Publication - Statistics

Coronavirus (COVID-19): ONS Infection Survey - headline results - 5 March 2021

Published: 5 Mar 2021

Results from the ONS COVID-19 infection survey from 5 March 2021.

Published:
5 Mar 2021
Coronavirus (COVID-19): ONS Infection Survey - headline results - 5 March 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.

The Office for National Statistics (ONS) publish estimates for England, Wales, Northern Ireland and Scotland on their website.

The underlying data displayed in the charts in this publication is available in the reference tables on the ONS website.

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 (21 to 27 February 2021), the percentage of the population in Scotland that had the coronavirus (COVID-19) was 0.30%. A 95% credible interval for this figure is 0.21% to 0.40%.

In the same week, it is estimated that at any given time 15,600 people in Scotland had COVID-19. A 95% credible interval for this figure is 11,000 to 21,300.  This equates to around 1 in 335 people (95% credible interval: 1 in 480 to 1 in 250).

The percentage of people that had COVID-19 in Scotland has continued to decrease 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 COVID-19 between 17 January and 27 February 2021, including 95% credible intervals (see notes 1,3,4,5,6,7)

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

Between the week ending 20 February and the week ending 27 February 2021, the percentage of people testing positive for COVID-19 continued to decrease across all ages (ages 2 to 80) in Scotland, this includes those of school and higher/ further education age.

Modelled daily estimates of the percentage of the population testing positive for COVID-19 in Scotland by single year of age, between 17 January and 27 February, are available in an interactive visualisation 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. Results are provisional and subject to revision.

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)

The reference day of 17 February has been chosen to represent the week 14 to 20 February 2021 and the reference day of 24 February has been chosen to represent the week 21 to 27 February 2021.

Estimate of the percentage of those testing positive for 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 acroFeatured items ss the UK was produced by Sarah Walker at the University of Oxford.

A new variant of 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 Brazilian and South African variants have 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 these variants 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 trend in the estimated percentage of people testing positive for strains that were compatible with the new UK variant was uncertain in the week ending 27 February 2021. The estimated percentage of people testing positive for strains that were not compatible with the new UK variant and where the virus level was too low for the variant to be identifiable decreased in the week ending 27 February.

Due to the continued decrease in overall percentages testing positive for COVID-19, analysis on the new UK variant will not be included in the next Scottish Government Covid-19 Infection Survey publication. The data will continue to be published in the accompanying dataset on the ONS website. Trends in different variants will continue to be monitored over the coming weeks and the charts will be reintroduced into the publication if there is a variant that appears to be affecting the trends in the percentage of people testing positive for COVID-19.

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 17 January and 27 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 COVID-19 in each of the four nations of the UK  

The percentage of people testing positive for COVID-19 in all four UK nations has continued to decrease in the most recent week.

Figure 4: Modelled estimates of the percentage of the population testing positive for COVID-19 in each of the four nations of the UK, between 17 January and 27 February 2021 including 95% credible intervals (See notes 1,3,4,5,6,13)

Table 1: Modelled estimates of the proportion of the population testing positive for COVID-19, and corresponding 95% credible intervals, between 21 and 27 February 2021 for the four nations of the UK (See notes 1,2,3,4,5,13)

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

0.45% (0.41% to 0.50%)

248,100 (224,900 to 271,700)

1 in 220 (1 in 240 to 1 in 200)

Northern Ireland

0.31% (0.18% to 0.48%)

5,700 (3,300 to 8,900)

1 in 325 (1 in 560 to 1 in 205)

Scotland

0.30% (0.21% to 0.40%)

15,600 (11,000 to 21,300)

1 in 335 (1 in 480 to 1 in 250)

Wales

0.35% (0.24% to 0.49%)

10,600 (7,300 to 14,800)

1 in 285 (1 in 415 to 1 in 205)

Modelled estimates of the percentage of the population testing positive for COVID-19, by COVID-19 Infection Survey Sub-Regions

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 in Scotland see note 12.

This data is shown in Figure 5, and is also available as a dynamic map. (See notes 1,2,4,5,6,12,13).

The modelled estimates for the percentage of the population testing positive for COVID-19 in each sub-region of Scotland varies between 0.17% and 0.31%.

The sub-region in Scotland with the highest modelled estimate of the percentage of people testing positive for COVID-19 was CIS Region 127 (NHS Lanarkshire), at 0.31% (95% credible interval: 0.25% to 0.39%).

The sub-region in Scotland with the lowest modelled estimate was Region 123 (NHS Grampian, NHS Highland, NHS Orkney, NHS Shetland and NHS Western Isles), at 0.17% (95% credible interval: 0.14% to 0.22%).

In the latest week, the percentage of the population testing positive for COVID-19  in four CIS regions in Scotland (123, 124, 126, 128) was under 0.25%. The percentage of the population testing positive for COVID-19 in the other two CIS regions in Scotland (125 and 127) was between 0.25% and 0.50%.

Figure 5: Modelled estimates of the percentage of the population within each CIS sub-region who would have tested positive for COVID-19 in the week 21 to 27 February 2021 in the UK (See notes 1,4,12,13)

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

It is estimated that in the most recent 14-day period (14 to 27 February 2021), the percentage of the population in Scotland that would have tested positive for COVID-19 was 0.46%. A 95% confidence interval for this figure is 0.34% to 0.61%. Averaging estimates of the proportion of people in Scotland that would have tested positive for 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 24,300 people in Scotland would have tested positive for COVID-19 at any given time. A 95% confidence interval for this figure is 17,800 to 32,300. This equates to around 1 in 215 people (95% confidence interval: 1 in 295 to 1 in 165).

The 14-day weighted estimates underpin the modelled estimates and are provided for context. As of next week these will no longer be included in the Scottish Government Covid-19 Infection Survey publication. The data will continue to be published in the accompanying dataset on the ONS website.

Figure 6: Weighted estimates of the percentage of the population in Scotland that would have tested positive for COVID-19 between 27 September 2020 and 27 February 2021, by non-overlapping 14-day periods, 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 2 March 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 83,372 swab tests from 31,350 people, with a total of 531 positive tests in 439 people from 372 households. In the latest two-week period, there were 18,898 swab tests from 15,851 people, with a total of 67 positive tests in 66 people from 57 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 24 February (as shown by the vertical dashed line), 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 is 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 in Scotland, 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

   13. Due to a lab delay Northern Ireland estimates are only available up to 26 February, instead of 27 February as for Scotland, England and Wales.