Coronavirus (COVID-19): ONS Infection Survey – headline results – 23 December 2021

ONS Coronavirus (COVID-19) Infection Survey Results 23 December 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 or have been vaccinated

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.

All results are provisional and are subject to revision.

This publication has been brought forward in order to publish before Christmas, and to align with ONS, as a result the release is shorter than usual.

Main Points

In the week 10 to 16 December 2021, the estimated percentage of the population living in private residential households testing positive for COVID-19 in Scotland was 1.45% (95% credible interval: 1.20% to 1.72%). The percentage of people testing positive for COVID-19 in Scotland has increased in the most recent week.

This equates to an estimated 76,200 people living in private residential households in Scotland that had COVID-19 at any given time (95% credible interval: 63,100 to 90,500), or around 1 in 70 people (95% credible interval: 1 in 85 to 1 in 60).

In the week 10 to 16 December 2021, estimates for the other nations of the UK are as follows:

• in England, the trend in the percentage of people testing positive in private residential households increased in the most recent week: 2.21% (95% credible interval: 2.10% to 2.32%).
• in Wales, the trend in the percentage of people testing positive in private residential households was uncertain in the most recent week: 1.79% (95% credible interval: 1.46% to 2.15%).
• in Northern Ireland, the trend in the percentage of people testing positive in private residential households was uncertain in the most recent week: 2.06% (95% credible interval: 1.59% to 2.60%).

In Scotland, the percentage of people testing positive for COVID-19 increased in nursery and primary age children and for those around 40 in recent weeks. The trends are uncertain for all other ages.

In Scotland, the estimated percentage of the population living in private residential households testing positive for Omicron variant compatible cases of COVID-19 has increased in the most recent week (10 to 16 December 2021). The percentage of people testing positive for Delta variant compatible cases has decreased in the most recent two weeks, but the trend is uncertain in the most recent week. There is considerable uncertainty surrounding these estimates by variant due to the small numbers of positives detected in Scotland. This data should be treated with caution.

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

It is estimated that in the most recent week (10 to 16 December 2021), the percentage of those living in private residential households in Scotland that had the coronavirus (COVID-19) was 1.45%. A 95% credible interval for this figure is 1.20% to 1.72% (see note 4 for further information about credible intervals).

In the same week (10 to 16 December 2021), ONS estimate that 76,200 people living in private residential households in Scotland at any given time had COVID-19. A 95% credible interval for this figure is 63,100 to 90,500. This equates to around 1 in 70 people (95% credible interval: 1 in 85 to 1 in 60).

As shown in Figure 1, the percentage of people testing positive for COVID-19 in Scotland has increased in the most recent week.

Modelled daily estimates of the percentage of people testing positive for COVID-19, and accompanying credible intervals, are represented in Figure 1 by the blue line and grey shading. The model smooths the series to understand the trend and is revised each week to incorporate new test results. Modelled daily estimates are used to calculate the official reported estimate and provide the best indication of trends over time.

Official reported estimates of the percentage of people testing positive for COVID-19, are based on the modelled estimate for the midpoint of the most recent week at the time of publication, and represent the best estimate at that point in time. Official reported estimates, and accompanying credible intervals, are represented in Figure 1 and Figure 2 by the point estimates (blue circles). In Figure 2, pale blue circles denote 14-day weighted estimates while the official reported weekly estimates are denoted by dark blue circles.

Figure 1: Modelled daily estimates and official reported estimates of the percentage of the private residential population in Scotland testing positive for COVID-19 between 5 November and 16 December 2021, including 95% credible intervals (see notes 2,3,4,5,6)

Figure 2 shows the trend in the official weekly reported estimates of the percentage of those living in private residential households testing positive for COVID-19 between 3 October 2020 and 16 December 2021. As shown in Figure 2, the estimated percentage of the private residential population testing positive for COVID-19 had been increasing from the middle of August 2021, after weeks of a decreasing trend. The rate of increase then slowed, and the rates were decreasing up to late October. This was followed by a few weeks of fluctuation in estimates. In the most recent week, the percentage of people testing positive for COVID-19 in Scotland has increased. All official reported estimates of positivity displayed in this chart are available in the accompanying dataset on the ONS website.

Figure 2: Official reported estimates of the percentage of the private residential population in Scotland testing positive for COVID-19 between 3 October 2020 and 16 December 2021, including 95% credible intervals (see notes 3,4,5,6,7)

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

Modelled daily estimates of the percentage of the private residential population testing positive for COVID-19 in Scotland by single year of age, are available in an accompanying dataset on the ONS website.

In Scotland, the percentage of people testing positive for COVID-19 increased in nursery and primary age children and for those around 40 in recent weeks. The trends are uncertain for all other ages.

Caution should be taken in over-interpreting small movements in the latest trend.

More information on the percentage of people testing positive by age breakdown in Scotland can be found in the accompanying dataset for Scotland.

Estimates for non-overlapping 14-day periods (which underpin our modelled estimates) by age group are available in ONS Coronavirus (COVID-19) Infection Survey datasets and are provided as an alternative measure over time for context.

