GENEVA: The World Health Organization expects there will be no reason to change its assessment that the benefits of the AstraZeneca vaccine against COVID-19 outweigh any risks, its regulatory director said on Tuesday.

The WHO is closely studying the latest data alongside European and other regulators, in light of reports of blood clots among people who have been vaccinated, said Rogerio Gaspar, WHO director of regulation and prequalification.

A senior official at Europe's medicines regulator has said there is a clear "association" between AstraZeneca's COVID-19 vaccine and very rare blood clots in the brain, though the direct cause of the clots is still unknown.

The European Medical Agency (EMA) said in a statement after the comments by Marco Cavaleri, chair of its vaccine evaluation team, that it was still conducting a review of the vaccine and expected to announce its findings on Wednesday or Thursday.

Gaspar said the WHO expects to reach a fresh assessment on Wednesday or Thursday, after its own vaccine safety advisory group meets, but does not believe there will be a reason to change its advice that the benefits outweigh any risks.

"What we can say is that the appraisal that we have for the moment - and this is under consideration by the experts - is that the benefits-risk assessment for the vaccine is still largely positive," he told a Geneva news conference.

"We continue to see a number of events that are rare events linking thrombocytopenia to thromboembolic events and those rare events are now being categorised in terms of the diagnostics, in terms of the population, in terms of the distribution within the population," he said.

WHO was in touch with various national and regional expert committees that will decide on the vaccine's regulatory status, Gaspar said.