The Covid-19 vaccines being used in the UK could reduce a person’s risk of being admitted to hospital by as much as 94% four weeks after the first dose, new data suggests.

Four weeks after receiving the initial dose, the Oxford jab appeared to reduce a person’s risk of hospital admission by up to 94%, according to new research from Scotland.

Sir Patrick Vallance, the Government’s chief scientific adviser, said that it is “clear that AstraZeneca works and it works in older people”.

People who received the Pfizer jab had a reduction in risk of up to 85% between 28 and 34 days after the first dose.

Data for the two jabs combined showed that among people over the age of 80 – who are at high risk of severe disease – the reduction in risk of hospital admission was 81% four weeks after the first dose.

The majority of older people in the study – who are among those at highest risk of severe disease and death from Covid-19 – were more likely to have had the AstraZeneca jab.

Experts examined Covid-19 hospital admissions in Scotland among people who have had their first jab and compared them to those who had not yet received a vaccine.

Scientists from the universities of Edinburgh, Strathclyde, Aberdeen, Glasgow and St Andrews and Public Health Scotland (PHS) looked at data on people who had received either the Pfizer/BioNTech jab or the one developed by scientists at the University of Oxford with AstraZeneca.

Scientists said the evidence showed the vaccines were “performing incredibly well” and that they would anticipate seeing similar results around the UK.

But they said that the study did not set out to examine the differences between the two jabs, and stressed that a comparison would not be “fair” because the vaccines had been offered to different populations.

Lead researcher Professor Aziz Sheikh, director of the University of Edinburgh’s Usher Institute, said: “These results are very encouraging and have given us great reasons to be optimistic for the future.

“We now have national evidence – across an entire country – that vaccination provides protection against Covid-19 hospitalisations.”

He added: “We are overall very, vey impressed with both these vaccines.

“When we move beyond trial circumstances you never know what the results are going to be, but this is out in the field and both are performing incredibly well.”

He said that AstraZeneca had “predominantly” been given to the elderly, adding: “At the moment, we don’t have the numbers to do these age-stratified analyses by different vaccine types but we will have those soon.

“But both of these (vaccines) are working spectacularly well, that said, we haven’t done a direct comparison between the two at the moment.”

Sir Patrick said the Scottish study was “very encouraging”.

But he warned that the estimates have “confidence intervals” – which means that the actual figure may be more or less effective than the one reported – but he added: “But AZ works, and it works in older people.”

Professor Dame Angela McLean, chief scientific adviser for the Ministry of Defence, added: “94 is a very encouraging number , However 94 is not 100. We have to live with that and that’s why getting coverage really, really high, is so important.”

The researchers examined data between December 8 and February 15. During this period, 1.14 million vaccines were administered in Scotland – 21% of the Scottish population.

The Pfizer vaccine has been received by some 650,000 people, while 490,000 have had the Oxford/AstraZeneca vaccine.

Researchers looked at GP records on vaccination, hospital admissions, death registrations and laboratory test results – and compared the outcomes of those who had received their first jab with those who had not.

Dr Teresa Lambe, associate professor at the University of Oxford, said: “When we first started this journey, we could only hope that a year later, real world data would show this level of impact from our vaccine against hospitalisation from severe illness.

“It is a huge day for us all, especially the team who’ve worked so hard, and monumental in our battle against coronavirus.”

Professor Andrew Pollard, chief investigator on the Oxford vaccine trial, said: “We are delighted to see that the real-world evidence reported today from the University of Edinburgh which confirms that both the Oxford-AstraZeneca vaccine and the Pfizer vaccine have a very substantial impact against hospitalisation with Covid-19 disease.

“Vaccines work. We now need to make sure that everyone everywhere is protected.”

Dr Jim McMenamin, national Covid-19 incident director at PHS, said: “Across the Scottish population the results show a substantial effect on reducing the risk of admission to hospital from a single dose of vaccine.

“For anyone offered the vaccine, I encourage them to get vaccinated.”

He said the data was “encouraging” when looking at the effect of vaccination against the UK variant of coronavirus.

Dr McMenamin said that in Scotland, cases of the South Africa variant had “almost exclusively” been linked to travel, adding: “So it is unlikely that we’re able to see anything then about the effect of the vaccine for other variants, but certainly for the UK variant that we have seen across the time period of the study that we’re demonstrating for the whole programme a very encouraging vaccine effect.”

Professor Chris Whitty, chief medical officer for England and co-lead for the National Institute for Health Research (NIHR), said: “This research provides encouraging early data on the impact of vaccination on reducing hospitalisations.”

Chris Robertson, professor of public health epidemiology at the University of Strathclyde, said: “These early national results give a reason to be more optimistic about the control of the epidemic.”

The data has been published as a pre-print.

This means that it is early work that has not yet been through peer-review and has not yet been published in a journal.