Wei Shen Lim, chair of the Britain's Joint Committee on Vaccination and Immunisation (JCVI), said that based on the available data and evidence, the committee has advised that it was preferable for adults aged under 30 with no underlying conditions to be offered an alternative to the AstraZeneca vaccine where available.
He said that for younger people, where the risks of hospitalization were much lower, the risk/benefit calculation of the Oxford/AstraZeneca shot meant others vaccines were preferable.
"We are advising a preference for one vaccine over another vaccine for a particular age group, really out of the utmost caution, rather than because we have any serious safety concerns," Lim said at a briefing.
He said people should continue to have a second dose of the AstraZeneca shot if they had received a first dose.
It came after Britain's MHRA medicine regulator identified a possible side-effect from the COVID-19 vaccine developed by Oxford University and AstraZeneca involving rare brain blood clotting.
Chief executive June Raine said that the benefits of the shot outweighed the risks for the vast majority, echoing an update from Europe's medicine regulator also made on Wednesday.