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”.
‘2021 year of hope and recovery’
Vaccination centres will now start inviting patients to come and get the Oxford-Astra Zeneca vaccine from next week.
It is considered essential because it is easier to store and distribute – it can be kept at normal fridge temperature unlike the Pfizer-BioNTech jab that has to be kept at -70C.
There is also more confidence about supply as it is UK-made, whereas the Pfizer-BioNTech jab has to be shipped in from Belgium.
The hope is around two million patients a week could soon be vaccinated with two vaccines now approved.
British Medical Association GP leader Dr Richard Vautrey said it “should certainly be possible” if there is good supply.
Speaking on BBC Breakfast, Mr Hancock said it marked a “significant moment” in the fight against the virus, adding that “2021 can be a year of hope and recovery because we can see our way out of the pandemic”.
More than 600,000 people in the UK have been vaccinated with the Pfizer-BioNTech jab since Margaret Keenan became the first in the world to be given a Covid vaccine outside of a clinical trials.
Prof Andrew Pollard, director of the Oxford Vaccine Group, told BBC Radio 4’s Today programme the vaccine approval was an “astonishing achievement” in science and clinical research.
But he said there was still “more work to do”, warning: “It’s not over yet.”
“Our colleagues in hospital are facing some real horrors caused by this virus. The next steps are critical,” he said.
Meanwhile, the health secretary has said that more areas will be placed under England’s toughest tier four – “stay at home” – restrictions.
Mr Hancock will set out further details of the changes in the House of Commons later.
He has urged people to “stay in this new year” regardless of what tier their local area is under – in a bid to slow the spread of the virus.
Education Secretary Gavin Williamson will also be making a statement later about the return of schools in England in January.
The new vaccine approval comes after Public Health England said the country was facing “unprecedented” levels of infections, and health officials in parts of Wales, Scotland and the south of England voiced concerns about the increasing pressure on the NHS.
Who will get the vaccine?
Priority groups for immunisation have already been identified, starting with care home residents, the over 80s and health and care workers.
Eventually the programme will see all over 50s and younger adults with health conditions offered one of the jabs.
That is more than 25 million in total.
As well as approval of the Oxford-AstraZeneca vaccine, the government announced the immunisation campaign will now shift to giving as many people as possible their first dose of vaccine with a second dose following within 12 weeks.
When the Pfizer-BioNTech jab started being given the aim was to give the second dose after three weeks.
But based on advice from the Joint Committee on Vaccination and Immunisation the aim now is to give as many vulnerable people some protection from Covid-19 – irrespective of the jab they are given.
Trials showed two full doses of the Pfizer-BioNTech jab were 95% effective at preventing infection, while the Oxford-AstraZeneca one showed 62% effectiveness – although even in cases where people were infected there were no cases of serious illness.
Trials of the Oxford-AstraZeneca vaccine also showed when people were given a half dose then a full dose effectiveness hit 90%.
But there was not enough clear data to approve the half-dose, full-dose idea.
However, unpublished data suggests that leaving a longer gap between the first and second doses increases the overall effectiveness of the jab.
All the vaccines are expected to be equally effective against the new variants of the virus that have emerged.