Coronavirus (COVID-19): ONS Infection Survey - headline results - 4 December 2020

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 (22 to 28 November), the percentage of the population in Scotland that had the coronavirus (COVID-19) was 0.78%. A 95% credible interval for this figure is 0.60% to 0.98%.

In the same week, it is estimated that at any given time 40,900 people in Scotland had the coronavirus (COVID-19). A 95% credible interval for this figure is 31,500 to 51,800.  This equates to around 1 in 130 people (95% credible interval: 1 in 165 to 1 in 100). The ratios presented are rounded to the nearest 5.

Modelled estimates suggest that there are early signs that the proportion of people in Scotland that had the coronavirus (COVID-19) has started to decrease.

In the latest six-week period, there were 34,836 swab tests, with a total of 244 positive tests in 169 people from 129 households. In the latest two-week period, there were 13,191 swab tests, and a total of 103 positive tests, in 91 people from 68 households.

Figure 1: Modelled estimates of the percentage of the population in Scotland testing positive for the coronavirus (COVID-19) between 18 October and 28 November, including 95% credible intervals (see notes 1,2,3,4,5,6)

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 2: 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 18 October and 28 November (See notes 1,4,5,6,7,8)

Table 1: Modelled estimates, and corresponding 95% credible intervals, for the most recent week (22 to 28 November) 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	0.96% (0.90% to 1.01%)	521,300 (490,600 to 552,600)	1 in 105 (1 in 110 to 1 in 100)
Northern Ireland	0.52% (0.33% to 0.77%)	9,500 (6,000 to 14,100)	1 in 190 (1 in 305 to 1 in 130)
Scotland	0.78% (0.60% to 0.98 %)	40,900 (31,500 to 51,800)	1 in 130 (1 in 165 to 1 in 100)
Wales	0.60% (0.40% to 0.84%)	18,100 (12,100 to 25,500)	1 in 170 (1 in 250 to 1 in 120)

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 (15 to 28 November), the percentage of the population in Scotland that would have tested positive for the coronavirus (COVID-19) was 1.10%. A 95% confidence interval for this figure is 0.87% to 1.37%. 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 57,800 people in Scotland would have tested positive for the coronavirus (COVID-19) at any given time. A 95% confidence interval for this figure is 45,600 to 72,200. This equates to around 1 in 90 people (95% confidence interval: 1 in 115 to 1 in 75). The ratios presented are rounded to the nearest 5.

Figure 3: Weighed estimates of the percentage of the population in Scotland that would have tested positive for the coronavirus (COVID-19) by non-overlapping 14-day periods between 20 September and 28 November 2020, including 95% confidence intervals (see notes 1,5,9,10,11)

Quality and methodology information

Fieldwork in Scotland is being scaled up with the aim of testing 15,000 participants per fortnightly period. This will enable 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.

An estimate of the proportion of people in Scotland who would have tested positive for COVID-19 antibodies in October was published on the 24 November 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.

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:

• Welsh Government
• Department of Health in Northern Ireland

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 25 November (as marked by the dashed vertical line), as lab results for this period are still being processed at the time of publication.
5. Modelled estimates are not directly comparable with the 14 day weighted estimates.
6. 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.
7. The lines represent the modelled trends for each of the four nations based on the latest data.
8. Credible intervals have not been included in this chart.
9. 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.
10. 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.
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.