Britons aged 18-29 will be offered an alternative to the Oxford-AstraZeneca vaccine where available, government advisors have decided.
Currently, the UK is also rolling out the Pfizer jab, and the first doses of the Moderna vaccine were administered today in Wales.
The decision from the Joint Committee on Vaccination and Immunisation follows a review of the Oxford jab by the Medicines and Healthcare products Regulatory Agency.
At the weekend, it was revealed that 30 people who have had the vaccine in the UK have developed a blood clot, out of a total 18.1 million people who have received it.
The Medicines and Healthcare Products Regulatory Agency (MHRA) confirmed seven of those people had died as of 24 March.
This afternoon, Boris Johnson said the government believes the Oxford/AstraZeneca vaccine is “safe”, telling reporters on a visit to Cornwall: “But the crucial thing for everybody is to listen to what the scientists, the medical experts have to say later on today.”
On the vaccination programme, he added: “You can really start to see some of the benefits of that – it’s pretty clear that the decline in the number of deaths, the decline in the number of hospitalisations is being fuelled, is being assisted, the steepness of that decline is being helped by the roll-out of the vaccines so it’s very important for everybody to continue to get your second jab when you’re asked to come forward for your turn.”
The development comes as the EU’s medicines regulator announced the conclusions of its own review, saying that “unusual blood clots” should be listed as a “very rare” side-effect.