Publication - Statistics

Coronavirus (COVID-19): ONS Infection Survey - headline results - 19 March 2021

Published: 19 Mar 2021

Results from the ONS COVID-19 infection survey from 19 March 2021.

Published:
19 Mar 2021
Coronavirus (COVID-19): ONS Infection Survey - headline results - 19 March 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

More detailed analysis will be available in future releases.

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.

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

It is estimated that in the most recent week (7 to 13 March 2021), the percentage of the population in Scotland that had the coronavirus (COVID-19) was 0.37%. A 95% credible interval for this figure is 0.27% to 0.49%.

In the same week, it is estimated that at any given time 19,300 people in Scotland had COVID-19. A 95% credible interval for this figure is 14,100 to 25,600. This equates to around 1 in 275 people (95% credible interval: 1 in 375 to 1 in 205).

There appears to be some increase in the percentage of people testing positive for COVID-19 in Scotland in the week ending 13 March, as shown in Figure 1.

The increase in the proportion of people estimated to have COVID-19 in Scotland is likely driven by those aged under around 50. The proportion of people aged over 70 testing positive for COVID-19 may still be decreasing in the latest week.

Figure 1: Modelled estimates of the percentage of the population in Scotland testing positive for COVID-19 between 31 January and 13 March 2021, including 95% credible intervals (see notes 2,3,4,5,6)

Modelled daily estimates of the percentage of the population testing positive for COVID-19 in Scotland by single year of age, between 31 January and 13 March, are available in an interactive visualisation and accompanying dataset on the ONS website. 

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

The trend of the percentage of people testing positive for COVID-19 varied across the four nations of the UK in the week ending 13 March 2021.

There appears to be some increase in the percentage of people testing positive for COVID-19 in Scotland.  The percentage of people testing positive for COVID-19 has continued to decrease in England and Wales, but the rate of decrease appears to have slowed in Wales in the most recent week. The percentage of people testing positive for COVID-19 in Northern Ireland appears level, although there is high uncertainty.

Figure 2: Modelled estimates of the percentage of the population testing positive for COVID-19 in each of the four nations of the UK, between 31 January and 13 March 2021 including 95% credible intervals (See notes 2,3,4,5)

*Northern Ireland

Table 1: Modelled estimates of the proportion of the population testing positive for COVID-19, and corresponding 95% credible intervals, between 7 and 13 March 2021 for the four nations of the UK (See notes 1,2,3,4)

Nation

Estimated percentage of population that had COVID-19

Estimated number of people who had COVID-19

Estimated ratio of people who had  COVID-19

England

0.29% (0.26% to 0.33%)

160,200 (142,000 to 179,400)

1 in 340 (1 in 385 to 1 in 305

Northern Ireland

0.32% (0.18% to 0.51%)

5,800 (3,300 to 9,400)

1 in 315 (1 in 560 to 1 in 195)

Scotland

0.37% (0.27% to 0.49%)

19,300 (14,100 to 25,600)

1 in 275 (1 in 375 to 1 in 205

Wales

0.23% (0.14% to 0.35%)

7,000 (4,300 to 10,600)

1 in 430 (1 in 715 to 1 in 290)

Modelled estimates of the percentage of the 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 7.

This data is shown in Figure 3, and is also available as a dynamic map. (See notes 1,2,3,4,5,7).

Sub-regional estimates are based on a different model to the headline estimates. Sub-regional estimates are calculated as an average over a seven-day period and should not be compared to the headline positivity estimates which are for a single reference date. As a result, sub-regional estimates are not as responsive as the headline positivity estimates to changes in the most recent days.

In the data used to produce these estimates, the number of people sampled in each sub-regional area who tested positive for COVID-19 was 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.

As the percentage of people testing positive decreases, sub-regional estimates are subject to increased uncertainty as captured in the credible intervals. This will continue to be monitored over the coming weeks.

The modelled estimates of the percentage of the population testing positive for COVID-19 in each sub-region of Scotland vary between 0.13% and 0.30%.

