Coronavirus (COVID-19): ONS Infection Survey – antibody data for Scotland – 29 June 2022

ONS Coronavirus (COVID-19) Infection Survey – Antibody Data – 29 June 2022

The COVID-19 Infection Survey aims to measure:

• how many people across England, Wales, Northern Ireland and Scotland test positive for a COVID-19 infection at a given point in time, regardless of whether they report experiencing symptoms
• the average number of new positive test cases per week over the course of the study
• the number of people who test positive for antibodies

The regular reporting of Covid-19 Infection Survey (CIS) data for Scotland on the Scottish Government website will stop after the 1 July 2022, making this the last of our articles about antibody positivity. The latest antibody positivity estimates for England, Wales, Northern Ireland and Scotland will continue to be available in the ONS bulletins and datasets on the ONS website. If you have any feedback on this change please contact covidinfectionsurvey@gov.scot.

We would like to thank those who have read and used these articles in their personal and professional lives, and provided feedback on its format and content.

All results are provisional and subject to revision.

Main Points

In the week beginning 30 May 2022, the percentage of the adult (aged 16 years and above) population in Scotland estimated to have antibodies against SARS-CoV-2 at or above the level of 179 nanograms per millilitre (ng/ml) remained high, at 97.2% (95% credible interval: 96.7% to 97.6%).

In the same week, antibody positivity in adults (aged 16 years and above) has continued to remain high across all age groups in Scotland.

In the same week, in Great Britain, the percentage of children (aged 8 to 15 years) estimated to have antibodies against SARS-CoV-2 at or above the level of 179 ng/ml was high, at 95.5% for children aged 12 to 15 years (95% credible interval: 92.1% to 97.4%), and 72.9% for children aged 8 to 11 years (95% credible interval: 62.8% to 81.5%).

Information on this release

The antibody positivity estimates for the most recent week in this publication include data from 30 May to 5 June 2022.

As the COVID-19 pandemic and vaccinations have evolved, the ONS has reviewed how it presents information about antibody levels (see note 2).

The ONS has made several improvements to its antibody modelling, including to better account for changes in the sample dilution used in the antibody tests. This has resulted in some small changes to the antibody positivity estimates since they were last updated. However, recent trends have not been affected by these changes.

The ONS has become aware of an issue with antibody laboratory results from 28 January to 3 March 2022. As a result, all estimates over this period are subject to change due to the re-processing of some results.

This week, following these changes, we present weekly antibody positivity estimates at or above the antibody level of 179 ng/ml for those aged 16 years and above by age group. We also report weekly antibody positivity estimates for those aged 8 to 15 years for Great Britain (England, Wales and Scotland) as a whole by age group

The ONS has not reported antibody positivity estimates at or above the 42 ng/ml level since the release on 20 April 2022 because all age groups have been at or nearly at 100% antibody positivity at or above 42 ng/ml for some time. Positivity estimates at or above the 800 ng/ml level were produced for the release on 4 May 2022, but have not been updated due to additional development taking place on these statistics. In this release, the ONS has removed the previously published 42 ng/ml level data and 800 ng/ml level data from the dataset. Estimates at or above the 42 ng/ml and 800 ng/ml levels in previous datasets are therefore not comparable with estimates at or above the 179 ng/ml level in this release.

In this publication, the following terminology is used:

• Antibodies - the ONS measures the levels of antibodies in people who live in private households to understand who has had COVID-19 in the past and the impact of vaccinations. It takes between two and three weeks after infection or vaccination for the body to make enough antibodies to fight the infection. Antibodies can help prevent individuals from getting the same infection again. Once infected or vaccinated, antibodies remain in the blood at low levels and can decline over time.
• SARS-CoV-2 - this is the scientific name given to the specific virus that causes COVID-19.

All COVID-19 Infection Survey estimates are subject to uncertainty, given that a sample is only part of the wider population, so caution should be taken in interpreting the results.

The ONS blog on antibodies and immunity, gives further information on the link between antibodies and immunity and the vaccine programme. Further information on methodology can be found in the notes at the end of this release and in the COVID-19 Infection Survey methodology article.

Antibody estimates: likelihood of testing positive for antibodies against SARS-CoV-2

In the week beginning 30 May 2022, the percentage of the adult (aged 16 years and above) population in Scotland estimated to have antibodies against SARS-CoV-2 at or above the level of 179 ng/ml remained high, at 97.2% (95% credible interval: 96.7% to 97.6%). Please see note 7 for information on credible intervals.

Modelled weekly estimates of the percentage of the adult population testing positive for coronavirus (COVID-19) antibodies, from a blood sample, are displayed in Figure 1 as estimates for week beginning date, showing the trend over time.

