Around half of Britons in most parts of the country have COVID-19 antibodies, new data shows.
In England, some 54.7% of people in private households are likely to have tested positive for the antibodies in the week to 14 March, according to the latest estimates from the Office for National Statistics (ONS).
Regional estimates for the percentage of people with antibodies range from 60% in the North West, to 50.3% in the South East.
However, the figures only include people in private households and not settings such as hospitals and care homes.
The presence of COVID-19 antibodies suggests someone has either had the virus or been vaccinated.
It takes two to three weeks after infection or vaccination for the body to produce enough antibodies to fight off coronavirus.
So far, 30,151,287 people have received a first dose of a COVID-19 vaccine in the UK, and more than 4.3 million confirmed cases of the virus have been reported since the start of the pandemic.
The government has pledged it will have offered all adults a coronavirus jab by the end of July.
Prime Minister Boris Johnson has also set a target to offer a first dose of the vaccine to all 32 million people in the top nine priority groups by 15 April.
The ONS figures also showed that 86% of people aged 80 and over in private households in England are likely to have COVID-19 antibodies.
Since care home residents were also among the first to receive the vaccine, the true figure for antibodies among those aged 80 and over may be different, the ONS said.
In Wales, an estimated 79.2% of people aged 80 and over were likely to have tested positive for antibodies in the week to 14 March, along with 74% of people in Scotland.
In Northern Ireland, the ONS uses different age groups due to smaller sample sizes and estimated that 76.4% of people aged 70 and over were likely to have tested positive for antibodies in this period.
Scotland’s First Minister Nicola Sturgeon warned against complacency despite the ongoing success of the vaccination programme on Tuesday.
Almost 2.5 million people in Scotland have received the first dose of a vaccine, but Mrs Sturgeon said at her daily coronavirus briefing people should still be "hyper-vigilant".
"There are still no grounds for complacency," she said.
"In fact, it is really important right now that while the vaccination programme continues to be rolled out, that all of us remain hyper-vigilant in how we’re going about our daily lives."