Britain's vaccination campaign is slashing Covid-19 infections and the UK has "moved from a pandemic to an endemic situation", scientists said.
A study of more than 370,000 people showed a 65 per cent reduction in infections after one dose of either the Pfizer or AstraZeneca vaccines.
It also showed the vaccines were effective in older people and worked against the UK variant of Covid-19.
Prof Sarah Walker, chief investigator of the National Covid-19 Infection Survey, said the study showed that “the vaccines really do work”.
"We're effectively endemic, we've moved from a pandemic to an endemic situation," she told the Daily Telegraph.
According to the findings, one dose of a vaccine led to a 74 per cent drop in symptomatic cases of Covid-19 and a 57 per cent drop in asymptomatic cases.
After a second dose, protection against symptomatic cases rose to 90 per cent, while overall infections fell by 70 per cent.
Speaking on BBC Radio 4's Today programme, Prof Walker said the vaccines gave Britain an "amazing opportunity" to prevent infections.
“We found that 21 days after a first dose, there was a big, so about two-thirds, reduction in all Covid cases regardless of whether people had had a single dose of the AstraZeneca or the Pfizer vaccine,” she said.
“Vaccination was just as effective in people over 75 and in people who report long-term health conditions.
“That’s important because those people often don’t go into the trials that test the vaccines in the first place.”
The data came from studies by the University of Oxford, the Office of National Statistics and the UK Department of Health.
They analysed more than 1.6 million test results dating back to December when the vaccination campaign began.
Since then, more than 33 million people in Britain have received a first dose of a vaccine, making up 63 per cent of the adult population.
Second doses were administered to more than 11 million people, giving a high level of protection to 21 per cent of adults.
UK studies Covid-19 variants as lockdown is eased
The UK's infection rate fell significantly during a prolonged lockdown that began in January, before restrictions were eased in March and again on April 12.
Prof Walker said it was not possible to assess the effect of the UK's vaccination programme on other variants, such as the strain first identified in South Africa, because there are so few cases of these variants in Britain at the moment, she said.
Testing was ramped up in London this month to rein in the spread of the South African variant after a cluster of cases was found.
Government figures show at least 670 cases of the variant in the UK, as well as 119 cases of two separate strains that were first detected in Brazil.
Scientists in the UK are also studying a new variant detected in India, which is facing a severe crisis in its second wave of the pandemic.
It is not yet clear whether the new variant is more transmissible than other strains or whether it is capable of evading vaccines.
From today, India is on the UK’s travel red list, which means that foreign visitors are banned from entering Britain from India.
UK and Irish citizens and people with residency rights in Britain must stay in government-arranged quarantine hotels if they return from India to the UK.