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

Published: 23 Jul 2021

Results from the ONS COVID-19 infection survey from 23 July 2021.

Published:
23 Jul 2021
Coronavirus (COVID-19): ONS Infection Survey – headline results – 23 July 2021

ONS Coronavirus (COVID-19) Infection Survey results 23 July 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.

Main points

In the week 11 to 17 July 2021, the estimated percentage of the community population (private households) testing positive for COVID-19 in Scotland was 1.24% (95% credible interval: 0.98% to 1.53%). The percentage of people testing positive for COVID-19 in the community population has increased in the most recent two weeks, however, the trend is uncertain in the most recent week.

This equates to an estimated 65,100 people in the community population in Scotland that had COVID-19 at any given time (95% credible interval: 51,600 to 80,500), or around 1 in 80 people (95% credible interval: 1 in 100 to 1 in 65).

In the week 11 to 17 July 2021, estimates for the other nations of the UK are as follows:

  • in England, the percentage of people testing positive in the community has continued to increase in the most recent week to 1.36% (95% credible interval: 1.26% to 1.46%).
  • in Wales, the trend in the percentage of people testing positive in the community has increased in the most recent week to 0.47% (95% credible interval: 0.31% to 0.67%).
  • in Northern Ireland, the percentage of people testing positive in the community has increased in the most week to 0.59% (95% credible interval: 0.31% to 0.98%).

The proportion of people testing positive is higher in the younger age groups. In the most recent week, the trend in the proportion of people testing positive in the community population in Scotland has increased for those of secondary school age and for adults aged under around 30. The trend is uncertain in those of nursery and primary school age, and in those aged over around 30.

The modelled estimates of the percentage of the community population testing positive for COVID-19 in each sub-region of Scotland vary between 0.75% and 2.23%.

The trend in the percentage of people in the community testing positive whose results are compatible with the Delta variant (B.1.617.2) increased over the most recent two weeks in Scotland, but was uncertain in the most recent week, 11 to 17 July 2021.

In Scotland, in week 27 June to 3 July 2021, it is estimated that there were 5,200 new positive cases per day (95% credible interval: 4,000 to 6,700). Please note, there is a lag of two weeks between the incidence estimate and the positivity estimate.

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

It is estimated that in the most recent week (11 to 17 July 2021), the percentage of the community population (private households) in Scotland that had the coronavirus (COVID-19) was 1.24%. A 95% credible interval for this figure is 0.98% to 1.53%.

In the same week, it is estimated that at any given time 65,100 people in the community in Scotland had COVID-19. A 95% credible interval for this figure is 51,600 to 80,500. This equates to around 1 in 80 people (95% credible interval: 1 in 100 to 1 in 65).

In Scotland, it is estimated that the percentage of people testing positive for COVID-19 in the community population has increased in 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.

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. 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 community population in Scotland testing positive for COVID-19 between 6 June and 17 July 2021, including 95% credible intervals (see notes 2,3,4,5,6)

Figure 1: Modelled daily estimates and official reported estimates of the percentage of the community population in Scotland testing positive for COVID-19 between 6 June and 17 July 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 the community population testing positive for COVID-19 between 3 October 2020 and 17 July 2021. As shown in Figure 2, there has been an increase in the estimated percentage of the community population testing positive for COVID-19 in the most recent weeks. 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 community population in Scotland testing positive for COVID-19 between 3 October 2020 and 17 July 2021, including 95% credible intervals (see notes 3,4,5,6,7)

Figure 2: Official reported estimates of the percentage of the community population in Scotland testing positive for COVID-19 between 3 October 2020 and 17 July 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

Figure 3 shows the percentage of people testing positive for COVID-19 by reference age, between 6 June and 17 July 2021. These estimates are based on modelled daily estimates of the percentage of the population testing positive for COVID-19 in Scotland by single year of age, which are available in an accompanying dataset on the ONS website.

The proportion of people testing positive is higher in the younger age groups. In the most recent week, the trend in the proportion of people testing positive in the community population in Scotland has increased for those of secondary school age and for adults aged under around 30. The trend is uncertain in those of nursery and primary school age, and in those aged over around 30.

