Coronavirus (COVID-19): ONS Infection Survey – headline results – 18 March 2022

ONS Coronavirus (COVID-19) Infection Survey Results 18 March 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

In the week 6 to 12 March 2022, the estimated percentage of the population living in private residential households testing positive for COVID-19 in Scotland was 7.15% (95% credible interval: 6.56% to 7.79%). The estimated percentage of people testing positive in Scotland continued to increase in the most recent week.

In the same week, it is estimated that 376,300 people living in private residential households in Scotland had COVID-19 at any given time (95% credible interval: 345,400 to 409,900); this equates to around 1 in 14 people (95% credible interval: 1 in 15 to 1 in 13). The reported headline positivity estimates contain Omicron BA.1 and BA.2 variants and all other variants.

In the week 6 to 12 March 2022, estimates for the other nations of the UK are as follows:

• in England, the percentage of people testing positive continued to increase in the most recent week. The estimated percentage of people testing positive is 4.87% (95% credible interval: 4.72% to 5.02%), 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 continued to increase in the most recent week. The estimated percentage of people testing positive is 4.13% (95% credible interval: 3.56% to 4.77%), equating to around 1 in 25 people (95% credible interval: 1 in 30 to 1 in 20).
• in Northern Ireland, the percentage of people testing positive increased in the most recent two weeks, however the trend was uncertain in the most recent week. The estimated percentage of people testing positive is 7.12% (95% credible interval: 6.17% to 8.13%), equating to around 1 in 14 people (95% credible interval: 1 in 16 to 1 in 12).

In Scotland, in the most recent week, the percentage of people testing positive increased for all age groups except those of nursery and primary school age, for whom the trend was uncertain.

In Scotland, the percentage of infections compatible with the Omicron BA.2 variant has increased in the most recent week. The percentage of infections compatible with the Omicron BA.1 has decreased in the most recent week.  

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

This week, the reference week is 6 to 12 March 2022 for all four nations.

It is estimated that in the most recent week (6 to 12 March 2022), the percentage of those living in private residential households in Scotland that had COVID-19 was 7.15%. A 95% credible interval for this figure is 6.56% to 7.79% (see note 4 for further information about credible intervals). In the latest two weeks, the estimates of positivity have surpassed the previous peak from early January 2022 to be the highest estimates since the survey began reporting for Scotland in October 2020.

In the same week, the ONS estimate that 376,300 people living in private residential households in Scotland at any given time had COVID-19. A 95% credible interval for this figure is 345,400 to 409,900. This equates to around 1 in 14 people (95% credible interval: 1 in 15 to 1 in 13).

As shown in Figure 1, the percentage of people testing positive for COVID-19 in Scotland has continued to increase 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 30 January 2022 and 12 March 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 12 March 2022.

The estimated percentage of the private residential population testing positive for COVID-19 has been increasing for the past seven weeks. In the latest two weeks, the estimates of positivity have surpassed the previous peak from early January 2022 to be the highest estimates since the survey began reporting for Scotland in October 2020. 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 12 March 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, in the most recent week, the percentage of people testing positive increased for all age groups except those of nursery and primary school age, for whom the trend was uncertain.

Figure 3: Modelled daily estimates of the percentage of the private residential population in Scotland testing positive for COVID-19, by reference age, between 30 January 2022 and 12 March 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 5 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, Wales and Scotland, the estimated percentage of people testing positive continued to increase in the week to 12 March 2022. In Northern Ireland, the estimated percentage of people testing positive increased in the most recent two weeks, however 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 the four UK nations, between 30 January and 12 March 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 daily estimates of the percentage of the private residential population testing positive for COVID-19 in the four UK nations, between 6 and 12 March 2022, including 95% credible intervals (see notes 2,3,4,5,6)

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	4.87% (4.72% to 5.02%)	2,653,200 (2,571,500 to 2,739,700)	1 in 20 (1 in 20 to 1 in 20)
Northern Ireland	7.12% (6.17% to 8.13%)	130,600 (113,100 to 149,100)	1 in 14 (1 in 16 to 1 in 12)
Scotland	7.15% (6.56% to 7.79%)	376,300 (345,400 to 409,900)	1 in 14 (1 in 15 to 1 in 13)
Wales	4.13% (3.56% to 4.77%)	125,400 (108,100 to 144,900)	1 in 25 (1 in 30 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 7.94% (95% credible interval: 6.57% to 9.58%).

