Coronavirus (COVID-19) Infection Survey, antibody data, UK: 24 August 2022

In this bulletin, we report percentages of the population that are estimated to have antibodies against SARS-CoV-2, the specific virus that causes coronavirus (COVID-19) above two levels: a 179 ng/ml level and an 800 ng/ml level.

In the week beginning 18 July 2022, the percentage of people estimated to have antibodies against SARS-CoV-2:

• in England, was 96.1% of adults at or above 179 ng/ml (95% credible interval: 95.6% to 96.6%), and 73.6% of adults at or above 800 ng/ml (95% credible interval: 72.0% to 75.2%)

• in Wales, was 95.7% of adults at or above 179 ng/ml (95% credible interval: 94.6% to 96.6%), and 73.8% of adults at or above 800 ng/ml (95% credible interval: 70.9% to 76.5%)

• in Northern Ireland, was 94.7% of adults at or above 179 ng/ml (95% credible interval: 91.8% to 96.6%), and 75.3% of adults at or above 800 ng/ml (95% credible interval: 69.8% to 80.2%)

• in Scotland, was 95.5% of adults at or above 179 ng/ml (95% credible interval: 94.5% to 96.4%), and 73.5% of adults at or above 800 ng/ml (95% credible interval: 70.9% to 75.9%)

• in Great Britain: at or above 179 ng/ml, was 72.6% of children aged 8 to 11 years (95% credible interval: 59.8% to 82.3%) and 90.3% of children aged 12 to 15 years (95% credible interval: 84.3% to 94.1%); at or above 800 ng/ml, was 41.1% of children aged 8 to 11 years (95% credible interval: 29.0% to 53.4%) and 74.9% of children aged 12 to 15 years (95% credible interval: 66.9% to 81.4%).

Estimates of antibodies against SARS-CoV-2 at the 800 ng/ml level are not comparable with our estimates published before 27 July 2022 because of method changes since our 4 May 2022 publication: Coronavirus (COVID-19) Infection Survey, antibody data, UK: 4 May 2022.  In our previous publication we included information about the recent methods and processing changes: Coronavirus (COVID-19) Infection Survey, antibody data, UK: 27 July 2022

In the week beginning 18 July 2022, the percentage of the adult population estimated to have antibodies against SARS-CoV-2 at or above the level of 179 nanograms per millilitre (ng/ml) remained high across the UK. Among the oldest age groups, the percentage estimated to have antibodies against SARS-CoV-2 at or above the level of 800 ng/ml has generally increased since April 2022, likely as a result of fourth vaccinations given to people of those ages.

Figure 1: The percentage of the population estimated to have antibodies against SARS-CoV-2 remained high for UK adults in the week beginning 18 July 2022

Modelled percentage of the adult population with levels of antibodies against SARS-CoV-2 at or above 179 nanograms per millilitre (ng/ml) or 800 ng/ml, by age group, UK countries, 7 December 2020 to 24 July 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. There was an issue with antibody lab results over the period 10 January to 27 February 2022 which primarily impacted 800 ng/ml estimates. As a result, 800 ng/ml level estimates are not available for this period, and all other estimates for February 2022 are subject to change because of the re-processing of some results.
7. For 16- to 24-year-olds in Northern Ireland, central estimates are not shown for the most recent two-week period. This is because of low sample sizes during the move to remote data collection. The overall accuracy of trends is unaffected.

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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 positivity estimates for the most recent week in this publication include data from 18 July to 24 July 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 level 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 179 nanograms per millilitre (ng/ml) level is based on research by our academic partners, and reflects the percentage of adults who would have been likely to have a strong enough antibody response to provide some protection from getting a new COVID-19 infection with the Delta variant. This level is higher than our previously reported standard level of 42 ng/ml which was associated with SARS-CoV-2 infection before vaccines became available. Antibody levels below this 179 ng/ml level does not mean that a person has no antibodies or immune protection at all. This antibody level 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 level will provide equivalent protection against the Omicron variant, and we will keep the level used in our analysis of antibodies under regular review. The 800 ng/ml level is the highest level at which we can produce a historic back-series, and is provided to enable enhanced monitoring of antibody levels and waning. It is not based on academic research on protection against Omicron, as sufficient evidence on this is not yet available.

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 World Health Organization's (WHO) standardised units (enabling comparison across different antibody assays).

Further information on antibody test levels, 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?