Coronavirus (COVID-19): ONS Infection Survey – headline results – 4 February 2022

ONS Coronavirus (COVID-19) Infection Survey Results 4 February 2022

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.

Main Points

To ensure that the latest estimates on positivity are available at the earliest opportunity during this period of high infections, the ONS and the Scottish Government published headline results on Wednesday. The analysis in this article provides further breakdowns for the same period and a longer time series.

In the week 23 to 29 January 2022, the estimated percentage of the population living in private residential households testing positive for COVID-19 in Scotland was 3.52% (95% credible interval: 3.08% to 4.00%). The percentage of people testing positive in Scotland has decreased over the most recent two weeks, however the trend is uncertain in the most recent week.

This equates to an estimated 185,100 people living in private residential households in Scotland that had COVID-19 at any given time (95% credible interval: 162,100 to 210,800), or around 1 in 30 people (95% credible interval: 1 in 30 to 1 in 25). Reported headline positivity estimates contain Omicron and all other variants.

In the week 23 to 29 January 2022, estimates for the other nations of the UK are as follows:

• in England, the percentage of people testing positive in private residential households remained high, with substantial variation in trends across different regions. The estimated percentage of people testing positive is 4.83% (95% credible interval: 4.67% to 5.00%), equating to around 1 in 20 people (95% credible interval: 1 in 20 to 1 in 20).
• in Wales, the percentage of people testing positive in private residential households increased in the most recent week: 4.57% (95% credible interval: 3.94% to 5.24%), equating to around 1 in 20 people (95% credible interval: 1 in 25 to 1 in 20).
• in Northern Ireland, the trend in the percentage of people testing positive in private residential households increased in the most recent week: 7.43% (95% credible interval: 6.44% to 8.46%), equating to around 1 in 15 people (95% credible interval: 1 in 15 to 1 in 10).

In Scotland, estimates for the percentage of people testing positive for COVID-19 in private residential households increased for primary school aged children and decreased for young adults. The trends were uncertain for secondary school ages, as well as the older ages.

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

This reference week for positivity estimates for all four UK nations is 23 to 29 January 2022.

It is estimated that in the most recent week (23 to 29 January 2022), the percentage of those living in private residential households in Scotland that had COVID-19 was 3.52%. A 95% credible interval for this figure is 3.08% to 4.00% (see note 4 for further information about credible intervals).

In the same week (23 to 29 January 2022), the ONS estimate that 185,100 people living in private residential households in Scotland at any given time had COVID-19. A 95% credible interval for this figure is 162,100 to 210,800. This equates to around 1 in 30 people (95% credible interval: 1 in 30 to 1 in 25).

As shown in Figure 1, the percentage of people testing positive for COVID-19 in Scotland has decreased over the most recent two weeks, however the trend is uncertain 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.

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

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 19 December 2021 and 29 January 2022, 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 29 January 2022. 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 2021. Estimates then fluctuated for a few weeks, before consistently increasing from late-November to a peak in the week 1 to 7 January 2022. The percentage of people testing positive for COVID-19 then decreased up to the week ending 22 January 2022. In the most recent week, the trend is uncertain. 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 29 January 2022, 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, estimates for the percentage of people testing positive for COVID-19 in private residential households increased for primary school aged children and decreased for young adults. The trends were uncertain for secondary school ages, as well as the older ages.

Figure 3: Modelled daily estimates of the percentage of the private residential population in Scotland testing positive for COVID-19, by reference age, between 19 December 2021 and 29 January 2022, including 95% confidence intervals (see notes 2,5,6,8)

ONS publish an interactive chart in their weekly bulletin.

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.

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

Figure 4 shows 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. In England, the percentage of people testing positive remained high in the most recent week (23 to 29 January 2022). In Wales and Northern Ireland, the percentage of people testing positive increased in the most recent week. In Scotland, the percentage of people testing positive for COVID-19 decreased in the two weeks up to 29 January 2022, but the trend was uncertain in the most recent week.

Figure 4: 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 19 December 2021 and 29 January 2022, including 95% credible intervals (see notes 2,3,4,5,6)

Modelled estimates of the proportion of the private residential population testing positive for COVID-19 for the most recent week can be found in Table 1.

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 23 to 29 January 2022 for the four nations of the UK (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	4.83% (4.67% to 5.00%)	2,633,100 (2,544,100 to 2,725,100)	1 in 20 (1 in 20 to 1 in 20)
Northern Ireland	7.43% (6.44% to 8.46%)	136,300 (118,200 to 155,200)	1 in 15 (1 in 15 to 1 in 10)
Scotland	3.52% (3.08% to 4.00%)	185,100 (162,100 to 210,800)	1 in 30 (1 in 30 to 1 in 25)
Wales	4.57% (3.94% to 5.24%)	139,000 (119,800 to 159,300)	1 in 20 (1 in 25 to 1 in 20)

Modelled estimates of the percentage of the private residential 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 9.

