More than nine in 10 adults in the UK are likely to have Covid-19 antibodies, with levels continuing to increase in all nations and regions, new figures show.
However the rate of increase is starting to show signs of slowing down.
The presence of antibodies suggests someone has had the infection in the past or has been vaccinated. It takes between two and three weeks after infection or vaccination for the body to make enough antibodies to fight the virus.
They then remain in the blood at low levels, although these can decline over time to the point that tests can no longer detect them.
The latest estimates from the Office for National Statistics (ONS) are based on a sample of blood test results for the week beginning 12 July.
They show that in England an estimated 93.6 per cent of adults are likely to have Covid-19 antibodies, up from 89.1 per cent a month ago.
This is the smallest month-on-month increase since early January.
In Wales, the estimate is up from 90.3 per cent to 93.2 per cent, while in Northern Ireland it is up from 87.1 per cent to 90.7 per cent. For Scotland the estimate has risen from 84.5 per cent to 92.5 per cent.
The figures for these nations also show signs of levelling off in recent weeks.
The ONS said there is a clear pattern between vaccination and testing positive for Covid-19 antibodies, but “the detection of antibodies alone is not a precise measure of the immunity protection given by vaccination”.
Having antibodies can help to prevent people getting coronavirus again, or if they do get infected, they are less likely to have severe symptoms.
Once infected or vaccinated, the length of time antibodies remain at detectable levels in the blood is not fully known.
The estimated percentage of adults testing positive for antibodies has continued to increase across all regions of England, the ONS said.
For the week beginning 12 July, the estimates range from 91.3 per cent in the North East to 93.9 per cent in London.
The highest percentage continues to be in the older age groups, with the lowest among the youngest groups across the four UK nations.
This reflects the way the vaccination programme was rolled out across the country, with older people offered the jab first.
Some parts of the UK are starting to see a drop in the percentage of people testing positive for antibodies among the oldest age groups, though rates among these groups remain high, the ONS found.
In England an estimated 94.4 per cent of 75 to 79-year-olds had Covid-19 antibodies in the latest week, down slightly from 96.5 per cent a month earlier, while for people aged 80 and over the figure has dropped from 94.2 per cent to 93.6 per cent.
For Wales, the estimate for 75 to 79-year-olds is down from 96.8 per cent to 93.6 per cent, and for over-80s it has dropped from 93.4 per cent to 89.6 per cent.
“Our analysis defines antibody positivity by a fixed amount of antibodies in the blood,” the ONS said. “Most older people who are vaccinated will retain higher antibody levels than prior to vaccination, but may have a lower number of antibodies in the blood at the time of testing.”
Related: Offspring ditch drummer after he refuses Covid vaccine