Caution should be taken in over-interpreting small movements in the latest trend. As the percentage of people testing positive decreases, the positivity estimates by single year of age are subject to increased uncertainty as captured in the confidence intervals.

Figure 3: Modelled daily estimates of the percentage of the population in Scotland testing positive for COVID-19, by reference age, between 6 June and 17 July 2021, including 95% confidence intervals (see notes 2,5,6,8)

Figure 3: Modelled daily estimates of the percentage of the population in Scotland testing positive for COVID-19, by reference age, between 6 June and 17 July 2021, including 95% confidence intervals (see notes 2,5,6,8)ONS publish an interactive chart in their bulletin fortnightly.

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

In Scotland, the percentage of people testing positive in the community has increased in the most recent two weeks up to 17 July 2021, however the trend is uncertain in the most recent week. The percentage testing positive in the community has continued to increase in England and increased in Wales and Northern Ireland in the most recent week.

Figure 4: Modelled daily estimates of the percentage of the community population testing positive for COVID-19 in each of the four nations of the UK, between 6 June and 17 July 2021, including 95% credible intervals (see notes 2,3,4,5,6)

Figure 4: Modelled daily estimates of the percentage of the community population testing positive for COVID-19 in each of the four nations of the UK, between 6 June and 17 July 2021, including 95% credible intervals (see notes 2,3,4,5,6)

*Northern Ireland

Table 1: Modelled estimates of the proportion of the community population testing positive for COVID-19, and corresponding 95% credible intervals, in the week 11 to 17 July 2021 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

1.36% (1.26% to 1.46%)

741,700 (689,600 to 797,800)

1 in 75 (1 in 80 to 1 in 70)

Northern Ireland

0.59% (0.31% to 0.98%)

10,900 (5,700 to 17,900)

1 in 170 (1 in 320 to 1 in 100)

Scotland

1.24% (0.98% to 1.53%)

65,100 (51,600 to 80,500)

1 in 80 (1 in 100 to 1 in 65)

Wales

0.47% (0.31% to 0.67%)

14,400 (9,500 to 20,500)

1 in 210 (1 in 320 to 1 in 150)

Modelled estimates of the percentage of the community 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.

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

Sub-regional estimates are based on a different model to the headline estimates, and should not be compared to headline positivity estimates.

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.

The sub-region in Scotland with the highest modelled estimate of the percentage of people testing positive for COVID-19 was CIS Region 125 (NHS Greater Glasgow and Clyde), at 2.23% (95% credible interval: 1.79% to 2.78%).

The sub-region in Scotland with the lowest modelled estimate was Region 123 (NHS Grampian, NHS Highland, NHS Orkney, NHS Shetland and NHS Western Isles), at 0.75% (95% credible interval: 0.51% to 1.11%).

Please note that sub-regional estimates for Wales have not been included in this publication as further quality assurance is required.

Figure 5: Modelled estimates of the percentage of the community population within each CIS sub-region who would have tested positive for COVID-19 in the week 11 to 17 July 2021 in the UK (See notes 3,5,9)Figure 5: Modelled estimates of the percentage of the community population within each CIS sub-region who would have tested positive for COVID-19 in the week 11 to 17 July 2021 in the UK (See notes 3,5,9)

Number of new COVID-19 infections in Scotland

ONS have recently re-introduced 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.

Following review, ONS have changed the reference date used for the official estimates of incidence to 14 days prior to the positivity reference date (14 July 2021), 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 30 June 2021, relating to the week 27 June to 3 July.

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 27 June to 3 July 2021, it is estimated that there were 9.97 new PCR-positive COVID-19 cases per 10,000 people per day (95% credible interval: 7.55 to 12.72). This equates to 5,200 new positive cases in Scotland per day (95% credible interval: 4,000 to 6,700). The trend in incidence of new PCR positive COVID-19 cases is uncertain 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 27 May and 7 July 2021, including 95% credible intervals (see notes 4,5,6,10)

Figure 6: Modelled daily estimates and official reported/indicative estimates of incidence rates in Scotland between 27 May and 7 July 2021, including 95% credible intervals (see notes 4,5,6,10)

Figure 7: Official reported/indicative estimates of incidence rates in Scotland between 25 October 2020 and 3 July 2021, including 95% credible intervals (see notes 4,5,6)

Figure 7: Official reported/indicative estimates of incidence rates in Scotland between 25 October 2020 and 3 July 2021, including 95% credible intervals (see notes 4,5,6)

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

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.