The sub-region in Scotland with the highest modelled estimate of the percentage of people testing positive for COVID-19 was CIS Region 127 (NHS Lanarkshire), at 0.30% (95% credible interval: 0.22% to 0.40%).

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 0.13% (95% credible interval: 0.09% to 0.17%).

In the latest week, the percentage of the population testing positive for COVID-19 was under 0.25% in five of the six CIS regions in Scotland (123, 124, 125, 126 and 128). The percentage of the population testing positive for COVID-19 in the other CIS region in Scotland (127) was between 0.25% and 0.50%. (See note 7).

Figure 3: Modelled estimates of the percentage of the population within each CIS sub-region who would have tested positive for COVID-19 in the week 7 to 13 March 2021 in the UK (See notes 3,7)

Estimate of the percentage of those testing positive for COVID-19 whose test results were compatible with the new UK variant

A new variant of COVID-19 was identified in the UK in mid-November 2020. The new UK variant of COVID-19 has changes in one of the three genes which coronavirus swab tests detect, known as the S-gene. This means in cases compatible with the new variant, the S-gene is no longer detected by the current test. While there are other reasons why a positive swab test may not detect the S-gene, absence of the S-gene has become a reliable indicator of the new UK variant in COVID-19. 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 new UK variant.

In contrast the Brazilian and South African variants have an S-gene that is detectable with the current test and will therefore be included in the “not compatible with new variant” group of COVID-19, where the virus level is high enough to identify this. Which of these types of COVID-19 are compatible with these variants cannot be identified from the swab PCR test alone. You can read more about the new UK variant in the blog published by ONS.

There are early signs of an increase in the percentage testing positive compatible with the UK variant in Scotland in the week ending 13 March. The percentage testing positive compatible with the UK variant decreased in England in the week ending 13 March 2021. In Wales and Northern Ireland, the trend in the percentage testing positive compatible with the UK variant is uncertain.

Detailed analysis on the new UK variant is no longer included in the Scottish Government COVID-19 Infection Survey publication. This data will continue to be published in the accompanying reference tables on the ONS website. Trends in different variants will continue to be monitored over the coming weeks and the charts will be reintroduced into the publication if there is a variant that can be identified using survey tests that appears to be affecting the trends in the percentage of people testing positive for COVID-19.

Quality and methodology information

Fieldwork in Scotland has been scaled up to test 15,000 unique participants per fortnightly period. More detailed analysis, such as examining the characteristics of those testing positive for COVID-19 and establishing the average number of new infections per week will be produced when the sample size permits.

The latest estimate of the proportion of people in Scotland who would have tested positive for COVID-19 antibodies was published on 16 March on the Scottish Government website and ONS website.

How this data can be used

The data can be used for:

  • estimating the number of current positive cases in the community, including cases where people do not report having any symptoms

The data cannot be used for:

  • measuring the number of cases and infections in care homes, hospitals and other institutional settings
  • estimating the number of positive cases and new infections in smaller geographies, such as towns and cities
  • providing information about recovery time of those infected
  • producing a UK estimate; ONS now have estimates for England, Scotland, Wales and Northern Ireland, but these cannot be added up or averaged to understand the UK infection rate

Methodology

The results are based on nose and throat swabs provided by participants to the study, obtained from fieldwork which started in Scotland on 21 September 2020.

The results are for private households only, and do not apply to those in hospitals, care homes or other institutional settings. The population used in this analysis relates to the community population aged two years and over.

In the latest six-week period, there were 77,209 swab tests from 30,743 people, with a total of 358 positive tests in 292 people from 241 households. In the latest two-week period, there were 18,660 swab tests from 16,636 people, with a total of 62 positive tests in 61 people from 52 households.

The Infection Survey bulletins available on the ONS website also include results for England, Wales and Northern Ireland.

The Welsh Government and the Department of Health in Northern Ireland also publish results from the COVID-19 Infection Survey for Wales and Northern Ireland respectively:

Further details on the methodology used can be found on the ONS website.

Notes

  1. Any ratios presented are rounded to the nearest 5.
  2. There is more uncertainty around estimates after 10 March (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.
  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.
  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. 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