Publication - Statistics

Coronavirus (COVID-19): ONS infection survey results - 12 February 2021

Published: 12 Feb 2021

Results from the ONS COVID-19 infection survey from 12 February 2021.

Published:
12 Feb 2021
Coronavirus (COVID-19): ONS infection survey results - 12 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 (31 January to 06 February 2021), the percentage of the population in Scotland that had the coronavirus (COVID-19) was 0.67%. A 95% credible interval for this figure is 0.57% to 0.78%.

In the same week, it is estimated that at any given time 35,400 people in Scotland had the coronavirus (COVID-19). A 95% credible interval for this figure is 30,100 to 41,000.  This equates to around 1 in 150 people (95% credible interval: 1 in 175 to 1 in 130).

Modelled estimates suggest that the percentage of people that had the coronavirus (COVID-19) in Scotland 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 the coronavirus (COVID-19) between 27 December 2020 and 06 February 2021, including 95% credible intervals (see notes 1,2,3,4,5)

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

Between the week ending 30 January and the week ending 6 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 27 December and 06 February, are available on the ONS website.

There is high uncertainty around these estimates due to the relatively smaller 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 1,3,4)

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 6 February 2021. The percentage of people testing positive compatible with the new UK variant has levelled off in the week ending 6 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 27 December 2020 and 06 February 2021 (see notes 1,3,4,10)

*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 27 December 2020 and 06 February 2021 (See notes 1,2,4,5,6)

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 (31 January to 06 February) for the four nations of the UK

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

1.28% (1.21% to 1.34%)

695,400 (660,200 to 732,200)

1 in 80 (1 in 85 to 1 in 75)

Northern Ireland

1.33% (1.08% to 1.61%)

24,400 (19,700 to 29,600)

1 in 75 (1 in 95 to 1 in 60)

Scotland

0.67% (0.57% to 0.78%)

35,400 (30,100 to 41,000)

1 in 150 (1 in 175 to 1 in 130)

Wales

1.16% (0.98% to 1.37%)

35,300 (29,700 to 41,500)

1 in 85 (1 in 100 to 1 in 75)

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 (24 January to 06 February 2021), the percentage of the population in Scotland that would have tested positive for the coronavirus (COVID-19) was 0.92%. A 95% confidence interval for this figure is 0.75% to 1.10%. Averaging estimates of the proportion of people in Scotland that would have tested positive for coronavirus (COVID-19) over the latest 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 48,200 people in Scotland would have tested positive for the coronavirus (COVID-19) at any given time. A 95% confidence interval for this figure is 39,500 to 58,200. This equates to around 1 in 110 people (95% confidence interval: 1 in 135 to 1 in 90).

Figure 5: Weighted estimates of the percentage of the population in Scotland that would have tested positive for the coronavirus (COVID-19) between 20 September 2020 and 06 February 2021, including 95% confidence intervals (see notes 1,5,7,8,9)

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 3 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 75,315 swab tests from 29,164 people, with a total of 612 positive tests in 511 people from 435 households. In the latest two-week period, there were 26,539 swab tests from 18,990 people, with a total of 167 positive tests in 148 people from 118 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. 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.

3. 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. 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.

4. There is more uncertainty around estimates after 03 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.

5. 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.

6. The lines represent the modelled trends for each of the four nations based on the latest data.

7. 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.

8. 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.

9. 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.

10. Small numbers of new UK variant compatible positives detected in Scotland and the other devolved administrations are leading to considerable uncertainty surrounding these estimates.

11. Any ratios presented are rounded to the nearest 5.