Coronavirus (COVID-19) Infection Survey, antibody data, UK: 23 February 2022

The following statistics are the percentage of the population that would have tested positive on a blood test for antibodies against SARS-CoV-2, the specific virus that causes coronavirus (COVID-19), above a threshold of 179ng/ml. This threshold is higher than our previously reported standard threshold of 42 ng/ml, reflecting having had the virus in the past or having been vaccinated. This higher threshold will provide the earliest signs of any changes in antibody levels. Today, we have published new data that show:

• In England, 98.2% of the adult population (95% credible interval: 97.9% to 98.4%) are estimated to have antibodies against SARS-CoV-2 at the 179 ng/ml threshold, in the week beginning 31 January 2022.

• In Wales, 97.9% of the adult population (95% credible interval: 97.4% to 98.3%) are estimated to have antibodies against SARS-CoV-2 at the 179 ng/ml threshold, in the week beginning 31 January 2022.

• In Northern Ireland, 98.2% of the adult population (95% credible interval: 97.3% to 98.8%) are estimated to have antibodies against SARS-CoV-2 at the 179 ng/ml threshold, in the week beginning 31 January 2022.

• In Scotland, 98.2% of the adult population (95% credible interval: 97.8% to 98.5%) are estimated to have antibodies against SARS-CoV-2 at the 179 ng/ml threshold, in the week beginning 31 January 2022.

• Across the UK, the percentage of children who are estimated to have antibodies against SARS-CoV-2 at the 179 ng/ml threshold ranged from 91.7% to 95.1% for those aged 12 to 15 years and from 72.2% to 82.0% for those aged 8 to 11 years, in the week beginning 31 January 2022.

Coronavirus (COVID-19) vaccination estimates for adults are modelled separately to our estimates for children and require additional quality assurance. Therefore, adult vaccination estimates have not been updated in this publication and will be reintroduced as soon as possible. Updated children vaccination estimates can be found in the accompanying dataset. Official government figures on vaccinations are available.

Figure 1: The percentage of the population who would have tested positive for antibodies against SARS-CoV-2 remained high for those aged 16 and over across the UK in the week beginning 31 January 2022

Modelled percentage of the population with levels of antibodies to SARS-CoV-2 at or above the higher antibody threshold, by age group, UK countries, 7 December 2020 to 4 February 2022

Notes:

1. All results are provisional and subject to revision.
2. These statistics refer to antibody tests for individuals living in private households. The figures exclude individuals in hospitals, care homes and/or other communal establishments.
3. In Northern Ireland, the number of adults sampled is low compared with England, Wales and Scotland; therefore, adults aged 50 to 69 years are included in the same age group, and those aged 70 years and over are included in the same age group.
4. All estimates are subject to uncertainty, given that a sample is only part of the wider population. A credible interval gives an indication of the uncertainty of an estimate from data analysis.
5. 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.
6. Estimates show the percentage of the population who would have tested positive for antibodies against SARS-CoV-2 at or above an antibody threshold of 179 ng/ml. This is a higher threshold than our previously reported standard threshold of 42 ng/ml, which will show any changes in antibody levels earlier.

Download the data

In the week beginning 31 January 2022, the percentage of adults who would have tested positive for antibodies against SARS-CoV-2 at an antibody threshold of 179 ng/ml remained high across all regions of England. Regional data and percentages of the population who would have tested positive at the previously reported standard antibody threshold of 42 ng/ml, can be found in the accompanying dataset.

These results have been published as a shortened release because of consistently high levels of antibody positivity among all age groups across the UK. For a more detailed description of our statistics, please refer to our previous publication.

Antibodies

We measure the presence of antibodies in people who live in private households to understand who has had coronavirus (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. If they do get infected, people with antibodies are less likely to have severe symptoms. Once infected or vaccinated, antibodies remain in the blood at low levels and can decline over time. The length of time antibodies remain at detectable levels in the blood is not fully known.

SARS-CoV-2

This is the scientific name given to the specific virus that causes COVID-19.

Credible interval

A credible interval gives an indication of the uncertainty of an estimate from data analysis. A 95% credible interval is calculated so that there is a 95% probability of the true value lying in the interval.

Reference dates

The antibody estimates for the most recent week in this publication includes data from 31 January to 4 February 2022. The estimates for the number of coronavirus (COVID-19) vaccinations reported in those under 16 years of age for the most recent week in this publication includes data from 24 to 30 January 2022. Modelled vaccination estimates for adults for England, Wales, Northern Ireland and Scotland require additional quality assurance and have not been updated in our bulletin this time.

Our methodology article provides further information around the survey design, how we process data, and how data are analysed. The Quality and Methodology Information explains the strengths and limitations of the data, methods used, and data uses and users.

More information on measuring the data is available in the Coronavirus (COVID-19) Infection Survey statistical bulletin.

Survey data

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 or other communal establishments. The blood samples are used to test for antibodies against SARS-CoV-2.

Antibodies and immunity

Antibody positivity is defined by having a fixed concentration of antibodies in the blood. 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. It does not mean that their antibody level is at zero or that a person has no protection against COVID-19. Additionally, there are other parts of the immune system that will offer protection, for example, a person's T-cell response. This will not be detected by blood tests for antibodies. A person's immune response is affected by a number of factors, including health conditions and age.

Equally, antibody levels are expected to decrease over time irrespective of vaccination or natural infection, especially when exposure to the virus is reduced. This is because our bodies stop making antibodies when they are not needed.

Our blog on antibodies and immunity gives further information on the link between antibodies and immunity and the vaccine programme. Our blog on vaccine effectiveness provides information on the effectiveness of vaccinations against Alpha and Delta variants, which is based upon the research conducted by partners from the University of Oxford.

Measuring antibody positivity

Our antibody threshold is currently 179 nanograms per millilitre (ng/ml). This threshold is based upon research by our academic partners, and used to determine the percentage of adults who are likely to have a strong enough antibody response to provide some protection from getting a new COVID-19 infection. Antibody levels below this threshold do not mean that a person has no antibodies or immune protection at all.

This antibody threshold was identified 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, compared with someone who was unvaccinated and had not had COVID-19 before. It is unlikely that this threshold will provide equivalent protection against the Omicron variant and we will keep the threshold used in our analysis of antibodies under regular review.

The test used for spike antibodies measures their concentration in ng/ml. The antibody threshold of 179 ng/ml corresponds to 100 binding antibody units (BAU)/ml using the World Health Organization's (WHO) standardised units (enabling comparison across different antibody assays).

Vaccination estimates

While the daily official government figures provide the recorded actual numbers of vaccines against SARS-CoV-2 issued, our vaccination estimates are likely to be different from the official figures. This is because they are estimates based on a sample survey of reported vaccine status and are provided for context alongside our antibodies estimates. For further information regarding our approach to calculating vaccination estimates, please refer to our methodology article.