A single dose of the Covid-19 vaccine offers two thirds protection against the virus, according to reports.
New data on the Pfizer jab is said to show encouraging results in a boost for efforts to vaccinate the nation locked in a race against new variants.
The unpublished findings also reveal the vaccine takes a week longer to become offer protection in older people than it does among younger age groups, The Sun reports.
The data shows that a single jab of the Pfizer vaccine starts to work after 15 days for under-65s but over-80s.
The Oxford AstraZeneca vaccine reportedly offers a similar level of protection against coronavirus.
“One of the key findings is the Pfizer vaccine is having just as big an impact in over-80s as in under-65s," a government source told the publication.
“The only difference is that protection starts after 15 days in younger age groups, but it takes three weeks for it to work in older people.
“These are hugely positive findings, and show vaccination is having a real impact on the pandemic."
The paper said the findings, due to be released in the coming days, will show a reduction in the symptomatic infection risk by 65 per cent in younger adults, and 64 per cent in over-80s.
It was also reported that two shots of the vaccine saw protection levels rise to between 79 and 84 per cent, depending on age.
While declining to comment on leaked figures, a Department for Health spokesperson said: "We continue to be guided by the latest scientific and medical advice as part of a collaborative international effort to tackle this global pandemic and stop the spread of the virus.
"At this stage our absolute focus remains protecting the most vulnerable and ensuring everyone in the first four priority groups are offered a vaccine by mid-February.”
The findings come amid growing concern over the rise of new mutant variants from South Africa and Brazil with the strain first detected in Kent before Christmas now thought to be the dominant variant in the UK.
Experts have also expressed concern that new 'vaccine-busting' variants could emerge that may be more resistant to the jabs.
South Africa has suspended the rollout of the Oxford/AstraZeneca jab after a small study suggested it was less effective against the local strain.
However the UK's Deputy Chief Medical Officer Professor Jonathan Van-Tam moved to reassure the public that the jab is effective against strains circulating in Britain.
The Government has secured access to seven different vaccines, across four different types, totalling over 357 million doses.
This includes 40 million doses of the Pfizer vaccine and 100 million of the Oxford AstraZeneca vaccine.
