A trial of the Oxford-AstraZeneca coronavirus vaccine on children has been paused while the UK’s medicines regulator investigates a possible link with rare blood clots in adults.
Prof Andrew Pollard from the University of Oxford told the BBC there were no safety concerns with the trial itself, but its scientists were waiting for further information.
Around 300 volunteers signed up.
Earlier, Boris Johnson said people should get their jab when invited.
The trial, which started in February, is assessing whether the jab produces a strong immune response in children aged between six and 17.
Participants are advised to continue to attend all scheduled visits and can contact the trial sites if they have any questions.
Updates from the European Medicines Agency and the UK’s regulator, the Medicines and Healthcare Products Regulatory Agency (MHRA), are expected in the coming days.