Coronavirus (COVID-19) Infection Survey, antibody data for the UK: 16 March 2021

• In England, an estimated 1 in 3 people, or 34.6% of the population (95% confidence interval: 34.0% to 35.3%), would have tested positive for antibodies against the coronavirus - SARS-CoV-2 - on a blood test in the 28 days up to 3 March 2021, suggesting they had the infection in the past or have been vaccinated.

• In Wales, an estimated 1 in 3 people (95% confidence interval: 1 in 4 to 1 in 3) would have tested positive for antibodies against SARS-CoV-2 on a blood test in the 28 days up to 3 March 2021, suggesting they had the infection in the past or have been vaccinated.

• In Northern Ireland, an estimated 1 in 3 people (95% confidence interval: 1 in 4 to 1 in 3) would have tested positive for antibodies against SARS-CoV-2 on a blood test in the 28 days up to 3 March 2021, suggesting they had the infection in the past or have been vaccinated.

• In Scotland, an estimated 1 in 4 people (95% confidence interval: 1 in 5 to 1 in 4) would have tested positive for antibodies against SARS-CoV-2 on a blood test in the 28 days up to 3 March 2021, suggesting they had the infection in the past or have been vaccinated.

• The percentage of people testing positive for COVID-19 antibodies was higher for those aged 70 years and over in England, Wales and Scotland.

In this article, we refer to the presence of antibodies to the coronavirus (COVID-19) within the community population; community in this instance refers to private residential households, and it excludes those in hospitals, care homes and/or other institutional settings.

This article presents analysis on past infection and/or vaccination - which we define as testing positive for antibodies to SARS-CoV-2 for England, Wales, Northern Ireland and Scotland - based on findings from the Coronavirus (COVID-19) Infection Survey in the UK.

SARS-CoV-2 is the scientific name given to the specific virus that causes COVID-19. More information on our headline estimates of the overall number of positive cases of COVID-19 in England, Wales, Northern Ireland and Scotland are available in our latest bulletin.

Our last publication of antibodies data was 2 March for the 28-day period to 11 February 2021. Earlier antibodies data are available as part of a series of articles on the characteristics of those testing positive for COVID-19. To make the antibodies data and analysis easier to find, all releases from 3 February 2021 onwards are published in this Coronavirus (COVID-19) Infection Survey: antibody data for the UK article series.

Our methodology article provides further information around the survey design, how we process data and how data are analysed. The study protocol specifies the research for the study. Further information on what the analysis covers is provided at the start of each section.

About this analysis

The analysis in this article is based on blood test results taken from a randomly selected subsample of individuals aged 16 years and over, which are used to test for antibodies against SARS-CoV-2. This can be used to identify individuals who have had the infection in the past or have developed antibodies as a result of vaccination.

It takes between two and three weeks after infection or vaccination for the body to make enough antibodies to fight the infection. Antibodies remain in the blood at low levels, although these levels can decline over time to the point that tests can no longer detect them. Having antibodies can help to prevent individuals from getting the same infection again.

We measure the presence of antibodies to understand who has had the coronavirus (COVID-19) in the past and the impact of vaccinations. Once infected or vaccinated, the length of time antibodies remain at detectable levels in the blood is not fully known. It is also not yet known how having detectable antibodies, now or at some time in the past, affects the chance of getting COVID-19 again.

We present weighted estimates for 28-day periods of antibody positivity for England, Wales, Northern Ireland and Scotland, which allows us to provide fortnightly updates on antibody data. The 28-day periods presented in this analysis are updated to work backwards from the most recent 28-day period available. This means the time periods overlap with those presented in previous articles.

We also present the weighted estimates of antibody positivity for regions of England, and broken down by age and by sex for each of the UK countries. In addition, we present estimates of antibody positivity by age and sex combined for England and for the first time for Wales, Northern Ireland and Scotland.

