European and British regulators said on Wednesday the unusual blood clots should be listed as a very rare side effect of the AstraZeneca vaccine for Covid-19.
The European Medicines Agency (EMA) received reports of 169 cases of the rare brain blood clot by early April, after 34 million doses had been administered in the European Economic Area, according to Sabine Straus, chair of the EMA’s safety committee.
The EEA comprises the 27 EU countries plus Iceland, Norway and Liechtenstein.
In comparison, four women out of 10,000 would get a blood clot from taking oral contraception.
In its statement, the EMA said it was reminding health professionals and recipients to remain aware of “the possibility of very rare cases of blood clots combined with low levels of blood platelets occurring within 2 weeks of vaccination”.
The EMA could not list specific risk factors such as age or gender, but most blood clot cases were women under 60.
On the safety side, she said: “Our safety committee… has confirmed that the benefits of the AstraZeneca vaccine in preventing Covid-19 overall outweigh the risks of side effects.”
Ms Cooke added: “This vaccine has proven to be highly effective – it prevents severe disease and hospitalisation, and it is saving lives.”
Ms Cooke said that one “plausible explanation for these rare side effects is an immune response to the vaccine”.
The condition is similar to one seen in people who have been treated with the drug heparin, a blood thinner used to prevent the formation of clots
Now EU health ministers are holding a virtual meeting to discuss the findings.
AstraZeneca has said its own studies have found no higher risk of blood clots in those vaccinated than in the general population.
Meanwhile, the World Health Organisation’s advisory vaccine safety panel said on Wednesday that although a blood clot link was “plausible” it was “not confirmed” and the cases were “very rare” among 200 million people vaccinated with AstraZeneca globally.