From the Telegraph paper a major study finds that a single dose stops 2/3 of onward infection, with no hospitalisations recorded.
The data, released on Tuesday night, also revealed that the first jab prevents 100 per cent of hospitalisations after 22 days once an immune response has had time to develop.
It came as the number of vaccine doses administered in the UK passed 10 million, with 9,646,715 first doses and 496,796 second doses.
The number of Covid cases on Tuesday was at an eight-week low of 16,840. There were 1,449 further deaths, but the rolling seven-day total is down nearly 10 per cent.
A Whitehall source said: “These findings are exactly what we need. The finding on hospitalisations is particularly significant. At the moment, we have got restrictions in place to stop people dying and to prevent the NHS keeling over.
“Once you have protected these groups, even if there is some transmission it’s a manageable problem – so we don’t need the restrictions. It’s looking good for schools returning in March, shops reopening in April.”
Published as a pre-print in the Lancet, the figures from the Oxford trial in the UK, South Africa and Brazil suggested the vaccine reduces transmission by 67 per cent after the first jab.
Until now, whether vaccines can prevent transmission has not been confirmed. It is seen as key to lifting restrictions because it means those who have been vaccinated cannot infect those who are yet to receive the jab.
The former Conservative leader Sir Iain Duncan Smith said: “This is very significant and has a positive effect on coming out of lockdown as soon as possible. We have a chance to get the economy moving again quickly.”
Sir Iain added that he expected ministers to respond to the news by speeding up plans to lift restrictions, saying: “It paves the way for the Government to get kids back to school and reopening the economy.”
A senior Government source insisted no virus restrictions could be lifted before the current earliest date of March 8. If all over-70s have been vaccinated by the target date of February 15, they will have developed immunity three weeks later.
The source said: “We hope it will be safe to commence the reopening of schools from March 8, with other economic and social restrictions being removed thereafter as and when the data permits.”
The study found that a single dose was 76 per cent effective in fending off infection between 22 days and 90 days post-injection, rising to 82.4 per cent after a second dose at that stage. In a cohort of 12,408 people vaccinated with the first dose, not one was hospitalised during the period.
In a major vinciation of Government policy, the study also found that the vaccine is more effective overall if the second dose is delayed from 28 days until 90 days.
The delay to the second jab had been criticised by European leaders amid a row over vaccine supply.
On Tuesday, Ursula von der Leyen, the European Commission president,accused ministers of compromising safety, while on Monday Clement Beaune, France’s Europe minister, said Britain had taken “a lot of risks” by choosing to delay the second dose.
Professor Andrew Pollard, the chief investigator of the Oxford Vaccine Trial and study co-author, said the data “supports the policy recommendation made by the joint committee on vaccination and immunisation (JCVI) for a 12-week prime-boost interval, as they look for the optimal approach to rollout, and reassures us that people are protected from 22 days after a single dose of the vaccine”.
Matt Hancock, the Health Secretary, welcomed the findings, saying: “This is a hugely encouraging study and further reinforces our confidence that vaccines are capable of reducing transmission and protecting people from this awful disease.
“This report shows the Oxford vaccine works, and works well. More than 9.6 million people have already received the first dose of their Covid-19 vaccine, and the NHS is working tirelessly to vaccinate as many people as possible in every part of the UK.”
Doubt had also been cast in Europe over the efficacy of the vaccine for over-65s. On Tuesday, the French health authority followed the Germans in recommending the AstraZeneca vaccine only to those aged under 65, despite the European Medicines Agency approving it for all adults.
Although 5.7 per cent of the participants in the Oxford vaccine study were over 70, no one over age of 56 was assessed up to the 12-week stage.
However, the results showed that, for over-55s, the vaccine was 16 per cent more effective at six to eight weeks compared with at three weeks, which might indicate that it continued to build immunity as time went on, in common with younger participants.
In further good news on Tuesday, a Government-sponsored study of people who caught Covid in the first wave revealed that 88 per cent retained antibodies that fight off infection for at least six months.
However, the promising results followed the revelation that Covid in the UK is beginning to mimic the more worrying elements of the South African variant of the virus.
Public Health England has detected dozens of cases with an “E484K” mutation to the spike protein, similar to the South African variant, which is expected to render current vaccines less effective. Studies have indicated that the current crop of vaccines are only 60 per cent effective against the South African variant because of the mutation.
On Tuesday, Mr Hancock said the Government was working closely with pharmaceutical companies to engineer modifications to current vaccines.
Researchers said a “booster” jab to protect the population from emerging strains could be developed in weeks and rolled out in months, raising the prospect that a third dose could be rolled out later this year.
Professor Robin Shattock, who is leading Covid vaccine research at Imperial College London, suggested jabs would be likely to be given in addition to the current two-dose strategy as “an annual booster” after the first programme is rolled out.
Meanwhile, a small study from Cambridge University suggested that elderly people could be left vulnerable to new variants after one dose of the Pfizer jab.
The research, which included 15 people over the age of 80, found one dose was not enough to protect them against a mutated strain. However, it found that the vaccine developed by Pfizer and BioNTech appears to be effective against the Kent variant.