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 national research programme supported by staff at Imperial College Healthcare NHS Trust.

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 and the first findings provide an initial insight in to trends in infection across the country.

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.

The first findings to be published from the study, which have been submitted for peer review, suggest that slightly under 6% of the population may have antibodies for the virus by the end of June – an estimated 3.4 million people. The presence of antibodies indicates that they were likely to have previously been exposed to Covid-19. London had the highest number of people with antibodies, at over twice the national average (13 per cent), while the South West had the lowest (3 per cent).

To develop a reliable and accurate antibody test for the study, researchers assessed 11 different tests for accuracy and ease of use at home. Around 300 staff from Imperial College Healthcare NHS Trust who previously had a postitive PCR swab test initially volunteered to trial the different tests to assess how easy they were to use and their accuracy. These volunteers also donated a blood sample which was analysed in the laboratory using a test developed by Imperial researchers.

The team went on to carry 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.

The best performing test was then rolled out to a nationally-representative sample of 100,000 members 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.

Whilst it is currently unknown whether having antibodies to the virus provides immunity against getting Covid-19 again, understanding trends in past cases, and how these vary by geography and demographics, will help guide local public health responses. It will also help identify groups who may be at increased risk and inform actions to control the disease. All REACT study participants are asked to continue to follow Government guidelines, regardless of their result.

Professor Graham Cooke, consultant in infectious diseases at the Trust and research lead at Imperial College, 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.”

The study findings also show that the overall infection fatality ratio - the proportion of infected people who died - was calculated to be 0.9 per cent, similar to other countries such as Spain.

Antibodies were found in almost all (96 per cent) of those tested who had a previous infection confirmed by a PCR swab test. People who had severe symptoms from the disease were twice as likely to have antibodies as those with no symptoms when they were diagnosed with or suspected of having COVID-19 (29 per cent vs 14 per cent). The highest numbers of positive antibody results were in people who reported confirmed or suspected Covid-19 in March and April, and were shown across all regions of England.

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 more likely to have had Covid-19 compared to white people.

Evidence of antibodies were found in more than 16 per cent of care home workers with client-facing roles and 12 per cent of healthcare professionals that have direct patient contact. In non-key workers, the rate was around 5 per cent.

For Black, Asian and other ethnicity individuals, the rates of positive results were 17 per cent, 12 per cent and 12 per cent, respectively, compared to 5 per cent 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 per cent) 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 per cent).

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 per cent) compared to those from the least deprived (5 per cent). 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 per cent vs 5 per cent).

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.

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.”

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.”

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.”