The Alpha variant (B.1.1.7) of COVID-19 has changes in one of the three genes that COVID-19 swab tests detect, known as the S-gene. This means in cases compatible with the Alpha variant, the S-gene is not detected by the current test and has the pattern ORF1ab+N (S gene negative) in the main variant analysis.

Other variants of concern – including both the Delta variant (B.1.617.2) and the Beta variant (B.1.351) – are positive on all three genes, with the pattern ORF1ab+S+N. Based on recent information from genomic sequencing and national testing programmes, ONS state that it is likely that most ORF1ab+S+N cases in the UK will be the Delta variant. Therefore, if there is an increase in the prevalence the Delta strain, this will show up in the analysis as an increase in cases “Compatible with the Delta variant”. It is possible that some Delta variant infections do not test positive on the three genes, particularly if there is a low viral load. We expect these numbers to be small, but it is possible that some Delta cases may be categorised as Alpha compatible

This main variant analysis can therefore differentiate between these two groups of variants (ORF1ab+N positive or ORF1ab+S+N positive), but cannot differentiate between variants that have the same gene pattern for the three genes that COVID-19 swab tests detect. More information on individual variants and where they were first detected is available on the government variant dashboard.

Other variants, including the Eta variant (B.1.525), may also have the same pattern of gene positivity as the Alpha variant. At present these are rare in the UK so this group will continue to be described as compatible with the Alpha variant, but ONS will continue to keep this under review. You can read more about the UK variant in the blog published by ONS.

The percentage of people in the community testing positive whose results are compatible with the Delta variant (B.1.617.2) has increased in the two weeks up to 17 July 2021 in Scotland, but was uncertain in the most recent week. The percentage continued to increase in England and increased in Northern Ireland and Wales.

Figure 8: Estimated percentage of the population testing positive that are compatible with Delta variant, compatible with the Alpha variant, and other ‘not identifiable’ positive cases, in Scotland between 6 June and 17 July 2021 (See notes 2,4,5).

Figure 8: Estimated percentage of the population testing positive that are compatible with Delta variant, compatible with the Alpha variant, and other ‘not identifiable’ positive cases, in Scotland between 6 June and 17 July 2021 (See notes 2,4,5).*Alpha variant compatible positives are defined as those that are positive on the N-gene and ORF1ab-gene, but not the S-gene.

**Delta variant compatible positives 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.

Variant data is published in the accompanying reference tables on the ONS website.

Whole genome sequencing is undertaken on positive tests from the survey, where possible. In the UK in the most recent four weeks, up to the week ending 11 July 2021, the majority (98%) of sequences obtained were Delta (B.1.617.2) with Alpha (B.1.1.7) comprising most of the remainder (2%).

This analysis was produced by research partners at the University of Oxford.

Further information

The latest estimate of the proportion of community population aged 16 and over in Scotland who would have tested positive for COVID-19 antibodies was published on 21 July 2021 on the Scottish Government website and 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 1 July 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 6 June 2021.

An article on how often individuals are reporting social contact with other people outside their own household, either socially distanced or physical contact was published on 30 June 2021 on the Scottish Government website and ONS website.

An article on the symptom profile of strong positive cases in the UK was also published on 30 June 2021. The article includes estimates of the percentage of people testing positive that reported symptoms and the likelihood of reporting specific symptoms by nation. Analysis for Scotland was last published on the Scottish Government website on 5 May 2021. The article on the ONS website also includes analysis on the likelihood of testing positive for COVID-19 by patient-facing or non-patient facing job roles.

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 community, 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 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

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 55,375 swab tests from 31,568 people, with a total of 295 positive tests in 277 people from 230 households. In the latest two-week period, there were 15,689 swab tests from 14,702 people, with a total of 144 positive tests in 141 people from 111 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:

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.

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. 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.