The sub-region with the highest modelled estimate for the percentage of people testing positive was CIS Region 127 (NHS Lanarkshire) at 4.76% (95% credible interval: 3.91% to 5.81%).

The sub-region with the lowest modelled estimate was Region 123 (NHS Grampian, NHS Highland, NHS Orkney, NHS Shetland and NHS Western Isles), at 2.74% (95% credible interval: 2.24% to 3.38%).

This data is shown in Figure 5, and is also available as a dynamic map (see notes 3,4,5,9,10,12,14).

Sub-regional estimates are based on a different model to the headline estimates, and should not be compared to headline positivity estimates. The sub-regional figures may differ from the headline estimates because they are averaged over a longer time period.

The number of people sampled in each sub-regional area who tested positive for COVID-19 is lower relative to the respective overall national samples. This means there is a higher degree of uncertainty in these estimates; caution should be taken, and the uncertainty of the estimates and wide credible intervals taken into account, when interpreting or ranking them.

Figure 5: Modelled estimates of the percentage of the private residential population within each CIS sub-region who would have tested positive for COVID-19 in the week 23 to 29 January 2022 in the four nations of the UK (see notes 3,5,9,10,12,14)

 

Number of new COVID-19 infections in Scotland

ONS provides estimates of incidence, a measure of new Polymerase Chain Reaction (PCR)-positive cases in a given time period. This gives the rate at which new positives occur, and subsequently become detectable, within the population.

The reference date used for the official estimates of incidence is 14 days prior to the positivity reference date (26 January 2022), with credible intervals provided until 7 days after the incidence reference date. Therefore, there is a time lag of 2 weeks between the incidence estimate and the positivity estimate. The incidence reference date used in this publication is 12 January 2022, relating to the week from 9 to 15 January 2022.

For more information on how estimates of incidence are calculated, please see COVID-19 Infection Survey: methods and further information.

In Scotland, during the week 9 to 15 January 2022, it is estimated that there were 25.78 new PCR-positive COVID-19 cases per 10,000 people per day (95% credible interval: 18.09 to 33.37). This equates to 13,600 new positive cases in Scotland per day (95% credible interval: 9,500 to 17,600). The estimated incidence of new PCR positive COVID-19 cases continued to decrease in the most recent week.

Modelled daily estimates of incidence rates, and accompanying credible intervals, are represented in Figure 6 by the blue line and grey shading. The model smooths the series to understand the trend and will be revised to incorporate new test results. Modelled daily estimates are used to calculate the official reported/indicative estimate.

Official reported/indicative estimates of incidence rates, are based on the modelled estimate for the midpoint of the week. Indicative estimates are denoted by pale blue circles, while the official estimates are denoted by dark blue circles, in Figure 6 and 7. Indicative estimates are presented on the official estimates charts, but were not previously published.

Figure 6: Modelled daily estimates and official reported/indicative estimates of incidence rates in Scotland between 9 December 2021 and 19 January 2022, including 95% credible intervals (see notes 4,5,6,11,13)

  

Figure 7: Official reported/indicative estimates of incidence rates in Scotland between 25 October 2020 and 15 January 2022, including 95% credible intervals (see notes 4,5,6,13)

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

The Omicron variant currently dominant in the UK is BA.1. This variant has changes in one of the three genes that the coronavirus swab used in the survey tests detects, known as the S-gene, which means 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 this Omicron variant (BA.1). 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 this Omicron variant. The sub-variant Omicron BA1.1 also mostly has gene pattern ORF1ab + N. Therefore, gene pattern matching used in our main variant analysis cannot distinguish between Omicron BA.1 and Omicron BA1.1.

In contrast, the Omicron sub-variant BA.2 does not have changes in the S gene, and therefore the detection of all three genes, or the S-gene and either ORF1ab or N is usually a reliable indicator of this sub-variant of Omicron. Delta also does not have changes in the S-gene, and therefore has identical gene patterns to Omicron BA.2. This means that gene pattern matching cannot distinguish between Omicron BA.2 cases and Delta cases. For this reason, we label cases with gene patterns ORF1ab + N + S, ORF1ab + S and N + S as ‘not compatible with Omicron BA.1’ in the main variant analysis. The genome sequencing analysis suggests that a clear majority of cases with these gene patterns are now Omicron BA.2, with relatively few being Delta. For this reason, 'not compatible with Omicron BA.1' estimates are now likely to mostly reflect trends in BA.2, although Delta may still be having a very small impact.

