Coronavirus (COVID-19) Infection Survey, antibody data, UK: 20 April 2022

The following statistics show the percentage of the population that are estimated to have antibodies against SARS-CoV-2, the specific virus that causes coronavirus (COVID-19).

In the week beginning 28 March 2022, the percentage of the population that were estimated to have antibodies against SARS-CoV-2 at or above a threshold of 179 nanograms per millilitre (ng/ml) was:

• in England, 98.9% of the adult population (95% credible interval: 98.6% to 99.1%)
• in Wales, 98.8% of the adult population (95% credible interval: 98.4% to 99.1%)
• in Northern Ireland, 99.2% of the adult population (95% credible interval: 98.7% to 99.6%)
• in Scotland, 99.0% of the adult population (95% credible interval: 98.6% to 99.2%)
• across the UK, the percentages for children ranged from 95.3% to 97.6% for those aged 12 to 15 years and from 83.7% to 85.9% for those aged 8 to 11 years

In the week beginning 28 March 2022, the percentage of the adult population estimated to have antibodies against SARS-CoV-2 at or above a threshold of 179 nanograms per millilitre (ng/ml) remained high across all regions of England. Regional data and percentages of the population who are estimated to have antibodies at or above the previously reported antibody threshold of 42 ng/ml, and the higher antibody threshold of 179 ng/ml, can be found in our Coronavirus (COVID-19) antibody data for the UK dataset.

Figure 1: The percentage of the population who are estimated to have antibodies against SARS-CoV-2 remained high for those aged 8 years and over across the UK in the week beginning 28 March 2022

Modelled percentage of the population with levels of antibodies against SARS-CoV-2 at or above a threshold of 179 nanograms per millilitre (ng/ml), by age group, UK countries, 7 December 2020 to 3 April 2022

Notes:

1. All results are provisional and subject to revision.

2. These statistics refer to antibody tests for individuals living in private households.

3. In Northern Ireland, the number of people 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 are estimated to have antibodies against SARS-CoV-2 at or above a threshold of 179 ng/ml.

7. Estimates for children aged 8 to 15 years are not available before 29 November 2021.

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Antibodies

We measure the levels 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. 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.

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 include data from 28 March to 3 April 2022.

Our Coronavirus (COVID-19) Infection Survey: methodology article provides further information around the survey design, how we process data, and how data are analysed. Our 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 and 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.

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 on 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 on research by our academic partners, and it is 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. This threshold is higher than our previously reported standard threshold of 42 ng/ml and will provide earlier signs of any changes in antibody levels. 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. We may update the threshold used in our antibody tests if research shows that an alternative threshold would identify changes in antibody levels earlier.

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).

Further information on antibody test thresholds, and the link between antibodies and infections can be found in our recent blog post: Relationship between COVID-19 infections and antibodies: What do the data show?