Video report by ITV News Science Editor Tom Clarke
Health Secretary Matt Hancock said there was "exciting new data" suggesting that coronavirus vaccines can reduce hospitalisations by more than 80%.
Speaking at a Downing Street press conference, he said that one shot of either the Oxford/AstraZeneca or Pfizer vaccines works against severe infection among over-70s and significantly reduces hospitalisations.
The study, published by Public Health England (PHE) on Monday, also shows that three to four weeks after a single dose of the Pfizer vaccine, deaths in the over-80s are reduced by 83%.
The study, which has yet to be peer-reviewed, included more than 7.5 million people aged 70 and over in England.
"This is extremely good news," Mr Hancock said.
"In fact, the detailed data show that the protection that you get from catching Covid 35 days after a first jab is even slightly better for the Oxford jab than for Pfizer, albeit both results are clearly very strong."
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The results "may also help to explain why the number of Covid admissions to intensive care units among people over 80 in the UK have dropped to single figures in the last couple of weeks", he added.
The study compared the rate of vaccination in people aged over 70 years of age who test positive for Covid-19, compared to those who test negative as well as data for deaths and hospitalisations.
Since January, data has suggested protection against symptomatic Covid, four weeks after the first dose, ranged between 57 and 61% for one dose of Pfizer and between 60 and 73% for the Oxford-AstraZeneca vaccine, PHE said.
The data also shows symptomatic infections in over 70s decreasing from around three weeks after one dose of both vaccines.
England’s deputy chief medical officer Professor Jonathan Van-Tam welcomed new data on vaccines.
He said data on individuals aged 70 and over shows that for both Pfizer and the Oxford/AstraZeneca jabs there is vaccine effectiveness against illness of approximately 60% after one dose.
Data for the Pfizer vaccine shows the likelihood of mortality is reduced by 85% in over-70s, he added.
He told the Downing Street briefing that the data "gives us those first glimpses of how, if we are patient, and we give this vaccine programme time to have its full effect, it is going to hopefully take us into a very different world in the next few months".
Encouraging people to continue to come forward for their first and second doses, he added: “We have to be patient. We have to push on with the vaccine programme.”
Dr Mary Ramsay, PHE Head of Immunisation, said: "This adds to growing evidence showing that the vaccines are working to reduce infections and save lives.
"While there remains much more data to follow, this is encouraging and we are increasingly confident that vaccines are making a real difference.
"It is important to remember that protection is not complete and we don’t yet know how much these vaccines will reduce the risk of you passing COVID-19 onto others.
"Even if you have been vaccinated, it is it is really important that you continue to act like you have the virus, practise good hand hygiene and stay at home.
However, it is unclear whether the Brazil variant has mutated to become resistant to coronavirus vaccines, Dr Susan Hopkins, strategic response director at Public Health England said.
Six cases of the variant have been identified in the UK, however officials have been unable to locate on carrier who has gone under the radar because the person did not complete their test registration card.
The number of people in the UK to have been given a first dose of a Covid-19 vaccine as of Sunday is 20,275,451.