LONDON — Britain said on Wednesday that it would curb the use of AstraZeneca’s vaccine in adults under 30 because of the risk of rare blood clots, a blow to the efforts of scores of countries reliant on the vaccine to stamp out the coronavirus pandemic amid a global surge in cases.
Adding to the unease, the European Medicines Agency outlined a “possible link” between the vaccine and rare clots, even as it said that Covid-19 remained the far greater threat, leaving decisions about how to use the vaccine in the hands of the 27 member states of the European Union.
Taken together, the decisions represented a considerable setback for the AstraZeneca shot, which has been seen as the principal weapon in the battle to reduce deaths in the vaccine-starved global south.
The world’s most widely administered coronavirus vaccine, it is far less expensive and easier to store than some of the alternatives, spurring its use in at least 111 countries, rich and poor. AstraZeneca, based in Britain, has promised to deliver three billion doses this year, enough to inoculate nearly one in five people worldwide.
Cameroon and the Democratic Republic of Congo have already delayed injections of AstraZeneca’s vaccine amid mounting concerns in Europe. Any further hesitation, scientists said, could cost lives.
“In developing countries, the dynamic is to either use the vaccine you have, or you have nothing,” said Penny Ward, a visiting professor in pharmaceutical medicine at King’s College London. “In which case, carnage ensues.”
For the vast majority of people, British and European regulators said on Wednesday, the benefits of AstraZeneca’s shot far outweigh the risks. The clotting problems were appearing at a rate of roughly one in 100,000 recipients across Europe. Meanwhile, in Britain, the vaccine has driven down hospitalizations from Covid-19 — which can, itself, cause serious clotting problems — and saved thousands of lives, regulators said.
most people doubted the vaccine’s safety.
Over all, use of the shot has suffered: Across Europe, 64 percent of delivered doses of AstraZeneca’s vaccine have been injected into people’s arms, markedly lower than the rates for other shots.
“One hoped there would have been collaboration, and more discussion, between regulators, instead of lots of different countries going off in all sorts of directions,” Professor Ward said. “That aspect has really been the most unhelpful.”