A British trial of the AstraZeneca coronavirus vaccine on children has been paused while regulators assess its possible link to blood clots, the University of Oxford, which helped to develop the drug, said on Tuesday.
The university said there were no safety concerns in the clinical trial but it would await information from the UK's Medicines and Healthcare Products Regulatory Agency on rare cases of blot clots that have been reported in adults before proceeding.
"Parents and children should continue to attend all scheduled visits and can contact the trial sites if they have any questions," Oxford said.
The British agency is one of many bodies across the globe analysing real-world data on the AstraZeneca vaccine to see if there were a definitive link between it and a rare form of blood clot.
Cases were initially reported in Norway and continental Europe.
The WHO and the European Medicines Agency will reveal their findings later this week.
It is the latest drama to hit AstraZeneca, which has been embroiled in controversy over its failure to deliver promised doses to the EU, and over the vaccine's efficacy and safety profile.
The British regulator reported over the weekend that there had been 30 blood-clotting cases, seven fatal, of the 18 million doses administered in the UK.
The European agency said on Tuesday that it "has not yet reached a conclusion and the review is ongoing".
EU Health Commissioner Stella Kyriakides later said the agency was expected to make its decision late on Wednesday.
Ms Kyriakides said she was in "close contact" with the European regulator.
Its head of vaccine strategy, Marco Cavaleri, earlier said there was a clear connection between the vaccine and clots, and that the agency would announce it within hours.
"In my opinion we can say it now: it is clear there is a link with the vaccine," Mr Cavaleri told Italy's Il Messaggero newspaper.
"But we still do not know what causes this reaction."