Publication - Statistics

Coronavirus (COVID-19): ONS infection survey results - 19 February 2021

Published: 19 Feb 2021

Results from the ONS COVID-19 infection survey from 19 February 2021.

Published:
19 Feb 2021
Coronavirus (COVID-19): ONS infection survey results - 19 February 2021

The COVID-19 Infection Survey aims to measure:

  • how many people test positive for COVID-19 infection at a given point in time, regardless of whether they report experiencing coronavirus symptoms
  • the average number of new infections per week over the course of the study
  • the number of people who test positive for antibodies, to indicate how many people are ever likely to have had the infection

More detailed analysis will be available when samples from the survey are large enough.

Modelled estimate of the proportion of the population in Scotland that had the coronavirus (COVID-19)

It is estimated that in the most recent week (06 to 12 February 2021), the percentage of the population in Scotland that had the coronavirus (COVID-19) was 0.55%. A 95% credible interval for this figure is 0.46% to 0.66%.

In the same week, it is estimated that at any given time 29,200 people in Scotland had the coronavirus (COVID-19). A 95% credible interval for this figure is 24,300 to 34,600.  This equates to around 1 in 180 people (95% credible interval: 1 in 215 to 1 in 150).

Modelled estimates suggest that the percentage of people that had the coronavirus (COVID-19) in Scotland decreased in the most recent week, as shown in Figure 1.

Figure 1: Modelled estimates of the percentage of the population in Scotland testing positive for the coronavirus (COVID-19) between 02 January and 12 February 2021, including 95% credible intervals (see notes 1,3,4,5,6,7)

Age analysis of the percentage of people testing positive for the coronavirus COVID-19 in Scotland

Between the week ending 06 February and the week ending 12 February 2021, the percentage of people testing positive for coronavirus (COVID-19) has decreased across all ages (ages 2 to 80) in Scotland.

Modelled daily estimates of the percentage of the population testing positive for COVID-19 in Scotland by single year of age, between 03 January and 12 February, are available on the ONS website.

There is high uncertainty around these estimates due to the relatively small number of people included in this analysis so caution should be taken in interpreting the results.

Figure 2: Modelled estimates of the percentage of the population in Scotland testing positive for COVID-19, by single year of age, including 95% credible intervals (see notes 1,5,6)

Estimate of the percentage of those testing positive for the coronavirus (COVID-19) whose test results were compatible with the new UK variant

The following data should be treated with caution. In particular, there are small numbers of positive test results detected in the survey, leading to considerable uncertainty surrounding these estimates. There are further uncertainties given that not all cases that are positive on the ORF1ab and N genes will be the new variant. Data analysis on the prevalence of the new UK variant of the virus across the UK was produced by Sarah Walker at the University of Oxford.

A new variant of the coronavirus (COVID-19) was identified in the UK in mid-November 2020. The new UK variant of COVID-19 has changes in one of the three genes which coronavirus swab tests detect, known as the S-gene. This means in cases compatible with the new variant, the S-gene is no longer detected by the current test. While there are other reasons why a positive swab test may not detect the S-gene, absence of the S-gene has become a reliable indicator of the new UK variant in COVID-19. However, as the viral load decreases (for example, if someone is near the end of their recovery from the infection), the absence of the S gene is a less reliable indicator of the new UK variant.

In contrast the South African variant has an S-gene that is detectable with the current test and will therefore be included in the “not compatible with new variant” group of COVID-19, where the virus level is high enough to identify this. Which of these types of COVID-19 are compatible with the South African variant cannot be identified from the swab PCR test alone. You can read more about the new UK variant in the blog published by ONS.

This analysis looks at the percentage of positive tests which are compatible with the new UK variant of the virus in Scotland.

Figure 3 shows that the estimated percentage of people testing positive for strains not compatible with the new UK variant and the percentage of people testing positive where the virus was too low for the variant to be identifiable has decreased in the week ending 12 February 2021. The percentage of people testing positive compatible with the new UK variant has likely remained level in the week ending 12 February 2021.

Figure 3: Estimated percentage of the population in Scotland testing positive that are compatible with the new UK variant, not compatible with the new UK variant and other ‘not identifiable’ cases, between 02 January and 12 February 2021 including 95% credible intervals (see notes 1,3,5,6,8)

* New variant compatible positives are defined as those that are positive on the N-gene and ORF1ab-gene, but not the S-gene.

** Positives that are not compatible with the new variant are defined as those that are positive on the S-gene, N-gene and ORF1ab-gene.

