Coronavirus (COVID-19): ONS Infection Survey - headline results - 26 March 2021

ONS Coronavirus (COVID-19) Infection Survey Results 26 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 (14 to 20 March 2021), the percentage of the population in Scotland that had the coronavirus (COVID-19) was 0.41%. A 95% credible interval for this figure is 0.30% to 0.54%.

In the same week, it is estimated that at any given time 21,500 people in Scotland had COVID-19. A 95% credible interval for this figure is 15,600 to 28,500. This equates to around 1 in 240 people (95% credible interval: 1 in 340 to 1 in 180).

In Scotland, the percentage of people testing positive for COVID-19 increased over the two weeks up to 20 March 2021, as shown in Figure 1.

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 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 circle).

Figure 1: Modelled daily estimates and official reported estimates of the percentage of the population in Scotland testing positive for COVID-19 between 7 February and 20 March 2021, including 95% credible intervals (see notes 2,3,4,5,6

The chart shows modelled daily estimates and official reported estimates of the percentage of the population in Scotland testing positive for COVID-19 between 7 February and 20 March 2021, including 95% credible estimates. The percentage of people testing positive for COVID-19 increased over the two weeks up to 20 March 2021.

Figure 2: Official reported estimates of the percentage of the population in Scotland testing positive for COVID-19 between 3 October 2020 and 20 March 2021, including 95% credible intervals (see notes 3,4,5,6)

The chart shows all official reported estimates of the percentage of the Scottish population testing positive for COVID-19, between 3 October 2020 to 20 March 2021, including 95% credible estimates. The percentage of people testing positive for COVID-19 increased over the two weeks up to 20 March 2021.

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 7 February and 20 March. 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 percentage of people testing positive for COVID-19 of nursery, primary school and secondary school age (reference ages 5, 10, 15) appears to have increased in the last two weeks up to 20 March 2021. The percentage testing positive for COVID-19 in young adults may be increasing but may be decreasing in older adults.

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

Figure 3: Modelled daily estimates of the percentage of the population in Scotland testing positive for COVID-19, by reference age, from 7 February to 20 March, including 95% credible intervals (see notes 2,4,5,6)

The charts shows modelled daily estimates of the percentage of the population in Scotland testing positive for COVID-19, by reference age, from 7 February to 20 March, including 95% credible intervals. There is a separate plot for reference ages 5, 10, 15, 24, 35, 45, 55, 65 and 75 years of age. The percentage of people aged 5, 10 and 15 testing positive for COVID-19 appears to have increased in the two weeks up to 20 March 2021. The percentage of young adults testing positive may be increasing, and the percentage of older adults testing positive may be decreasing.

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

In Scotland, the percentage of people testing positive for COVID-19 increased over the two weeks up to 20 March 2021. In England, the percentage of people testing positive for the coronavirus (COVID-19) is likely to have levelled off in the week ending 20 March 2021. In Wales, the percentage of people testing positive appeared level in the week ending 20 March 2021, although there is high uncertainty. In Northern Ireland, the percentage of people testing positive appeared to have remained level in the week ending 20 March 2021, although there is high uncertainty.

Figure 4: Modelled daily estimates of the percentage of the population testing positive for COVID-19 in each of the four nations of the UK, between 7 February and 20 March 2021 including 95% credible intervals (see notes 2,3,4,5,6)

*Northern Ireland

The chart shows the modelled daily estimates of the percentage of the population testing positive for COVID-19 in Scotland, England, Wales and Northern Ireland between 7 February and 20 March 2021, including 95% credible intervals. Over the last two weeks, the percentage of people testing positive increased in Scotland. In the week ending 20 March the proportion testing positive appeared level in Wales, likely levelled off in England and appeared to remain level in Northern Ireland.

