Coronavirus (COVID-19): ONS Infection Survey – antibody data for Scotland – 18 May 2022

ONS Coronavirus (COVID-19) Infection Survey – Antibody Data – 18 May 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 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 subject to revision.

Main Points

In the week beginning 2 May 2022, the percentage of the adult (aged 16 years and above) population in Scotland who are estimated to have antibodies against SARS-CoV-2 at the 179 ng/mL threshold remained high, at 99.1% (95% credible interval: 98.7% to 99.3%).

The latest antibody estimates remained high across all age groups in Scotland.

Information on this release

The antibody estimates for the most recent week in this publication include data from 2 to 5 May 2022.

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

This week, we present the estimated percentage of adults with antibodies to SARS-CoV-2 at the 179 ng/mL level first introduced to these publications on 13 January 2022 (see note 11). The most recent data for the previously reported standard antibody threshold of 42 ng/mL (up to 3 April 2022) continues to be plotted in the figures.

In their previous release, the ONS introduced an additional antibody series based on a higher level of 800 ng/ml. This week, these estimates are subject to additional quality assurance and so have not been updated.

Antibody estimates for those aged under 16 in Wales, Northern Ireland and Scotland have also not been updated in this release as they are undergoing additional quality assurance.

Antibody data up to 17 April 2022 for the 800 ng/ml level and for those aged under 16 years in Wales, Northern Ireland and Scotland can be found in the reference tables on the ONS website.

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 2 May 2022, the percentage of the adult (aged 16 years and above) population in Scotland who are estimated to have antibodies against SARS-CoV-2 at the 179 ng/mL threshold remained high, at 99.1% (95% credible interval: 98.7% to 99.3%). 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. The series at the 42 ng/mL antibody level covers the period 7 December 2020 to 3 April 2022 and the series at the 179 ng/mL antibody level covers the period 7 December 2020 to 5 May 2022.

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 May 2022, including 95% credible intervals

   

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

In the latest week, 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. The series at the 42 ng/mL antibody level covers the period 7 December 2020 to 3 April 2022 and the series at the 179 ng/mL antibody level covers the period 7 December 2020 to 5 May 2022.

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 May 2022, including 95% credible intervals

   

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

In previous releases, the ONS have included antibody estimates for those aged under 16 in Wales, Northern Ireland and Scotland. These estimates have not been updated in this release as they are undergoing additional quality assurance.

Antibody data for those aged under 16 years in Wales, Northern Ireland and Scotland up to 17 April 2022 can be found in the reference tables on the ONS website.

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 sampling method for Northern Ireland is different to the other nations, inviting only people that have previously participated in a Northern Ireland Statistics and Research Agency (NISRA) survey, which could result in a sample of individuals that are more likely to get vaccinated. This should be taken into consideration if comparing antibody estimates across the four nations, since vaccine status and antibody positivity are related.
9. 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.
10. The previously reported standard antibody threshold of 42 ng/mL was determined prior to the development of COVID-19 vaccinations. As the pandemic and vaccinations have evolved, the ONS have reviewed the way that it presents information about antibody levels and introduced two new thresholds: 179 ng/mL and 800 ng/mL (see notes 11 & 12).
11. 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.
12. In the release on 4 May 2022, the ONS introduced the 800 ng/mL antibody threshold. This threshold level has been chosen solely based on the test result data to provide historic estimates and is not based on any evidence on the level of antibodies needed for protection against Omicron, as this evidence is not yet available. The ONS may update the level used in antibody tests if research shows that an alternative level would identify changes in antibody levels earlier (antibody levels greater than 800ng/ml are currently under investigation).
13. The test used for spike antibodies measures their concentration in ng/ml. The previously reported standard antibody threshold of 42 ng/mL corresponds to 23 binding antibody units (BAU)/mL using the World Health Organisation’s standardised units (enabling comparison across different antibody assays). This is the threshold that the test is CE marked against and approved by the Medicines and Healthcare products Regulatory Agency, providing greater than 99% sensitivity and specificity in identifying people who have had a COVID-19 infection before (“natural immunity”) from people who have not. The antibody level of 179 ng/ml corresponds to 100 BAU/ml, and 800 ng/ml to 447 BAU/ml.
14. 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.