Rome: There is a link between AstraZeneca’s COVID-19 vaccine and very rare blood clots in the brain, but the possible causes are still unknown, a senior official for the European Medicines Agency (EMA) said in an interview published on Tuesday. However, the EMA later said in a statement that its review of the vaccine was on going and it is expected to announce its findings on Wednesday or Thursday.

An AstraZeneca spokesman declined to comment on the matter. “In my opinion, we can now say it: It is clear that there is an association (of the brain blood clots) with the vaccine. However, we still do not know what causes this reaction,” Marco Cavaleri, chair of the vaccine evaulation team at the EMA, told Italian daily Il Messagero. Cavaleri provided no evidence to support his comment.

The World Health Organization has backed the vaccine. AstraZeneca has said its studies have found no higher risk of clots. Some countries, including France, Germany and the Netherlands, have suspending the use of the vaccine in younger people while the investigations continue.