The AstraZeneca vaccine trial in children has been paused while an investigation takes place into reports of a rare form of blood clot among adults.
The University of Oxford said that no safety concerns have arisen from the trial itself.
However, it is waiting for more information from the Medicines and Healthcare products Regulatory Agency (MHRA) before giving any more vaccinations.
Data on the jab and its potential association with a rare form of blood clot is being assessed by regulatory bodies from the UK, Europe and the World Health Organisation (WHO).
The WHO and the European Medicines Agency (EMA) have confirmed they will publish findings later this week.
‘No safety concerns in children trial’
The University of Oxford said in a statement: "Whilst there are no safety concerns in the paediatric clinical trial, we await additional information from the MHRA on its review of rare cases of thrombosis/thrombocytopaenia that have been reported in adults, before giving any further vaccinations in the trial.
"Parents and children should continue to attend all scheduled visits and can contact the trial sites if they have any questions."
Professor urges people to continue accepting the vaccine
Professor Calum Semple, a member of the Government's Scientific Advisory Group For Emergencies (Sage), said that the decision was taken out of "exceptional caution" and urged people to continue accepting Oxford/AstraZeneca jabs.
He told Channel 4 News: "This has been done out of exceptional caution and the big story still is that for a middle-aged, slightly overweight man, such as myself, my risk of death is one in 13,000 - the risk of this rare clot, which might not even be associated with the vaccine, is probably one in a million.
"So I'm still going to say it's better to get the vaccine than not get the vaccine and we can pause and take time to carefully consider the value for children because they're not at risk of death from Covid."
He added: "If you've been called for the vaccine then you're in an age group that is very likely to benefit from the vaccine. So the bottom line is if you've been called for the vaccine I would urge you to take the vaccine."
PM urges public to trust the regulator
The Prime Minister earlier urged the public to trust the regulator on vaccine safety.
Boris Johnson said getting the population vaccinated was "the key thing", while he visited the AstraZeneca manufacturing plant in Macclesfield.
"On the Oxford/AstraZeneca vaccine, the best thing people should do is look at what the MHRA (Medicines and Healthcare products Regulatory Agency) say, our independent regulator - that's why we have them, that's why they are independent," he said.
"Their advice to people is to keep going out there, get your jab, get your second jab."
He added: "The best thing of all is to vaccinate our population, get everybody out getting the jab, that's the key thing and that's what I would advocate, number one".