In England, an estimated 34.6% (95% confidence interval: 34.0% to 35.3%) of the population would have tested positive for antibodies to SARS-CoV-2 from a blood sample in the 28 days up to 3 March 2021. The estimate is weighted to be representative of the overall population and suggests that an average of 15.6 million people aged 16 years and over in England would have tested positive for antibodies to SARS-CoV-2 during this time (95% confidence interval: 15.3 million to 15.8 million). This equates to 1 in 3 people aged 16 years and over (95% confidence interval: 1 in 3 to 1 in 3).

In Wales, an estimated 30.5% of the population would have tested positive for antibodies to SARS-CoV-2 from a blood sample (95% confidence interval: 27.5% to 33.6%) in the 28 days up to 3 March 2021. It is estimated that an average of 773,000 people aged 16 years and over in Wales would have tested positive for antibodies during this time (95% confidence interval: 697,000 to 852,000). This equates to 1 in 3 people aged 16 years and over (95% confidence interval: 1 in 4 to 1 in 3).

In Northern Ireland, an estimated 31.2% of the population would have tested positive for SARS-CoV-2 from a blood sample (95% confidence interval: 27.3% to 35.2%) in the 28 days up to 3 March 2021. It is estimated that an average of 463,000 people aged 16 years and over in Northern Ireland would have tested positive for antibodies during this time (95% confidence interval: 405,000 to 523,000). This equates to 1 in 3 people aged 16 years and over (95% confidence interval: 1 in 4 to 1 in 3).

In Scotland, an estimated 22.3% of the population would have tested positive for antibodies to SARS-CoV-2 from a blood sample (95% confidence interval: 20.6% to 24.1%) in the 28 days up to 3 March 2021. It is estimated that an average of 996,000 people aged 16 years and over in Scotland would have tested positive for antibodies during this time (95% confidence interval: 918,000 to 1.1 million). This equates to 1 in 4 people aged 16 years and over (95% confidence interval: 1 in 5 to 1 in 4).

Weighted estimates of the percentage of people testing positive for SARS-CoV-2 antibodies for 28-day periods in England, Wales, Northern Ireland and Scotland are presented in Figure 1. Across all four UK countries, the estimates suggest there has been an increase in antibody positivity in the most recent 28-day period.

Figure 1: In the 28 days up to 3 March 2021, the percentage of people testing positive for COVID-19 antibodies increased across all four UK countries

Estimated percentage of people testing positive for antibodies to SARS-CoV-2 from a blood sample, by 28-day periods, 30 April 2020 to 3 March 2021, UK

Notes:

1. All results are provisional and subject to revision.
2. These statistics refer to infections reported in the community, by which we mean private households. These figures exclude infections reported in hospitals, care homes and/or other institutional settings.
3. Survey fieldwork for the pilot study began in England on 26 April 2020. In Wales, fieldwork began on 29 June, in Northern Ireland fieldwork began on 26 July and in Scotland fieldwork began on 21 September.

Download the data

The analysis in this section uses data taken from the 28 days up to 3 March 2021 to produce weighted antibodies estimates.

There is some variation in antibody positivity between regions, from 39.4% (95% confidence interval: 37.7% to 41.1%) in the North West compared with 29.1% (95% confidence interval: 27.4% to 30.9%) in the South West.

Figure 2: COVID-19 antibody positivity was highest in the North West, London, and the West Midlands

Estimated percentage of people testing positive for antibodies to SARS-CoV-2 from a blood sample in the 28 days up to 3 March 2021, England

Notes:

1. All results are provisional and subject to revision.
2. These statistics refer to infections reported in the community, by which we mean private households. These figures exclude infections reported in hospitals, care homes and/or other institutional settings.

Download the data

The analysis in this section uses data taken from the 28 days up to 3 March 2021 to produce weighted antibody estimates by age in England, Wales, Northern Ireland and Scotland.