Modelled estimate of the proportion of the private residential population testing positive for COVID-19 in each of the four nations of the UK  

In Scotland and England, the percentage of people testing positive for COVID-19 has increased in the most recent week. In Wales and Northern Ireland, the trend in the percentage of people testing positive in private residential households is uncertain in the most recent week. For all Four Nations, the most recent week of estimates is for 10 to 16 December.

Figure 3: Modelled daily estimates of the percentage of the private residential population testing positive for COVID-19 in each of the four nations of the UK, between 5 November and 16 December 2021, including 95% credible intervals (see notes 2,3,4,5,6)

Table 1: Modelled estimates of the proportion of the private residential population testing positive for COVID-19, and corresponding 95% credible intervals, in the week 10 to 16 December 2021 (see notes 1,3,4,5)

Nation	Estimated percentage of the population that had COVID-19	Estimated number of people who had COVID-19	Estimated ratio of people who had COVID-19
England	2.21% (2.10% to 2.32%)	1,202,300 (1,146,800 to 1,263,000)	1 in 45 (1 in 50 to 1 in 45)
Northern Ireland	2.06% (1.59% to 2.60%)	37,800 (29,100 to 47,700)	1 in 50 (1 in 65 to 1 in 40)
Scotland	1.45% (1.20% to 1.72%)	76,200 (63,100 to 90,500)	1 in 70 (1 in 85 to 1 in 60)
Wales	1.79% (1.46% to 2.15%)	54,400 (44,300 to 65,500)	1 in 55 (1 in 70 to 1 in 45)

Estimated percentages of those testing positive for COVID-19 by variant

The Omicron variant (B.1.1.529) of COVID-19 has changes in one of the three genes that coronavirus swab tests detect, known as the S-gene. This means in cases compatible with the Omicron variant, the S-gene is no longer detected by the current test. When there is a high viral load (for example, when a person is most infectious) absence of the S-gene in combination with the presence of the other two genes (ORF1ab and N-genes) is a reliable indicator of the Omicron variant (B.1.1.529). 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 Omicron variant.

In Scotland, the estimated percentage of the population living in private residential households testing positive for cases compatible with the Omicron variant of COVID-19 has increased in the most recent week (10 to 16 December 2021). In the most recent two weeks, the percentage of people testing positive for Delta variant compatible cases (B.1.617.2 and its genetic descendants) has decreased, but the trend is uncertain in the most recent week.

For the other nations, the percentage of cases compatible with the Omicron variant has increased in England, Wales and Northern Ireland in the most recent week (10 to 16 December 2021). In the same week, the percentage cases compatible with the Delta variant (B.1.617.2 and its genetic descendants) has decreased in England, Wales and Northern Ireland.

There is considerable uncertainty surrounding these estimates by variant due to the small numbers of positives detected in Scotland. This data should be treated with caution. There are further uncertainties given that not all cases that are positive on the ORF1ab and N-genes will be the Omicron variant.

Between late-July and early-November 2021, infections compatible with the Delta variant were the most common in all four UK countries. During this period, over 99% of all COVID-19 infections detected in the study where a genetic sequence was obtained were the Delta variant or a genetic descendant/sub-lineage of the Delta variant. This was described by ONS in their main variant analysis on the 23 July 2021.

The World Health Organisation (WHO) have suggested new names for Variants of Concern and Variants of Interest to assist with public discussions of the variants, which can be found as a table on the WHO website.

Whole Genome Sequencing analysis was produced by research partners at the University of Oxford, for more details please see the report on the ONS website.

Further information

The latest estimate of the proportion of those living in private residential households aged 16 and over in Scotland who would have tested positive for COVID-19 antibodies was published on 23 December 2021 on the Scottish Government website and ONS website.

Recent analysis on the predictors of Omicron (B.1.1.529) positivity published on 21 December suggests that positive cases among school age children are much less likely to be compatible with Omicron (B.1.1.529) than positive cases among adults. Therefore, positivity in school age children is still primarily driven by infections with Delta (B.1.617.2 and its genetic descendants). More information on ONS analysis of predictors of Omicron (B.1.1.529) positivity is available in this statement.

An article on the characteristics of people who are more likely to test positive for coronavirus, and how often individuals are reporting social contact with other people outside their own household (either socially distanced or physical contact), was published on 16 December 2021 on the Scottish Government website and the ONS website.

An article on the prevalence of ongoing symptoms following coronavirus (COVID-19) infection in the UK was published on the ONS website on 2 December 2021. The article includes estimates of the prevalence of self-reported "long COVID", and the duration of ongoing symptoms following confirmed coronavirus infection, using UK Coronavirus (COVID-19) Infection Survey data to 31 October 2021.

A technical article on updated estimates of the prevalence of post-acute symptoms among people with coronavirus (COVID-19) – commonly known as “long COVID” – in the UK was published on the ONS website on 16 September 2021. This article contains experimental estimates from three approaches to estimating the percentage of people testing positive for coronavirus (COVID-19) and who experience symptoms four or more weeks after infection, broken down by demographic and viral characteristics, using UK Coronavirus Infection Survey data. Please note that the estimates in this article are presented as percentages of those testing positive for COVID-19, and are not comparable to the estimates published on 4 November which are presented as percentages of the private residential population.

