Nearly 90 per cent of adults in England have Covid antibodies, either through vaccination or previous infection, according to new figures.
Public Health England said the Office for National Statistics figures demonstrated that the country was "very close” to achieving herd immunity against the virus in several age groups.
The figures, released on Wednesday, show an estimated 89.8 per cent of those aged 18 and above in England had Covid antibodies in the week beginning June 14.
That is up from the 79.6 per cent reported last month.
The presence of antibodies in the body can mean the human immune system is trained to recognise the virus and fight it.
In England, the highest percentages of antibodies were in those aged between 60 and 64, 70 and 74 and 75 and 79, with an estimated 96.8 per cent testing positive across all the groups.
The lowest coverage was in those aged between 16 and 24, with 59.7 per cent testing positive.
Nine in 10 adults in Northern Ireland and Wales tested positive for Covid antibodies, while Scotland was slightly lower on eight in 10.
Public Health England epidemiologist Meghan Kall said antibody levels in people aged 25 and over were encouraging for achieving herd immunity, when the virus struggles to spread because enough people have already been exposed to the illness through vaccination or previous infection.
"This will be very close to herd immunity levels in these ages", she said on Twitter.
The latest estimates from the ONS are based on a sample of blood test results in private households, which does not include settings such as hospitals and care homes.
It takes between two and three weeks after infection or vaccination for the body to make enough antibodies to fight the infection.
Having antibodies can help to prevent individuals from getting the same infection again, or if they do get infected, they are less likely to have severe symptoms.
However, the ONS said the presence of antibodies does not necessarily mean someone has protection against Covid.
"An immune response does not rely on the presence of antibodies alone", it said.
"We also do not yet know exactly how much antibodies need to rise to give protection. A person's T cell response will provide protection but is not detected by blood tests for antibodies."
The Daily Mail cited sources as saying that Department of Health officials now refer to a strategy of "hybrid immunity", involving vaccinating older, more vulnerable people, combined with a mixture of vaccinations and infections for the young.
On Monday, Prime Minister Boris Johnson stressed that people "must learn to live" with Covid as he announced most lockdown restrictions would be lifted on July 19.
Prof Sir John Bell, an immunologist at the University of Oxford, said the government was banking on the fact most people will not fall seriously ill from the disease after they have been double vaccinated.
"If you’re doubly vaccinated, almost in every age group the likelihood of hospitalisation and death is very small indeed", he told the BBC on Wednesday.
"Our immune responses seem to get better over time. After you’ve had two vaccines, when you pop back up six months later, your immune system has developed a response to the virus to an even more mature state and I think not only do we have good immunity but that immunity may well improve over time."
More than 86 per cent of adults in the UK have received a first dose of a vaccine, while 64 per cent have had two, according to the latest government figures.