In England, the highest percentages of people testing positive for antibodies were for those aged 80 years and over at 75.7% (95% confidence interval: 73.0% to 78.2%), followed by people aged 75 to 79 years (68.8%, 95% confidence interval: 66.5% to 71.0%) and aged 70 to 74 years (54.7%, 95% confidence interval: 52.9% to 56.5%). The percentage of people testing positive for antibodies is lower for those aged under 70 years, ranging from 27.4% to 32.0%.

While there were 75.7% of people aged 80 years and over testing positive for antibodies in England, this figure relates to the community population who live in private households. Therefore, people in this age group who live in establishments such as care homes are not included in this survey. Because this group was the priority for receiving vaccinations, the true figure among those aged 80 years and over in the population may be different. An estimated 90% of people aged 80 years and over live in private households and 10% live in other establishments such as care homes.

In Wales, the highest percentages of people testing positive for antibodies were for those aged 80 years and over at 62.2% (95% confidence interval: 45.8% to 76.7%), those aged 75 to 79 years at 58.2% (95% confidence interval: 46.9% to 68.9%) and those aged 70 to 74 years at 47.1% (95% confidence interval: 39.1% to 55.2%). The percentage of people testing positive for antibodies was lower for those aged under 70 years, ranging from 20.0% to 27.4%.

In Northern Ireland, the percentage of people aged 70 years and over testing positive for antibodies was 44.4% (95% confidence interval: 34.7% to 54.3%). Because of small sample sizes, this analysis uses different age groups to England and other devolved administration antibodies analysis, with everyone over the age of 70 years included in the same age group. The percentage of people aged 25 to 34 years testing positive for antibodies was 22.9% (95% confidence interval: 13.7% to 34.5%).

In Scotland, the highest percentages of people testing positive for antibodies were for those aged 80 years and over at 60.9% (95% confidence interval: 50.3% to 70.8%), followed by people aged 75 to 79 years (39.8%, 95% confidence interval: 31.7% to 48.2%) and aged 70 to 74 years (38.9%, 95% confidence interval: 33.1% to 44.9%). The percentage of people testing positive for antibodies is lower in those aged under 70 years, ranging from 14.8% to 21.1%.

The higher levels of antibodies observed in older age groups reflect the high vaccination rate in older people. However, the percentage of people testing positive for antibodies varies by age group between nations. This could be explained by the varying approaches to vaccine distribution in different nations. This survey does not include those that live in care homes, one of the priority groups identified by the Joint Committee on Vaccination and Immunisation (JCVI). Daily and weekly counts of vaccine doses administered by nation can be seen in the Public Heath England (PHE) dashboard.

Figure 3: The percentage of people testing positive for COVID-19 antibodies was higher for those aged 70 years and over in England, Wales and Scotland

Estimated percentage of people testing positive for antibodies to SARS-CoV-2 from a blood sample, by age, in the 28 days up to 3 March 2021, UK

Notes:

1. All results are provisional and subject to revision.
2. These statistics refer to infections reported in the community, by which we mean private households. These figures exclude infections reported in hospitals, care homes and/or other institutional settings.
3. In Northern Ireland, the number of people sampled who tested positive for antibodies to SARS-CoV-2 is low compared with England, Wales and Scotland; therefore, people over the age of 70 years are included in the same age group.

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The analysis in this section presents modelled daily estimates of antibody positivity by single year of age for England, Wales, Northern Ireland and Scotland. The modelled data are produced using a different method to the 28-day weighted estimates presented in Section 5 and so they cannot be compared.

Figure 4 shows the percentages testing positive for COVID-19 antibodies by single year of age from 7 January to 3 March 2021 for each of the four UK countries.

Figure 4: The percentages testing positive for COVID-19 antibodies by single year of age in England, Wales, Northern Ireland and Scotland

Modelled estimated percentage of people testing positive for antibodies to SARS-CoV-2 from a blood sample, by single year of age, from 7 January to 3 March 2021, UK

Notes:

1. All results are provisional and subject to revision.
2. These statistics refer to infections reported in the community, by which we mean private households. These figures exclude infections reported in hospitals, care homes and/or other institutional settings.
3. The method used to generate the data differs from the 28-day weighted estimates of antibody positivity by age and so is not comparable.