Table 1: Modelled estimates of the proportion of the population testing positive for COVID-19, and corresponding 95% credible intervals, between 14 and 20 March 2021 for the four nations of the UK (See notes 1,3,4,5)

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	0.30% (0.26% to 0.34%)	162,500 (143,200 to 183,100)	1 in 340 (1 in 380 to 1 in 300)
Northern Ireland	0.32% (0.17% to 0.52%)	5,800 (3,100 to 9,500)	1 in 320 (1 in 590 to 1 in 190)
Scotland	0.41% (0.30% to 0.54%)	21,500 (15,600 to 28,500)	1 in 240 (1 in 340 to 1 in 180)
Wales	0.22% (0.13% to 0.34%)	6,700 (3,900 to 10,400)	1 in 450 (1 in 780 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 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 0.16% and 0.38%.

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 0.38% (95% credible interval: 0.29% to 0.52%).

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 0.16% (95% credible interval: 0.11% to 0.22%).

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

Figure 5: Modelled estimates of the percentage of the population within each CIS sub-region who would have tested positive for COVID-19 in the week 14 to 20 March 2021 in the UK (See notes 3,7)

This map of the UK shows the percentage of the population of each CIS sub-region estimated to test positive in the week 14 to 20 March 2021. In Scotland, the percentage of the population testing positive for COVID-19 in four of the six CIS sub-regions was below 0.25%, and in the other two sub-regions, it was between 0.25% and 0.50%.

Number of new COVID-19 infections in Scotland

This week ONS have re-introduced estimates of incidence of PCR-positive cases using a new method based which is based on the positivity estimate. This gives the rate at which new positives occur, and subsequently become detectable, within the population. ONS previously published results for England from 13 July to 28 November 2020 using a previous method.

The new incidence method uses an estimate of the length of time for which an individual will test positive, based on modelling the time from first positive to first subsequent negative test in the survey. This estimate is used alongside the positivity model to produce an estimate. For more information on the new method of incidence please see the updated methods article on the ONS webpage.

The reference date used for the official estimates of incidence of PCR-positive cases is 10 days prior to the end of the positivity reference week. This is necessary as estimates later than this date are more likely to change as additional data is received.

In Scotland, during the week 7 to 13 March 2021, it is estimated that there were 4.13 new PCR-positive COVID-19 cases per 10,000 people per day (95% credible interval: 2.58 to 5.87). This equates to 2,200 new positive cases in Scotland per day (95% credible interval: 1,400 to 3,100). Incidence increased in the week 7 to 13 March 2021 in Scotland, although credible intervals are wide.

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 represent the official estimate. These indicative estimates are based on the new model and are presented in Figure 6 and 7 by the point estimates (blue circle) as official estimates.

Figure 6: Modelled daily estimates and official reported/ indicative estimates of incidence rates in Scotland between 7 February to 13 March 2021, including 95% credible intervals (see notes 2,4,5,6)

This chart shows modelled daily estimates, as well as official reported/ indicative estimates of incidence rates in Scotland from 7 February to 13 March 2021, including 95% credible intervals. Incidence increased in Scotland in the week 7 to 13 March 2021, although credible intervals are wide.

Figure 7: Official reported/ indicative estimates of incidence rates in Scotland between 25 October 2020 to 13 March 2021, including 95% credible intervals (see notes 4,5,6)

The chart shows all indicative/ official reported estimates of the percentage of incidence rates in Scotland between 25 October 2020 to 13 March 2021, including 95% credible intervals.

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.

The percentage testing positive compatible with the UK variant have likely levelled off in England in the week ending 20 March 2021. In Wales and Northern Ireland, the trend in the percentage testing positive compatible with the UK variant is uncertain. The percentage testing positive compatible with the UK variant have likely increased in Scotland in the week ending 20 March 2021.

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

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 71,893 swab tests from 30,549 people, with a total of 305 positive tests in 264 people from 219 households. In the latest two-week period, there were 17,396 swab tests from 15,821 people, with a total of 65 positive tests in 63 people from 49 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:

• Welsh Government
• Department of Health in Northern Ireland

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 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.
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

8. The first three official reported estimates on this chart, represented by pale blue markers, are 14-day weighted estimates rather than weekly modelled estimates. These 14-day weighted estimates are not directly comparable with the weekly modelled estimates due to the differing methodology, however they have been included in this chart as they were reported as the official estimates for Scotland before the weekly modelled estimates became available.