribution of the hundreds of millions of doses that other wealthy countries have procured in prepaid contracts.