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Infection survey data estimate 1 in 8 people already had COVID-19 at the end of 2020

Results from an ongoing infection survey in the UK indicate that in England just over a tenth of the population have already been infected with the virus.

Since May 2020, the Office for National Statistics (ONS) has been conducting a random survey of COVID-19 infection rates in households (excluding people in nursing homes or hospitals). The ONS survey is ongoing and is seeking to monitor the prevalence of COVID-19 infections through collection of nasopharyngeal swabs and blood samples for the detection of COVID-19 antibodies, to provide some insight of the number of individuals who are likely to have previously been exposed to the virus and have thus developed antibodies to it. However, the absence of detectable antibodies does not necessarily mean that someone has not been infected; it may reflect the fact that antibodies titres decline over time and at the present time, precisely how long antibodies last is unknown. The ONS collects data on a monthly basis from more than 20,000 households across England but this has been extended to include, Wales, Scotland and Northern Ireland.

The most recent data is from December 2020 and the ONS estimates, based on the number of positive blood samples, that in England, approximately 5.4 million people (12.1%) aged 16 years and over, or 1 in 8, would have tested positive for COVID-19. This compares to a prevalence of 7.4% collected in the first survey undertaken during May 2020. Thus, a much larger section of the community has been exposed to the virus in the previous 7 months. The ONS data also reveals a large degree of variation between regions in the UK. For example, 16.8% in Yorkshire and The Humber compared with 4.9% in the South West.

For each of the other three nations, the prevalence estimates are all slightly lower than in England, but the ONS makes clear that due to a low positivity rate in the tested samples, there is a much higher level of uncertainty with these estimates as shown by the wide 95% confidence intervals (95% CI). For example, in Wales, an estimated 247,000 (9.8%) of the population, have already had the virus (95% CI, 6.9% to 13.3%). In Northern Ireland, approximately 115,000 (7.8%) people have had the virus (95% CI 3.5% to 14.4%). Finally, for Scotland, approximately 398,000 (8.9%) of people aged 16 years and over (95% CI 7.2% to 10.9%). Despite these uncertainties in the estimates, the data clearly show that in each of the four regions of the UK, the proportion of people with COVID-19 antibodies is at the highest level since recording began.

ONS. Coronavirus (COVID-10) Infection survey: antibody data for the UK, January 2021.