Since the end of December, infections compatible with the Omicron BA.1 variant have been the most common in all four UK countries. In the week ending 29 January 2022, the trend in the percentage of people testing positive not compatible with Omicron BA.1 was uncertain in Scotland. This group of positives will include Omicron BA.2 and Delta cases; the majority of recent cases will be Omicron BA.2 based on our genetic sequencing.

In the week ending 23 January 2022, 96.6% of all sequenced COVID-19 infections were the Omicron BA.1 variant or its sub-variants, and 2.8% were the Omicron BA.2 sub-variant. The latest complete sequenced data lags our main variant analysis and these percentages are an average over a whole week to 23 January 2022

Because of the high proportion of a single variant across Scotland, we have not included charts showing breakdown by variant in this article. However, variant analysis by country and by region can be found in the technical dataset on the ONS website. We will continue to monitor infections by variant and will reintroduce the charts when considered helpful.

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 is produced by Northumbria University and analysis is produced by research partners at the University of Oxford, for more details please see the report on the ONS website.

Further information

During this period of high infections, the ONS have decided to publish headline results from the COVID-19 Infection Survey two days early. This means that the latest estimates on infection levels are available at their earliest opportunity and further breakdowns for the same period and a longer time series will continue to be published on Fridays. These early estimates are provisional and are subject to change as we receive more data, but they have undergone sufficient quality assurance to ensure that they are based upon an acceptable number of test results received up to the end of the reference week.

These early headline releases on the latest estimates of the COVID-19 Infection Survey can be found on the ONS website and are accompanied by a limited dataset which includes estimates of positivity by country, regions in England, and age groups in England.

The latest estimate of the proportion of those living in private residential households in Scotland who would have tested positive for COVID-19 antibodies was published on 26 January 2022 on the Scottish Government website and ONS website. From 13 January 2022, based on academic research, these publications also present the percentage of adults with antibodies to SARS-CoV-2 at or above a higher antibody threshold, which provides greater protection against COVID-19 following vaccination. From 26 January 2022, these publications also present analysis on the estimated percentage of children aged 8 to 15 years who would have tested positive for antibodies to SARS-CoV-2 since 29 November 2021.

An article on how often individuals in Scotland are reporting social contact with other people outside their own household (either socially distanced or physical contact), and estimates of the percentage of people testing positive that reported symptoms, was published on 19 January 2022 on the Scottish Government website and the ONS website. An article on characteristics of people testing positive for COVID-19 at the UK level was published on the ONS website on 2 February 2022.

A technical article on self-reported “long COVID” after two doses of a COVID-19 vaccine in the UK was published on the ONS website on 26 January 2022. The article explores the likelihood of participants in the UK reporting “long COVID” symptoms at least 12 weeks after COVID-19 infection, comparing CIS participants who had received two doses of a vaccine prior to infection with participants who were unvaccinated, using UK data to 30 November 2021.

An article on the prevalence of ongoing symptoms following COVID-19 infection in the UK was published on the ONS website on 3 February 2022. The article includes estimates of the prevalence of self-reported “long COVID”, and the duration of ongoing symptoms following confirmed COVID-19 infection, using UK data to 2 January 2022.

A technical article on updated estimates of the prevalence of post-acute symptoms among people with 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 COVID-19 and who experience symptoms four or more weeks after infection, broken down by demographic and viral characteristics, using UK CIS 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 which are presented as percentages of the private residential population.

A technical article on predictors of positivity across countries of the UK for COVID-19 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 COVID-19 in Wales, Northern Ireland, and Scotland. It screens the different characteristics of people sampled in the 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 positive cases among the population living in private households, including cases where people do not report having any symptoms
• identifying differences in numbers of positive cases between UK countries and different regions in England
• 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/or other communal establishments
• 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 Scotland, in the latest six-week period, there were 52,056 swab tests from 33,756 people, with a total of 1,531 positive tests in 1,487 people from 1,165 households. In the latest two-week period, there were 15,540 swab tests from 15,414 people, with a total of 448 positive tests in 448 people from 353 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 quickly, 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 will mostly have a gene pattern ORF1ab+N+S (or occasionally S+ORF1ab and S+N), and so in this analysis are defined as those that are positive on the ORF1ab, N-gene and S-gene, or positive on the S-gene and either ORF1ab or the N-gene.

19. Data should be treated with caution. Not all cases positive on the S-gene will be the Delta variant, and 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.

21. Please note that the categories on this map were altered in the 7 January 2022 publication – there are now seven categories in intervals of 1%.