The Oxford-AstraZeneca vaccine has been approved for use in the UK, with the first doses due to be given on Monday amid rising coronavirus cases.
The UK has ordered 100 million doses – enough to vaccinate 50 million people.
This will cover the entire population, when combined with the full order of the Pfizer-BioNTech jab, Health Secretary Matt Hancock said.
It comes as millions more people in England are expected to be placed under the toughest tier four restrictions.
On Tuesday, 53,135 new Covid cases were recorded in the UK – the highest single day rise since mass testing began – as well as 414 more deaths within 28 days of a positive test.
Dr June Raine, head of the Medicines and Healthcare Regulatory products Agency (MHRA), said the vaccine would save tens of thousands of lives, adding “no corners have been cut” in assessing the safety and effectiveness of the jab.
Prime Minister Boris Johnson called the vaccine development “a triumph” for British science, adding: “We will now move to vaccinate as many people as quickly as possible.”
And England’s chief medical officer Chris Whitty praised the “considerable collective effort that has brought us to this point”.