The number of people who have antibodies for the virus which causes Covid-19 has increased across the UK, but there is “substantial variation”, new figures show.
Having antibodies in the blood indicates that people have either previously been infected with the virus or have had a Covid-19 vaccine.
The Office for National Statistics (ONS) said that in England an estimated one in five adults would have tested positive for antibodies against the virus on a blood test in the 28 days up to February 1.
Older people were more likely to have antibodies in England.
But in Scotland, Wales and Northern Ireland the highest rates were seen among younger adults.
The increasing number of people with antibodies reflect the effect of the vaccine programme as well as the high levels of infection seen in recent months, the ONS suggested.
Esther Sutherland, principal statistician for the Covid-19 Infection Survey, said: “Antibody positivity rates have increased across all four nations and the effects of the vaccination programmes have begun to appear, especially in the older age groups.
“In England those aged 80 and over currently have the highest percentage of antibody positivity, most likely due to the high vaccination rate in this group.
“In Wales and Scotland those aged 16 to 24 years old have the highest percentage and in Northern Ireland it’s in 25 to 34-year-olds.
“We would expect younger groups to have high levels of antibody positivity after the period of high infection rates we have seen in the last few months.
“We will continue to closely monitor antibodies as the UK vaccination programmes continue to be rolled out.”
The ONS said that there was “substantial variation” in antibody positivity between regions in England.
In London almost one in four people are estimated to have antibodies (24.8%) compared to almost one in eight in the south west (11.6%).
There also appears to be varying rates of antibody positivity in the elderly across the four nations – though the researchers cautioned the figures only relate to those living in private households so will not reflect those in care homes.
In Wales this figure was 12.7% and in Scotland the figure was 11.6%.
The data for Northern Ireland includes those over the age of 70 and 9.1% of this group are estimated to have antibodies for the virus.
The data show that for all age groups
– In England an estimated 18.5% of the population have antibodies, or 8.3 million people over the age of 16.
– In Wales an estimated 14.4% of the population have antibodies, or 365,000 people over the age of 16.
– In Northern Ireland an estimated 13.6% of the population have antibodies, or 201,000 people over the age of 16.
– In Scotland an estimated 11.7% of the population have antibodies, or 521,000 people over the age of 16.