*** Positives where levels of the virus in the sample are too low for the variant to be identifiable are defined as those that are positive with all other gene patterns. These definitions apply regardless of cycle threshold (Ct) value.

Modelled estimate of the proportion of the population testing positive for the coronavirus (COVID-19) in each of the four nations of the UK  

Figure 4: Modelled estimates of the percentage of the population testing positive for the coronavirus (COVID-19) in each of the four nations of the UK, between 02 January and 12 February 2021 including 95% credible intervals (See notes 1,3,4,5,6)

Table 1: Modelled estimates of the proportion of the population testing positive for coronavirus (COVID-19), and corresponding 95% credible intervals, for the most recent week (06 February to 12 February) for the four nations of the UK (See notes 1,2,3,4,5)

Nation

Estimated percentage of population that had COVID-19

Estimated number of people who had COVID-19

Estimated ratio of people who had COVID-19

England

0.88% (0.83% to 0.94%)

481,300 (451,600 to 512,400)

1 in 115 (1 in 120 to 1 in 105)

Northern Ireland

0.97% (0.76% to 1.22%)

17,800 (13,900 to 22,400)

1 in 105 (1 in 130 to 1 in 80)

Scotland

0.55% (0.46% to 0.66%)

29,200 (24,300 to 34,600)

1 in 180 (1 in 215 to 1 in 150)

Wales

0.81% (0.66% to 0.97%)

24,600 (20,100 to 29,400)

1 in 125 (1 in 150 to 1 in 105)

Modelled estimates of the percentage of the population in Scotland testing positive for COVID-19, by Coronavirus (COVID-19) Infection Survey Sub-Regions

The first modelled estimates of the percentage of the population testing positive in Scotland by sub-region are now available. ONS have created sub-regions across the UK for the purposes of this survey. In Scotland, these sub-regions are comprised of Health Boards. For a list of sub-regions see note 12.

This data is shown in Figure 5, and is also available as a dynamic map, which can be found here. (See notes 1,2,4,5,6,12).

The ONS modelled estimates for the percentage of the population testing positive in each sub-region of Scotland varies between 0.40% and 0.54%.

Figure 5: Modelled estimates of the percentage of the population within each (numbered) CIS sub-region in Scotland who would have tested positive for COVID-19 in the week 06 to 12 February 2021 (See notes 1,4,12)

This map of Scotland, broken down into sub-regions, shows the percentage of the population in each  sub-region of Scotland who would have tested positive for COVID-19 in the week 06 to 12 February.

The data displayed in the image is available in the table below.

Map Number

Health Boards

Estimated percentage of people testing positive (including 95% credible intervals)

123

NHS Grampian, NHS Highland, NHS Orkney, NHS Shetland and NHS Western Isles

0.40% (0.31% to 0.51%)

124

NHS Fife, NHS Forth Valley and NHS Tayside

0.43% (0.33% to 0.54%)

125

NHS Greater Glasgow & Clyde

0.48% (0.38% to 0.60%)

126

NHS Lothian

0.40% (0.31% to 0.52%)

127

NHS Lanarkshire

0.54% (0.42% to 0.69%)

128

NHS Ayrshire & Arran, NHS Borders and NHS Dumfries & Galloway

0.44% (0.34% to 0.58%)

14-Day weighted estimates of the proportion of the population in Scotland that would have tested positive for the coronavirus (COVID-19)

It is estimated that in the most recent 14-day period (30 January to 12 February 2021), the percentage of the population in Scotland that would have tested positive for the coronavirus (COVID-19) was 0.72%. A 95% confidence interval for this figure is 0.59% to 0.88%. Averaging estimates of the proportion of people in Scotland that would have tested positive for coronavirus (COVID-19) over the past 14-day period can mask changes that have occurred in the most recent week.

In the same 14-day period, it is estimated that an average of 38,000 people in Scotland would have tested positive for the coronavirus (COVID-19) at any given time. A 95% confidence interval for this figure is 30,900 to 46,200. This equates to around 1 in 140 people (95% confidence interval: 1 in 170 to 1 in 115).

Figure 6: Weighted estimates of the percentage of the population in Scotland that would have tested positive for the coronavirus (COVID-19) between 26 September 2020 and 12 February 2021, including 95% confidence intervals (see notes 1,4,9,10,11)

Quality and methodology information

Fieldwork in Scotland has been scaled up to test 15,000 unique participants per fortnightly period. More detailed analysis, such as examining the characteristics of those testing positive for COVID-19 and establishing the average number of new infections per week will be produced when the sample size permits.

