The coronavirus vaccine developed by the University of Oxford stops up to 90% of people getting symptoms, a trial has suggested.
Researchers, who carried out a large-scale trial of 20,000 people in partnership with pharmaceutical company AstraZeneca, say overall the vaccine is 70% effective.
But they added this rose to 90% in a group of volunteers who were given an initial half dose, followed by a full dose.
It is not yet clear why this is the case.
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It comes after vaccines by Pfizer and Moderna were found to give 95% protection.
But the Oxford injection is much cheaper, easier to store and transport around the world as it doesn’t need to be stored at sub-zero temperatures.
The researchers have managed to shorten the normally decade-long process of developing a vaccine to around 10 months.
The Government has pre-ordered 100 million doses of the Oxford vaccine, which would be enough to immunise 50 million people.
Health secretary Matt Hancock called the results ‘really encouraging news’, but stressed vaccines need to be approved by the regulatory body first.
‘This is really encouraging news on the Oxford AstraZeneca vaccine, that obviously we’ve been backing since the start,’ he told Sky News.
‘And I’m really very pleased, really welcome these figures, this data, that show that the vaccine in the right dosage can be up to 90% effective.
‘Of course, it’s vital that the independent regulator, the MHRA, will need to look at the data, will need to check to make sure that it’s effective and safe of course.
‘But we’ve got 100 million doses on order and should all that go well, the bulk of the rollout will be in the new year.’
He added: ‘And of course this vaccine, this homegrown vaccine, is easier to administer as well than the Pfizer vaccine, because it doesn’t need to be stored at minus 70.
‘So having two vaccines that appear to have effectiveness, done right, in the 90% range is really, really good news.’
Half of the volunteers involved were based in the UK, and the other half were in Brazil.
The study saw 30 cases of Covid in people who had two doses of the vaccine, and 101 cases in people who received a dummy injection. Researchers said this works out at 70% protection.
In the UK there are four million doses ready, with another 96 million to be delivered.
But the vaccine will first need to be approved by regulators, who will assess the safety, effectiveness and standards of the vaccine in the next few weeks.
It comes after plans for a mass vaccination programme across the country were revealed last week.
Dozens of mass vaccination sites will be set up across the country in the coming weeks.
GP surgeries are organising the first batch, which will involve using practices, community centres and village halls to administer the jabs to care workers and the elderly as soon as next month.
Then the NHS is establishing a series of much larger venues to inject millions of others once those at the top of the priority list have had the jabs.
It is thought to involve empty Nightingale hospitals, conference centres, sports arenas and drive-through testing centres.
The massive operation will start in the New Year, according to documents seen by the Health Service Journal.
And around 40,000 staff will be hired to help administer the vaccine, including trained medics, nurses, firefighters, police community support officers and even members of the Armed Forces.
NHS England aims to roll out 1 million jabs a day, with those over 80, care home residents and workers receiving the vaccine first.
Over 70s, over 60s, those with underlying conditions and then those over 50 will follow, according to a priority list officially revealed by the Government. The order is yet to be decided for the rest of the population.
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