REACT Study: Coronavirus Antibody Prevalence Falling in England

Credit Imperial College London

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Ten weeks ago, in Imperial College London: (REACT) SARS-CoV-2 Antibody Prevalence Study - England,  we looked at initial data coming from 100,000 home antibody test kits distributed throughout the UK by Imperial College London in conjunction with the NHS between June 20th and July 13th.

These home test kits were described last August in a ICL news article called Biggest study on antibody finger-prick tests identifies promising kits by Justine Alford, which found the test had a high specificity (98.6%), and moderate sensitivity (84%). 

In other words, the test reliably detects antibodies 84% of the time and correctly identified the absence of antibodies 98.6% of the time.  When combined with its ease of use, this test was selected for the antibody prevalence study. 

Highlights of this study's findings include:

1. Roughly 6% of the UK Population had likely been infected with SARS-CoV-2
2. Highest rates of infection were detected in London
3. People of Black or Asian (mainly South Asian) ethnicity were most affected
4. 1/3rd of positive cases were reported as asymptomatic.
5. An infection fatality ratio of 0.90%

Fast forward to today and we have a new analysis from this REACT study - this time involving more than 365,000 test results collected through the end of September - that finds the level of detectable antibodies in the UK has dropped since the first round of tests, suggesting (as have other studies, see below) that some COVID-19 cases lose antibodies against the virus fairly quickly after infection. 

A few of the many recent studies on declining post-infection antibody levels against COVID-19 include:

EID Journal: Waning Antibody Response In Asymptomatic and Symptomatic SARS-CoV-2 Infection

Nature Medicine: Seasonal Coronavirus Protective Immunity Is Short-Lasting

EID Journal: Antibody Profiles According to Mild or Severe SARS-CoV-2 Infection

CDC Clarifies: Recovered COVID-19 Cases Are Not Necessarily Immune To Reinfection

Kings College: Longitudinal Evaluation & Decline of Antibody Responses in SARS-CoV-2 infection

Declining antibodies raise concerns over the potential for reinfection with the virus, and over just how long protection from a vaccine might last. The level and duration of antibody detection appears to correlate with disease severity, with milder cases declining faster than severe cases.

It should be noted however, that nAb titers aren't the only measure of potential post-infection immunity, as the role of T-Cells and other elements of the innate immune system in fighting this virus remain poorly understood.

Although one would expect the percentage of COVID-positive antibody tests in the UK to continue to rise, today's REACT analysis reveals that a second round of testing (in August & September) found more than a 25% drop in positive antibody tests across the UK.

First stop, a link and some excerpts from the abstract of the pre-print study from researchers at Imperial College London and the NHS, followed by a press report from Imperial College London.  Follow the links to read both in their entirety.

Declining prevalence of antibody positivity to SARS-CoV-2: a community study of 365,000 adults

 Helen Ward1,4,5*, Graham Cooke2,4*, Christina Atchison1,4, Matthew Whitaker1, Joshua Elliott1, Maya Moshe2 , Jonathan C Brown2 , Barney Flower2,4, Anna Daunt2,4, Kylie Ainslie1,5, Deborah Ashby1, Christl Donnelly1,6, Steven Riley1,5, Ara Darzi3,4, Wendy Barclay2,†, Paul Elliott1,4,7,8,9† for the REACT study team.

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.

(SNIP)

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.

(Continue . . . ) 

Coronavirus antibody prevalence falling in England, REACT study shows

by Justine Alford 27 October 2020

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%.

Our study shows that over time there is a reduction in the proportion of people testing positive for antibodies. It remains unclear what level of immunity antibodies provide, or for how long this immunity lasts. - Prof Paul Elliott study author, Imperial College London

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 available in a pre-print report and will 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.”

(Continue . . . ) 

 

While elevated antibody levels against SARS-CoV-2 are presumed to represent some degree of immunity against reinfection - no one knows how protective they really are - or what antibody titer is required to reliably prevent reinfection.  

This observed rapid decline in antibody levels with SARS-CoV-2 is consistent, however, with what we've seen with other human coronaviruses (hCoVs), which appear capable of reinfecting individuals every year or two.

Although the jury is still out, the evidence continues to suggest that anyone counting on post-infection `herd immunity' to end this pandemic quickly may be severely disappointed.  It is also not known whether vaccine induced immunity will prove more durable than via natural infection. 

Nearly 11 months into COVID-19, and there are still more questions than answers.