Coronavirus antibody prevalence falling in England — REACT study

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Tests on more than 365,000 people in England have shown that the antibody response to the virus that causes COVID-19 wanes over time. Led by Imperial College London, analysis of finger-prick tests carried out at home between 20 June and 28 September found that the number of people testing positive dropped by 26.5% across the study period, from almost 6% to 4.4%.

The downward trend was observed in all areas of the country and age groups, but not in health workers, which could indicate repeated or higher initial exposure to the virus, the authors suggest. The decline was largest in people aged 75 and above compared to younger people, and also in people with suspected rather than confirmed infection, indicating that the antibody response varies by age and with the severity of illness.

People in London had the highest proportion of positive tests across the country, at around twice the national average. Health and care workers, ethnic minority groups, and those living in deprived areas and large households also had the greatest burden of past infection.

These findings suggest that there may be a decline in the level of immunity in the population in the months following the first wave of the epidemic.

These findings from the Real Time Assessment of Community Transmission (REACT) study are to be submitted for peer-review.

Professor Paul Elliott, director of the programme at Imperial, said: “Our study shows that over time there is a reduction in the proportion of people testing positive for antibodies. Testing positive for antibodies does not mean you are immune to COVID-19. It remains unclear what level of immunity antibodies provide, or for how long this immunity lasts. If someone tests positive for antibodies, they still need to follow national guidelines including social distancing measures, getting a swab test if they have symptoms and wearing face coverings where required.”

The REACT study is using finger-prick testing to detect coronavirus antibodies in the blood. When present these indicate that a person has been previously infected with the virus. The testing kits, called Lateral Flow Tests, detect antibodies above a particular concentration in the blood, and do not measure the amount of antibodies in a particular person.

The tests are sent out to randomly-selected adult volunteers across the country to carry out at home.

The latest report includes findings from three rounds of testing carried out over a three-month period. There were 17,576 positive results across all three rounds, around 30% of whom did not report any COVID-19 symptoms. After accounting for the accuracy of the test, confirmed by laboratory evaluation, and the country’s population characteristics, the study found that antibody prevalence declined from 6.0% to 4.8% and then 4.4% over the three months.

This was found across all ages but the smallest drop was found in the youngest age group, aged 18-24, falling from 7.9% to 6.7% (14.9%), while the largest was found in the oldest group, aged 75 and above, declining from 3.3% to 2.0% (39%).

Professor Helen Ward, one of the lead authors of the report said: “This very large study has shown that the proportion of people with detectable antibodies is falling over time. We don’t yet know whether this will leave these people at risk of reinfection with the virus that causes COVID-19, but it is essential that everyone continues to follow guidance to reduce the risk to themselves and others.”

All parts of the country showed a fall in prevalence, except the West Midlands which increased in round two and then declined in round three. London has maintained the highest prevalence of antibodies across the different rounds, with 9% testing positive in round three, compared with the South West which consistently had the smallest proportion.

The decline was largest in people who didn’t report a history of COVID-19, dropping by almost two-thirds (64.0%) between rounds one and three, compared to a decrease of 22.3% in people who had an infection confirmed by lab testing.

Health Minister Lord Bethell said: “This study led by Imperial and Ipsos MORI is a critical piece of research, helping us to understand the nature of COVID-19 antibodies over time, and improve our understanding about the virus itself. We rely on this kind of important research to inform our continued response to the disease, so we can continue to take the right action at the right time.

“It is also important that everyone knows what this means for them – this study will help in our fight against the virus, but testing positive for antibodies does not mean you are immune to COVID-19.

“Regardless of the result of an antibody test, everyone must continue to comply with government guidelines including social distancing, self-isolating and getting a test if you have symptoms and always remember Hands, Face, Space.”

A separate arm of the REACT study is using at-home swab tests to monitor levels of current infection, involving more than 150,000 people each month.

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.

Kelly Beaver, MD of public affairs at Ipsos MORI said: “Over 365,000 members of the public have volunteered to take part in this at home antibody study which involves a small finger-prick test. I’d like to thank all of those that took the time to participate in the study which provides another piece of information to help the Government manage the pandemic for us all.”

Abstract
Background: The prevalence and persistence of antibodies following a peak SARS-CoV-2 infection provides insights into its spread in the community, the likelihood of reinfection and potential for some level of population immunity.
Methods: Prevalence of antibody positivity in England, UK (REACT2) with three cross-sectional surveys between late June and September 2020. 365104 adults used a self-administered lateral flow immunoassay (LFIA) test for IgG. A laboratory comparison of LFIA results to neutralization activity in panel of sera was performed.
Results: There were 17,576 positive tests over the three rounds. Antibody prevalence, adjusted for test characteristics and weighted to the adult population of England, declined from 6.0% [5.8, 6.1], to 4.8% [4.7, 5.0] and 4.4% [4.3, 4.5], a fall of 26.5% [-29.0, -23.8] over the three months of the study. There was a decline between rounds 1 and 3 in all age groups, with the highest prevalence of a positive result and smallest overall decline in positivity in the youngest age group (18-24 years: -14.9% [-21.6, -8.1]), and lowest prevalence and largest decline in the oldest group (75+ years: -39.0% [-50.8, -27.2]); there was no change in antibody positivity between rounds 1 and 3 in healthcare workers (+3.45% [-5.7, +12.7]). The decline from rounds 1 to 3 was largest in those who did not report a history of COVID19, (-64.0% [-75.6, -52.3]), compared to -22.3% ([-27.0, -17.7]) in those with SARS-CoV-2 infection confirmed on PCR. Waning immunity 261020 3
Discussion: These findings provide evidence of variable waning in antibody positivity over time such that, at the start of the second wave of infection in England, only 4.4% of adults had detectable IgG antibodies using an LFIA. Antibody positivity was greater in those who reported a positive PCR and lower in older people and those with asymptomatic infection. These data suggest the possibility of decreasing population immunity and increasing risk of reinfection as detectable antibodies decline in the population.

Authors
Helen Ward, Graham Cooke, Christina Atchison, Matthew Whitaker, Joshua Elliott, Maya Moshe, Jonathan C Brown, Barney Flower, Anna Daunt, Kylie Ainslie, Deborah Ashby, Christl Donnelly, Steven Riley, Ara Darzi, Wendy Barclay, Paul Elliott for the REACT study team.

 

World Health Organisation spokesperson Tarik Jasarevic said that uncertainty over how long immunity would last and the fact most people had never had antibodies against the coronavirus in the first place showed the need to break transmission chains. “Acquiring this collective immunity just by letting virus run through the population is not really an option,” he is quoted in Reuters as saying.

Imperial’s study, based on a survey of 365,000 randomly selected adults, was released as a pre-print paper, and has not yet been peer-reviewed.

The rapid waning of antibodies did not necessarily have implications for the efficacy of vaccine candidates currently in clinical trials, Imperial’s Barclay said. “A good vaccine may well be better than natural immunity,” she said.

 

Imperial College London material

 

MedRxiv abstract (not peer reviewed)

 

Full Reuters report

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