Figure 1: Modelled weekly percentage of the adult population testing positive for antibodies to SARS-CoV-2 at or above 179 ng/ml, 7 December 2020 to 5 June 2022, including 95% credible intervals (see notes 3,11,12)

    

Antibody estimates by age group for adults (aged 16 years and above): likelihood of testing positive for antibodies against SARS-CoV-2

In the week beginning 30 May, antibody positivity in adults (aged 16 years and above) has continued to remain high across all age groups in Scotland.

Modelled weekly estimates of the percentage of the adult population testing positive for coronavirus (COVID-19) antibodies, from a blood sample, by age group, are displayed in Figure 1 as estimates for week beginning date, showing the trend over time.

Figure 2: Modelled weekly percentage of the adult population testing positive for antibodies to SARS-CoV-2 at or above 179 ng/ml by age group, 7 December 2020 to 5 June 2022, including 95% credible intervals  (see notes 3,11,12)

    

Antibody estimates by age group for children (aged 8 to 15 years): likelihood of testing positive for antibodies against SARS-CoV-2

In the week beginning 30 May, in Great Britain, the percentage of children (aged 8 to 15 years) estimated to have antibodies against SARS-CoV-2 at or above the level of 179 ng/ml was high, at 95.5% for children aged 12 to 15 years (95% credible interval: 92.1% to 97.4%), and 72.9% for children aged 8 to 11 years (95% credible interval: 62.8% to 81.5%).

Modelled weekly estimates of the percentage of children testing positive for coronavirus (COVID-19) antibodies, from a blood sample, by age group, are displayed in Figure 1 as estimates for week beginning date, showing the trend over time.

Figure 3: Modelled weekly percentage of the child population in Great Britain testing positive for antibodies to SARS-CoV-2 at or above 179 ng/ml by age group, 29 November 2021 to 5 June 2022, including 95% credible intervals (see notes 3,11,12,13)

Methodology and further information

1. Further information on methodology can be found in the COVID-19 Infection Survey methodology article.
2. Antibody positivity is defined by having a fixed concentration of antibodies in the blood. Most people who are vaccinated will retain higher antibody levels than before vaccination but may have a lower number of antibodies than the threshold at the time of testing. A negative test result occurs if there are no antibodies, or if antibody levels are too low to reach a threshold at the time of testing. Therefore, a negative result does not necessarily mean that a person has no antibodies or immune protection.
3. The analysis on antibodies in this bulletin is based on blood test results taken from a randomly selected subsample of individuals aged 8 years and over who live in private households. The survey excludes those in hospitals, care homes and other communal establishments. This can be used to identify individuals who have had the infection in the past or have developed antibodies as a result of vaccination.
4. It is important to draw the distinction between testing positive for antibodies and having immunity. A person’s immune response does not rely on the presence of antibodies alone. It is not yet known how having detectable antibodies, now or at some time in the past, affects the chance of becoming infected with or experiencing symptoms, as other parts of the immune system will offer protection. A person’s ‘T cell’ response will provide protection but is not detected by blood tests for antibodies. Immune response is affected by a number of factors, including a person’s health conditions and age. Additional information on the link between antibodies and immunity and the vaccine programme can be found in the ONS blog on antibodies and immunity.
5. More information about the COVID-19 Infection Survey in Scotland can be found on the information page on the Scottish Government website, and previous COVID-19 Infection Survey data for Scotland can be found in this collection.
6. 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 wider interval indicates more uncertainty in the estimate.
7. The latest week’s modelled estimate is subject to more uncertainty as it is an incomplete week of data and therefore more likely to change when more data become available.
8. The weekly modelled estimates use standard calendar weeks starting on a Monday. To provide the most timely and accurate estimates possible for antibody positivity, the model will include data for the first four to seven days of the week, depending on the availability of test results.
9. In the release on 13 January 2022, the ONS introduced the 179 ng/mL antibody threshold. Research by academic partners identified this threshold as providing a 67% lower risk of getting a new COVID-19 infection with the Delta variant after two vaccinations with either Pfizer or AstraZeneca vaccines. The 179 ng/mL antibody threshold was determined from analysis during the period when most COVID-19 infections were with the Delta variant. It is likely that the equivalent level of protection for the Omicron variant will require a different antibody threshold.
10. The test used for spike antibodies measures their concentration in ng/ml. The antibody level of 179 ng/ml corresponds to 100 binding antibody units (BAU)/ml, using the WHO standardised units (enabling comparison across different antibody assays).
11. The denominators used for antibodies are the total for each age group in the sample at that particular time point, then post-stratified by the mid-year population estimate.
12. The ONS has become aware of an issue with antibody laboratory results from 28 January to 3 March 2022. As a result, all estimates over this period are subject to change due to the re-processing of some results.
13. Estimates for children in age groups 8 to 11 years and 12 to 15 years are not available before 29 November 2021.