The latest estimate of the proportion of people in Scotland who would have tested positive for COVID-19 antibodies was published on 03 February on the Scottish Government and ONS website.

How this data can be used

The data can be used for:

  • estimating the number of current positive cases in the community, including cases where people do not report having any symptoms

The data cannot be used for:

  • measuring the number of cases and infections in care homes, hospitals and other institutional settings
  • estimating the number of positive cases and new infections in smaller geographies, such as towns and cities
  • providing information about recovery time of those infected
  • producing a UK estimate; ONS now have estimates for England, Scotland, Wales and Northern Ireland, but these cannot be added up or averaged to understand the UK infection rate

Methodology

The results are based on nose and throat swabs provided by participants to the study, obtained from fieldwork which started in Scotland on 21 September 2020.

The results are for private households only, and do not apply to those in hospitals, care homes or other institutional settings. The population used in this analysis relates to the community population aged two years and over.

In the latest six-week period, there were 78,339 swab tests from 29,743 people, with a total of 613 positive tests in 510 people from 436 households. In the latest two-week period, there were 24,496 swab tests from 18,811 people, with a total of 138 positive tests in 129 people from 108 households.

The Infection Survey bulletins available on the ONS website also include results for England, Wales and Northern Ireland.

The Welsh Government and the Department of Health in Northern Ireland also publish results from the COVID-19 Infection Survey for Wales and Northern Ireland respectively:

Further details on the methodology used can be found on the ONS website.

Notes

  1. Results are provisional and subject to revision.
  2. Any ratios presented are rounded to the nearest 5.
  3. There is more uncertainty around estimates after 09 February (as shown by the dashed lines), as lab results for this period are still being processed at the time of publication. Additional swab tests that become available after this publication are included in subsequent models, meaning that modelled estimates can change as additional data are included.
  4. Modelled estimates are not directly comparable with the 14-day weighted estimates. The 14-day weighted estimates underpin the modelled estimates and are provided for context.
  5. The model used to provide these estimates is a Bayesian model: these provide 95% credible intervals. A credible interval gives an indication of the uncertainty of an estimate from data analysis. 95% credible intervals are calculated so that there is a 95% probability of the true value lying in the interval.
  6. Because of the relatively small number of tests and a low number of positives in the sample, credible intervals are wide and therefore results should be interpreted with caution.
  7. The blue line and shading represent the modelled trend and credible intervals based on the latest data. The point estimates and error bars represent the official weekly estimates and their credible intervals, which are based on the modelled estimate for the midpoint of the week at the time of publication.
  8. Small numbers of new UK variant compatible positives detected in Scotland and the other devolved administrations are leading to considerable uncertainty surrounding these estimates.
  9. Estimates are weighted to be representative of the population in Scotland that live in private-residential households in terms of age (grouped), sex, and region.
  10. Weighted estimates are provided with 95% confidence intervals to indicate the level of uncertainty around them. A confidence interval gives an indication of the degree of uncertainty of an estimate, showing the precision of a sample estimate. The 95% confidence intervals are calculated so that if we repeated the study many times, 95% of the time the true unknown value would lie between the lower and upper confidence limits. A wider interval indicates more uncertainty in the estimate.
  11. The 14-day non-overlapping time periods presented in this publication are updated to work backwards from the most recent 14 days available. Time periods presented overlap with those presented in previous publications, therefore direct comparisons are not possible.
  12. The table below contains the composition of each CIS region, by Health Board and Local Authority area.

 

CIS Region Code

Health Boards

Local Authority Areas

123

NHS Grampian, NHS Highland, NHS Orkney, NHS Shetland and NHS Western Isles

Aberdeen City, Aberdeenshire, Argyll & Bute, Highland, Moray, Na h-Eileanan Siar, Orkney Islands, Shetland Islands

124

NHS Fife, NHS Forth Valley and NHS Tayside

Angus, Clackmannanshire, Dundee City, Falkirk, Fife, Perth & Kinross, Stirling

125

NHS Greater Glasgow & Clyde

East Dunbartonshire, East Renfrewshire, Glasgow City, Inverclyde, Renfrewshire, West Dunbartonshire

126

NHS Lothian

City of Edinburgh, East Lothian, Midlothian, West Lothian

127

NHS Lanarkshire

North Lanarkshire, South Lanarkshire

128

NHS Ayrshire & Arran, NHS Borders and NHS Dumfries & Galloway

Dumfries & Galloway, East Ayrshire, North Ayrshire, Scottish Borders, South Ayrshire