Everyone aged under 40 will now be offered either the Pfizer or Moderna jab, following a change in advice from the UK's joint committee on vaccination and immunisation.
Vials labelled "Astra Zeneca COVID-19 Coronavirus Vaccine" and a syringe are seen in front of a displayed AstraZeneca logo, in this illustration photo taken March 14, 2021.
A Department of Health and Social Care spokesman said the position of the MHRA and JCVI "continues to be that the benefits of the Oxford/AstraZeneca vaccine outweigh the risks for the vast majority of adults".
England's Deputy Chief Medical Officer, Jonathan Van-Tam, said the government expects to be able to follow the new advice and still meet its target of giving everyone over 18 a vaccine jab by July 31.
Northern Ireland will face vaccine rollout delays for several weeks as United Kingdom advice regarding the use of AstraZeneca jabs has changed.
Three potential vaccines have emerged as frontrunners in recent weeks. Pic John Cairns University of Oxford PA Wire
In the latest weekly figures, Britain's medicine regulator said that the case incidence of the rare clots and low platelet levels was 10.5 per million doses, compared to 9.3 per million last week.
Those under 40 will no longer receive first doses of the jab due to links with rare blood clots. There were 49 deaths.
According to senior government scientists, this has been one of the hardest decisions they've had to make regarding the vaccine roll-out so far because it's such a finely balanced problem.On the one hand is the evidence of the risks of the vaccine: As more doses have been administered it's become clearer that the risk of the vaccine becomes greater the younger you are.
Commenting on the findings, Paul Hunter, a professor of medicine at Britain's University of East Anglia, said they added to understanding of the risk of thrombosis after Covid-19 vaccination, but should not alter regulators' conclusions.
As India grapples with a deadly surge in its COVID-19 caseload - the country is posting more than 400,000 new cases a day - its government has restricted virtually all exports of Serum Institute-made shots, diverting most of the 2.4 million doses the institute churns out each day to the domestic vaccination campaign.
"If your risk of COVID is moderate to high, get the first vaccine available now", she said.The other parts of the U.K. - Scotland, Wales and Northern Ireland - are following slightly different reopening timelines.