Enhanced Surveillance of COVID-19 in Scotland
Population-based seroprevalence surveillance 24 February 2021

About this release

This dashboard release by Public Health Scotland provides the latest results and methodologies of the serology surveillance programme. The serology workstream aims to estimate the proportion of people who have antibodies to coronavirus ("seroprevalence") in the general population of Scotland and to see if this changes over time.

Main points

• The proportion of people attending community healthcare settings who had antibodies to coronavirus is estimated to be 11.2% (95% CI: 9.9%-12.5%) in the 5-week period up to and including week beginning 25 January 2021.
  • At NHS Board level, proportions were highest in NHS Lanarkshire (15.0%, 95% CI: 11.1%-18.7%) and lowest in NHS Shetland (5.8%, 95% CI: 1.2%-12.1%).
  • By age-group, proportions were highest in those aged 0-19 years (13.7%, 95% CI: 11.4%-16.8%) and lowest in those aged 60+ years (8.4%, 95% CI: 6.0%-10.1%).
  • Proportions among males (9.7%, 95% CI: 7.7%-11.1%) were lower than those among females (12.5%, 95% CI: 11.1%-14.8%) in this time period.
    
    
• The proportion of blood donors who had antibodies to coronavirus is estimated to be 12.1% across the 5-week period up to and including week beginning 25 January 2021 (95% CI: 9.9%-14.0%).

Interpretation

• We suggest that, when interpreting the results, there is a focus on the confidence intervals rather than the point estimates.
• This suggests that, overall among those attending community healthcare settings, we can be reasonably confident that COVID-19 seroprevalence lies between 9.9% and 12.5% during the 5-week period up to and including week beginning 25 January 2021. Our results are from a sample of individuals attending community healthcare settings and there is uncertainty whether these individuals are representative of the general population.
• Among blood donors, we can be reasonably confident that COVID-19 seroprevalence lies between 9.9% and 14.0% during the 5-week period up to and including week beginning 25 January 2021. Blood donors tend to be healthier than the general population and, additionally, there are restrictions on blood donations from individuals who have known COVID-19 infection and/or who have symptoms of COVID-19; these estimates may therefore be lower than the general population seroprevalence.

Background

Public Health Scotland (PHS), in partnership with NHS Boards, is leading national surveillance and research studies that include the use of serology (the study of a part of the blood called serum). COVID-19 is caused by the new coronavirus known as SARS-CoV-2. When the body is infected with coronavirus, it produces antibodies to help fight the virus, and these may be detected by blood tests. The detection of antibodies provides an indication that someone has had COVID-19, and provides a way of monitoring what proportion of people have had the virus. We use serology methods to detect these antibodies.

The PHS serology surveillance programme uses existing blood samples within community healthcare and other settings. The serology workstream aims to estimate the proportion of people who have antibodies to coronavirus (“seroprevalence”) in the general population of Scotland and to see if this changes over time.

Since week commencing 20 April 2020, blood samples, originally collected for other clinical reasons in community healthcare settings, have been obtained from regional biochemistry and immunology laboratories across Scotland. Six NHS boards (NHS Grampian, NHS Greater Glasgow & Clyde, NHS Highland, NHS Lanarkshire, NHS Lothian and NHS Tayside) have provided weekly data since the beginning of the programme. An additional five NHS Boards (NHS Dumfries & Galloway, NHS Fife, NHS Forth Valley, NHS Orkney and NHS Shetland) joined the programme at later dates. Approximately 700 samples are collected each week. Laboratories select specific numbers of samples by age and sex to achieve a representative sample based on the age and sex structure of the general population in that NHS board. Samples are anonymised and sent to the Scottish Microbiology Reference Laboratory in Inverness for testing. Seroprevalence rates have been adjusted for the accuracy of the antibody test and weighted to the population structure. The results presented here cover the phase of the project between week commencing 20 April 2020 and week commencing 25 January 2021 (i.e. up to and including 31 January 2021) when 28,219 samples had been received from the 11 participating NHS boards.

Samples originally collected from blood donors have been retrieved and tested by the Scottish National Blood Transfusion Service (SNBTS) since week commencing 29 June 2020. Approximately 500 samples are collected each week from 12 NHS Boards (excluding Shetland and Western Isles). Seroprevalence rates have been adjusted for the accuracy of the antibody test and weighted to the population structure. The results presented here cover the phase of the project between week commencing 29 June 2020 and week commencing 25 January 2021 (i.e. up to and including 31 January 2021) when 15,956 samples had been collected by SNBTS.

Further information

The next release of this publication will be 3 March 2021.