Johnson & Johnson said it would delay the planned rollout of its Covid-19 vaccine in Europe after US health agencies called for a pause of the jab’s use on Americans while they investigate several incidents of rare blood clots.

In a joint statement on Tuesday, the US Centers for Disease Control and Prevention and the Food and Drug Administration said they were reviewing six reported US cases of “rare and severe” blood clots in individuals who had received the J&J vaccine. The individuals were all women aged between 18 and 48, who developed symptoms six to 13 days after vaccination. 

Peter Marks, the head of the division at the FDA that oversees vaccines, said scientists believed the J&J vaccine was causing similar severe reactions to those experienced by a small number of people who have received the AstraZeneca shot.