Many millions of people have received the AstraZeneca shot worldwide, including more than 17 million in Britain and the European Union, almost all without serious side effects. In an effort to increase public confidence, many European political leaders have gotten the injections in recent days. The AstraZeneca vaccine has also been administered in the past week to leaders in South Korea, Taiwan and Thailand.
“When you get the call, get the jab,” the British health secretary, Matt Hancock, urged on Monday. More than 11 million AstraZeneca doses have been administered in Britain, almost all of them without serious side effects, and the vaccination campaign has reduced hospitalizations and helped the country to emerge from a dreadful wintertime wave of infections.
Even if AstraZeneca persuades American regulators to authorize its vaccine, it is not clear whether the Biden administration will deploy it here. By the end of May, federal officials have said, the three already authorized sets of manufacturers — Pfizer and BioNTech, Moderna, and Johnson & Johnson — will have supplied enough doses to cover all American adults.
The dust-up over the U.S. data is the latest in a series of miscues and communication blunders by AstraZeneca, whose vaccine, developed with the University of Oxford, was once a front-runner in the race for a safe and effective inoculation.
In September, key federal officials, including the F.D.A.’s commissioner at the time, Dr. Stephen Hahn, learned only from the news media that trials of the vaccine were halted globally after a volunteer in Britain developed worrisome neurological symptoms. AstraZeneca officials had been on a conference call with the F.D.A. just a few hours before the news broke, but they neglected to mention the safety issue.
The U.S. trial was paused for nearly seven weeks last fall, in part because AstraZeneca was slow to provide the F.D.A. with evidence that the vaccine had not caused the neurological symptoms. Investigators concluded that the symptoms could not be linked to the vaccine.
Still, the delay left AstraZeneca trailing the three authorized manufacturers.
Sheryl Gay Stolberg and Sheila Kaplan contributed reporting.