A technical article on predictors of positivity across countries of the UK for coronavirus was published on the ONS website on 28 October 2021. The article presents the methods and results of analysis to identify characteristics of people who are more likely to test positive for coronavirus (COVID-19) in Wales, Northern Ireland, and Scotland. It screens the different characteristics of people sampled in the Coronavirus (COVID-19) Infection Survey (CIS) who have and have not tested positive for COVID-19 and uses a statistical model to assign risk to each of these characteristics.

A technical article on positivity after vaccination (UK) was published on 17 June on the ONS website.

How this data can be used

The data can be used for:

• estimating the number of current positive cases in the private residential population, including cases where people do not report having any symptoms
• estimating the number of new cases and change over time in positive cases

The data cannot be used for:

• measuring the number of cases and infections in care homes, hospitals and other communal establishments
• 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

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 communal establishments. The population used in this analysis relates to the private residential population aged two years and over.

In the latest six-week period, there were 55,161 swab tests from 34,160 people, with a total of 600 positive tests in 562 people from 435 households. In the latest two-week period, there were 15,340 swab tests from 14,726 people, with a total of 170 positive tests in 167 people from 130 households.

The COVID-19 Infection Survey bulletins and datasets 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. The ratios presented are rounded to the nearest 100 if over 1,000, to the nearest 10 if under 1,000 and to the nearest 5 if under 100. These ratios do not represent a person's risk of becoming infected, since risk of infection depends on a number of factors such as contact with others or whether a person has been vaccinated.

2. There is more uncertainty around estimates for the latest three reported days (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.

3. Modelled estimates are not directly comparable with the 14-day weighted estimates provided in the accompanying dataset on the ONS website. The 14-day weighted estimates underpin the modelled estimates and are provided for context. 14-day weighted estimates are not directly comparable with the weekly modelled estimates due to the differing methodology, however they have been included in Figure 2 as they were reported as the official estimates for Scotland before the weekly modelled estimates became available.

4.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. A credible interval gives an indication of the degree of uncertainty of an estimate, showing the precision of a sample estimate.

5. 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.

6. 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.

7. As there was no publication on 15 January 2021 there are no official estimates available for the week ending 9 January 2021. However, ONS conducted some additional analysis to assess what the estimate may have been, therefore this estimate is included in Figure 2, shown in light grey.

8. 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.

9. The table below contains the composition of each CIS region in Scotland, by Health Board and Local Authority area. Local Authority areas map to the Health Board areas.

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

10. Sub-regional estimates are based on a different model to our headline estimates. Our sub-regional estimates are calculated as an average over a thirteen-day period and should not be compared to our headline positivity estimates which are for a single reference date. Therefore, the sub-regional figures may differ from the headline estimates because they are averaged over a longer time period. If a trend is changing, the figures shown in Figure 5 may not reflect the change we are seeing in our headline estimates.

11. To provide more precision to sub-regional estimates, ONS updated its method on 26 November 2021 to model the last 13 weeks of data instead of the last 7 weeks of data, as in previous releases.

12. There is more uncertainty around incidence estimates for the latest seven reported days (as shown by the vertical dashed line), as modelled estimates can change as additional data is included.

13. Please note, due to different trends across the four countries, Wales, Scotland and Northern Ireland have been modelled separately to England. In previous weeks, Northern Ireland has been modelled separately, and England, Wales and Scotland have been modelled together. England’s sub-regional estimates have been modelled with Wales and Scotland included.

14. Please note, no incidence rate estimates were provided in the release on 3 September 2021, for data relating to the week 7 to 13 August 2021, due to the August bank holiday in England and Wales.

15. Please note that a new category was added on the scale of this map in the 24 September 2021 publication – the “1.50% to <2.00%” category has been split into the “1.50% to <1.75%” and “2.75% to <2.00%” categories.

16. Estimates are based on confirmed positive test results. The remaining swabs are either negative, inconclusive or test failures. ONS are working with the laboratories to understand consistency in the identification of inconclusive results, that could be weak positive results. The impact of this on our estimates of positive infections is likely to be very small and unlikely to affect the trend.

17. Due to the timeliness of the data received from the laboratories and occurrence of public holidays there are gaps and overlaps between some of our official estimates, this does not impact the comparability of these estimates.

18. Omicron variant compatible positives are defined as those that are positive on the ORF1ab-gene and N-gene, but not the S-gene. Delta variant compatible positives are defined as those that are positive on the ORF1ab, N-gene and S-gene. Positives where the virus is too low for the variant to be identifiable are defined as those that are positive with all other gene patterns. These definitions are regardless of cycle threshold (Ct) value.

19. Data should be treated with caution.  Most cases with pattern S+ORF1ab+N will be the Delta variant, but some cases with pattern ORF1ab+N will also be the Delta variant where the S gene was not detected for other reasons, such as low viral load.

20. Cases where the virus is too low for the variant to be identifiable are likely to be people very recently infected or those who are recovering from their infection; people who get new infections after vaccination may also be in this group.