The sub-regions with the lowest modelled estimate were CIS Region 123 (NHS Grampian, NHS Highland, NHS Orkney, NHS Shetland and NHS Western Isles), at 6.09% (95% credible interval: 5.01% to 7.40%) and CIS Region 126 (NHS Lothian), at 6.09% (95% credible interval: 5.12% to 7.27%).

This data is shown in Figure 6, 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 6 to 12 March 2022 (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 (9 March 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 23 February 2022, relating to the week from 20 to 26 February 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 20 to 26 February 2022, it is estimated that there were 65.75 new PCR-positive COVID-19 cases per 10,000 people per day (95% credible interval: 56.60 to 75.63). This equates to 34,600 new positive cases in Scotland per day (95% credible interval: 29,800 to 39,800). The estimated incidence of new PCR positive COVID-19 cases per day has increased in the week to 26 February 2022.

Modelled daily estimates of incidence rates, and accompanying credible intervals, are represented in Figure 7 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 7 and 8. 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 20 January and 2 March 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 26 February 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 BA.1 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.

The Omicron variant BA.2 does not have changes in the S-gene, and therefore all three genes, or the S-gene and either ORF1ab or N, will usually be detected in infections with this variant. Delta also does not have changes in the S-gene, and therefore the same sets of genes will usually be detected with Delta and Omicron BA.2. However, our genome sequencing analysis shows that a clear majority of cases where we detect the S-gene are now Omicron BA.2, with relatively few being Delta. For this reason, we now label cases with gene patterns ORF1ab + N + S, ORF1ab + S and N + S as “compatible with the Omicron BA.2 variant” in our main variant analysis as estimates are now likely to mostly reflect trends in BA.2, although Delta may still be having a very small impact.

The Omicron BA.2 variant is now the most common variant in England, Wales, Northern Ireland and Scotland. In the week ending 13 March 2022, 76.1% of all sequenced COVID-19 infections from the survey were compatible with the Omicron BA.2 variant, and 23.9% were compatible with the Omicron BA.1 variant or its sub-variants. The latest complete sequenced data lags the main variant analysis and these percentages are an average over a whole week to 13 March 2022.

The main variant analysis is for a reference day, and therefore is not directly comparable with the sequencing data.

The following analysis looks at the percentage of the population with a positive test compatible with the Omicron BA.1 variant or with the Omicron BA.2 variant.

During periods of change in COVID-19 variants we will include a breakdown of estimated infections by variant to illustrate how the estimated percentage of people infected in the population is changing by variant (Figure 9). When nearly all infections are compatible with a dominant variant, we will no longer include this breakdown.

In Scotland, the percentage of infections compatible with the Omicron BA.2 variant has increased in the most recent week. The percentage of infections compatible with the Omicron BA.1 has decreased in the most recent week.

Figure 8: Modelled percentage of infections compatible with the Omicron BA.1 variant and Omicron BA.2 variant, based on nose and throat swabs, daily, in Scotland, 30 January 2022 to 12 March 2022 (see notes 5,6,18,19,20)

 

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

Early experimental data and analysis on economic activity and social change in the UK were published on the ONS website on 3 March 2022. This release includes modelled estimates of the proportion of the workforce self-isolating because of coronavirus by work sector, and the proportion of the working age population self-isolating because of coronavirus by country.

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 9 March 2022 on the Scottish Government website and ONS website.

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) was published on 2 March 2022 on the Scottish Government website. The ONS also published an article on 2 March 2022 on the contacts analysis, as well as UK level analysis on the characteristics of people testing positive for COVID-19 and estimates of the percentage of people testing positive that reported symptoms. This can be found on the ONS website.

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 March 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 (30 January to 12 March 2022), there were 53,423 swab tests from 33,498 people, with a total of 2,124 positive samples in 2,102 people from 1,624 households. In the latest two-week period (27 February to 12 March), there were 14,915 swab tests from 14,912 people, with a total of 792 positive samples in 792 people from 612 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, to the nearest 5 if under 100 and to 1 if under 20. This may result in credible intervals that appear to be similar to the estimated average ratio. 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 BA.1 variant-compatible positives are defined as those that are positive on the ORF1ab-gene and N-gene, but not the S-gene. This group includes Omicron BA.1.1.

19. Cases ‘not compatible with Omicron BA.1’ 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. These will include both Omicron BA.2 and Delta variants. The majority of recent infections not compatible with Omicron BA.1, are likely to be Omicron BA.2.

20. Data should be treated with caution. Not all cases positive on the S-gene will be the Omicron BA.2 or Delta variants, and some cases with pattern ORF1ab+N will also be the Omicron BA.2 or Delta variants where the S-gene was not detected for other reasons, such as low viral load.

21. 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.

22. 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%.