Around eight in 10 young adults in the UK are now likely to have Covid-19 antibodies, new figures suggest.
The estimates, which are for people aged 16 to 24, range from 80.4% in Northern Ireland to 85.6% in Scotland, with 83.9% for Wales and 85.4% for England.
The presence of coronavirus 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 figures from the Office for National Statistics (ONS) are based on a sample of blood test results for the week beginning August 9.
The estimates are for people in private households and do not include settings such as hospitals and care homes.
They suggest antibody levels among young adults have jumped sharply in recent months, coinciding with the rollout of Covid-19 vaccines to younger age groups.
In England the percentage of 16 to 24-year-olds likely to have Covid-19 antibodies has jumped from 52.9% in the week beginning June 7 to 85.4% in the week beginning August 9, while the estimates for 25 to 34-year-olds have risen from 67.8% to 96.2%.
Scotland has seen particularly sharp increases across the two-month period, with a rise from 40.7% to 85.6% for people aged 16-24 and from 59.7% to 96.2% for 25 to 34-year-olds.
There are signs that antibody levels may be dropping among older age groups, however.
“In some regions and countries, we are starting to see a decline in the percentage of people testing positive for antibodies amongst the oldest age groups, although rates amongst these age groups remain high,” the ONS said.
Levels of antibody positivity are defined by a fixed amount of antibodies in the blood.
“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,” the ONS added.
Overall an estimated 94.1% of the adult population of England was likely to have tested positive for Covid-19 antibodies in the week beginning August 9.
For Wales, the figure is 92.0%, for Scotland 93.6% and for Northern Ireland 90.4%.
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”.
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