AstraZeneca Vaccine Faces New Setbacks in U.K. and European Union

Britain said it would give alternative shots to people under 30, while the European regulator said it had found a ‘possible link’ with rare blood clots.

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.