SARS-CoV-2 antibody testing in UK: detectable IgG up to 20 weeks post infection

Louise J Robertson, Julie S Moore, Kevin Blighe, Kok Yew Ng, Nigel Quinn, Fergal Jennings, Gary Warnock, Peter Sharpe, Mark Clarke, Kathryn Maguire, Sharon Rainey, Ruth Price, William Burns, Amanda Kowalczyk, Agnes Awuah, Sara McNamee, Gayle Wallace, Steve Sager, Connie Chao Shern, M. Andrew Nesbit, James McLaughlin, Tara Moore

doi: https://doi.org/10.1101/2020.09.29.20201509

This article is a preprint and has not been certified by peer review [what does this mean?]. It reports new medical research that has yet to be evaluated and so should not be used to guide clinical practice.

PDF: https://www.medrxiv.org/content/10.1101/2020.09.29.20201509v1.full.pdf

Abstract

Background The SARS-CoV-2 pandemic necessitated rapid and global responses across all areas of healthcare, including an unprecedented interest in serological immunoassays to detect antibodies to the virus. The dynamics of the immune response to SARS-CoV-2 is still not well understood. Methods We measure SARS-CoV-2 antibody levels in plasma samples from 880 people in Northern Ireland by Roche Elecsys Anti-SARS-CoV-2 IgG/IgA/IgM, Abbott SARS-CoV-2 IgG and EuroImmun IgG SARS-CoV-2 ELISA immunoassays to analyse immune dynamics over time. Using these results, we develop a "pseudo gold standard" reference cohort against which to assess immunoassay performance. We report performance metrics for the UK-RTC AbC-19 rapid lateral flow immunoassay (LFIA) against a characterised panel of 304 positives established using the "pseudo gold standard" system and 350 negative samples. Results We detect persistence of SARS-CoV-2 IgG up to 140 days (20 weeks) post infection, across all three antibody immunoassays, at levels up to 4.4 times the cut-off for a positive result by Roche measurement. Using our "pseudo gold standard" cohort (n=348 positive, n=510 negative) we determine the sensitivity and specificity of the three commercial immunoassays used (EuroImmun; Sens. 98.9% [97.7-99.7%]; Spec. 99.2% [98.4-99.8%]; Roche; Sens. 99.4% [98.6-100%]; Spec. (96.7% [95.1-98.2%]; Abbott; Sens. 86.8% [83.1-90.2%]; Spec. (99.2% [98.4-99.8%]). The UK-RTC AbC-19 lateral flow immunoassay using shows a sensitivity of 97.70% (95.72%-99.34%) and specificity of 100% (100.00-100.00%). Conclusions Through comprehensive analysis of a large cohort of pre-pandemic and pandemic individuals, we show detectable levels of IgG antibodies, lasting up to 140 days, providing insight to immunity levels at later time points. We propose an alternative to RT-PCR positive status as a standard for assessing SARS-CoV-2 antibody assays and show strong performance metrics for the AbC-19 rapid test.

Competing Interest Statement

At the time of this study TM and JML acted as advisors to CIGA HealthCare, an industrial partner in the UK Rapid Test Consortium. No personal financial reward or renumeration was received for this advisory role. At the time of submission of this manuscript TM and JML no longer held these advisory positions. All other authors have no potential conflict of interest to report.

Funding Statement

Funding for this study was obtained from UK-RTC to cover all laboratory costs incurred.

https://www.medrxiv.org/content/10.1101/2020.09.29.20201509v1