Download the data

The analysis in this section uses data taken from the 28 days up to 3 March 2021 to produce weighted antibody estimates by sex in England, Wales, Northern Ireland and Scotland.

The percentage of people testing positive for antibodies was higher for females than males in England, Wales and Scotland. Differences between males and females in Northern Ireland were less certain because of wide confidence intervals. Possible reasons for these differences are that there are more females in occupation groups prioritised for vaccine, more females work in roles that may have exposed them to previous infection (such as personal caring services) or a biological reason (other research on immune responses and sex found that antibody responses to seasonal influenza vaccines are consistently at least twice as strong in females than males).

Figure 5: More females than males tested positive for COVID-19 antibodies in England, Wales and Scotland

Estimated percentage of people testing positive for antibodies to SARS-CoV-2 from a blood sample, by sex, in the 28 days up to 3 March 2021, UK

Notes:

1. All results are provisional and subject to revision.
2. These statistics refer to infections reported in the community, by which we mean private households. These figures exclude infections reported in hospitals, care homes and/or other institutional settings.

Download the data

The analysis in this section uses data taken from the 28 days up to 3 March 2021 to produce weighted antibody estimates by age and sex in England, Wales, Northern Ireland and Scotland. Because the number of people sampled who tested positive for antibodies to SARS-CoV-2 in Wales, Northern Ireland and Scotland is low compared with England, age groups are driven by sample size and differ between countries.

In England, Wales and Scotland, the percentage of people testing positive for antibodies was higher for females than males, and this was broadly consistent within the different age groups. Differences between males and females in Northern Ireland were less certain because of wide confidence intervals, but the pattern is likely to be the same.

Figure 6: In England, Wales and Scotland, the percentage of people testing positive for antibodies was higher for females than males, and this was broadly consistent within the different age groups

Estimated percentage of people testing positive for antibodies to SARS-CoV-2 from a blood sample, by age and sex, in the 28 days up to 3 March 2021, UK

Notes:

1. All results are provisional and subject to revision.
2. These statistics refer to infections reported in the community, by which we mean private households. These figures exclude infections reported in hospitals, care homes and/or other institutional settings.
3. Age groups are driven by sample size and differ between countries.

Download the data

The Coronavirus (COVID-19) Infection Survey analysis was produced by the Office for National Statistics (ONS) in partnership with the University of Oxford, the University of Manchester, Public Health England and Wellcome Trust. Of particular note are:

• Sarah Walker - University of Oxford, Nuffield Department for Medicine: Professor of Medical Statistics and Epidemiology and Study Chief Investigator
• Koen Pouwels - University of Oxford, Health Economics Research Centre, Nuffield Department of Population Health: Senior Researcher in Biostatistics and Health Economics
• Thomas House - University of Manchester, Department of Mathematics: Reader in mathematical statistics

Acknowledgements

The authors would like to thank the following individuals, which include both external collaborators and internal ONS teams, and acknowledge their contribution made to these articles:

University of Oxford - Sarah Walker, Koen Pouwels

ONS Methodology - Katie Davies, Gareth James, Camille Harrison

ONS COVID-19 Infection Survey coding and analysis data processing teams - Heledd Thomas, Lina Lloyd, Antonio Felton, Petya Kozhuharova, Alex Jaggs

ONS COVID-19 Infection Survey dissemination team - Hannah Donnarumma, Byron Davies, Zoë Willis, Alice McTiernan, Kyle Knights, George Feldman

Confidence interval

A confidence interval gives an indication of the degree of uncertainty of an estimate, showing the precision of a sample estimate. The 95% confidence intervals are calculated so that if we repeated the study many times, 95% of the time, the true unknown value would lie between the lower and upper confidence limits. A wider interval indicates more uncertainty in the estimate. Overlapping confidence intervals indicate that there may not be a true difference between two estimates.

For more information, see our methodology page on statistical uncertainty.