Largest study on home coronavirus antibody testing publishes first findings

More than 100,000 people across England have tested themselves for SARS-CoV-2 antibodies at home as part of a major research programme.

Led by Imperial College London, the REACT (REal Time Assessment of Community Transmission) study is using antibody finger-prick tests to track past infections and monitor the progress of the pandemic. It’s the first nation-wide antibody surveillance study to be rolled out across England using self-testing at home.

"Using the finger-prick tests suitable for large scale home testing has given us clearest insight yet into the spread of the virus in the country and who has been at greatest risk." Prof Graham Cooke NIHR Research Professor of Infectious Disease, Imperial College London

The findings, published in Nature Communications, show that slightly under 6% of the population had antibodies to the virus and had likely previously had COVID-19 by the end of June, an estimated 3.4 million people. London had the highest numbers at over twice the national average (13%), while the South West had the lowest (3%).

Key workers in care homes and health care were among those most likely to have already been infected with the coronavirus. And Black, Asian and minority ethnic (BAME) individuals were between two and three times as likely to have had COVID-19 compared to white people.

Understanding trends in past cases, and how these vary by geography and demographics, will help guide local public health responses, identify groups who may be at increased risk and inform actions to control the disease.

Professor Graham Cooke, NIHR Research Professor of Infectious Diseases and research lead at Imperial, said: “There are still many unknowns with this new virus, including the extent to which the presence of antibodies offers protection against future infections. Using the finger-prick tests suitable for large scale home testing has given us clearest insight yet into the spread of the virus in the country and who has been at greatest risk. These data will have important implications for decisions around ongoing control measures in England.”

REACT has been commissioned by the Department of Health and Social Care, and is being carried out in partnership with Imperial College London, Imperial College Healthcare NHS Trust and Ipsos MORI.

Differences in antibody prevalence

The overall infection fatality ratio - the proportion of infected people who died - was calculated to be 0.9%, similar to other countries such as Spain.

Antibodies were found in almost all (96%) of those who had a previous infection confirmed by a swab test. People who had severe symptoms from the disease were twice as likely to have antibodies than those with no symptoms when they were diagnosed with or suspected having COVID-19 (29% vs 14%).

The highest numbers of positive results were in people who reported confirmed or suspected COVID-19 March and April, and were shown across all regions of England. More than 16% of care home workers with client-facing roles and 12% of healthcare professionals that have direct patient contact tested positive. In non-key workers, the rate was around 5%.

For Black, Asian and other ethnicity individuals, the rates of positive results were 17%, 12% and 12%, respectively, compared to 5% for white individuals. The gap was reduced after the researchers took into account factors such as age and key worker status, but rates were still higher overall for BAME individuals. Other factors not explored in this study could therefore be behind the higher likelihood of previous infection in this group, such as transport use and behaviour.

Trends were also observed with age, where young people aged 18-24 had the highest rates (8%) and were more than twice as likely to test positive than older adults aged 65 to 74, who were least likely to have had the virus (3%).

In addition the researchers found links with deprivation and household size. People from the poorest areas were more likely to have had COVID-19 (7%) compared to those from the least deprived (5%). And people living in households of more than 7 people were more than twice as likely to have been infected than those living alone or with one other person (13% vs 5%).

Choosing the best antibody test

To select an antibody test for use in this nation-wide surveillance survey, Imperial researchers assessed 11 different tests for accuracy and ease of use. The team also carried out a large public engagement exercise with more than 14,000 people to improve usability of the tests, called Lateral Flow Tests (LFTs). LFTs are inexpensive and can be taken at home without a healthcare professional, making them well-suited for large-scale population studies where costly laboratory testing isn’t possible.

"Thanks to the contribution of tens of thousands of members of the public, we have been able to show how the virus which causes COVID-19 has spread across England." Prof Helen Ward Professor of Public Health

The best performing test was then rolled out to a nationally-representative sample of the public, who were randomly selected, between 20 June and 13 July. The tests use a drop of blood from the finger and give a result in just 15 minutes, which participants read themselves and upload via an online survey.

Professor Helen Ward, lead author for the study of population prevalence from Imperial College London, said: “Thanks to the contribution of tens of thousands of members of the public, we have been able to show how the virus which causes COVID-19 has spread across England. We have shown that it is possible to do a large scale study with home tests, and this is an efficient way of improving our understanding.

"We found that people working in care homes and healthcare are at particularly high risk of being exposed to the virus, as are those from Black, Asian and other minority ethnic groups. We need to do far more to protect people from any future waves of infection.”

Professor Paul Elliott, senior study author from Imperial College London, said: “Finding out who has been infected by the virus, where and when is vital to be able to understand the pattern and extent of transmission in the community. This study gives a very detailed picture of the pandemic as it unfolded in England in the period prior to and during lockdown.”

Understanding coronavirus spread

As it is currently unknown whether having antibodies to the virus stops people from getting COVID-19 again, participants are asked to continue to follow Government guidelines, regardless of their result.

"The more information we can gather on this virus, and the easier we can make it for people to participate in these studies, the better equipped we will be to respond." Edward Argar Health Minister

Health Minister Edward Argar said: “Large scale antibody surveillance studies are crucial to helping us understand how the virus has spread across the country and whether there are specific groups who are more vulnerable, as we continue our work to drive down the spread of the disease. 

“We don’t yet know that antibodies provide immunity to coronavirus, but the more information we can gather on this virus, and the easier we can make it for people to participate in these studies, the better equipped we will be to respond. 

“The British public have already played a massive part in helping to keep the country safe and I’d urge them to consider signing up to one of the many vital surveillance studies taking place over the coming months as part of our national testing effort.”

The study will be repeated in autumn, testing 200,000 people, and research on the accuracy of different LFTs is ongoing to ensure that the best available test is used in the REACT programme as it continues.

Kelly Beaver, Managing Director – Public Affairs, Ipsos MORI said: “The thorough and rigorous work carried out by Imperial College London has allowed us to find a robust at home finger prick test for COVID-19 antibodies. This is the springboard for developing a far greater understanding of COVID-19 antibodies and how prevalent they are in the population through our large-scale antibody study, conducted with over 100,000 members of the public.”

Access the pre-print on medRvix here.