SARS-CoV-2 Antibody Testing in Healthcare Workers: a comparison of the clinical performance of three commercially available antibody assays

Allen, N.; Brady, M.; Carrion Martin, A. I.; Domegan, L.; Walsh, C.; Houlihan, E.; Kerr, C.; Doherty, L.; King, J.; Doheny, M.; Griffin, D.; Molloy, M.; Dunne, J.; Crowley, V.; Holmes, P.; Keogh, E.; Naughton, S.; O'Rourke, F.; Kelly, M.; Lynagh, Y.; Crowley, B.; De Gascun, C.; Holder, P.; Bergin, C.; Fleming, C.; Ni Riain, U.; Conlon, N.

SARS-CoV-2 antibodies are an excellent indicator of past COVID-19 infection. As the COVID-19 pandemic progresses, retained sensitivity over time is an important quality in an antibody assay that is to be used for the purpose of population seroprevalence studies. We compared 5788 healthcare worker (HCW) serum samples on two serological assays (Abbott SARS-CoV-2 anti-nucleocapsid IgG and Roche Anti-SARS-CoV-2 anti-nucleocapsid Total Antibody) and a subset of samples (all Abbott assay positive or grayzone, n=485) on Wantai SARS-CoV-2 anti-spike Antibody ELISA. For 367 samples from HCW with previous PCR-confirmed SARS-CoV-2 infection we correlated the timing of infection with assay results. Overall seroprevalence was 4.2% on Abbott, 9.5% on Roche. Of those with previously confirmed infection, 41% (150/367) and 95% (348/367) tested positive on Abbott and Roche respectively. At 21 weeks (150 days) after confirmed infection, positivity on Abbott started to decline. Roche positivity was retained for the entire study period (33 weeks). Factors associated (P[≤] 0.050) with Abbott seronegativity in those with previous PCR-confirmed infection included sex (male OR0.30;95%CI0.15-0.60), symptom severity (OR0.19 severe symptoms;95%CI0.05-0.61), ethnicity (OR0.28 Asian ethnicity;95%CI0.12-0.60) and time since PCR diagnosis (OR2.06 for infection 6 months previously;95%CI1.01-4.30. Wantai detected all previously confirmed infections. In our population, Roche detected antibodies up to at least seven months after natural infection with SARS-CoV-2. This may indicate that Roche is better suited than Abbott to population-based studies. Wantai demonstrated high sensitivity but sample selection was biased. The relationship between serological response and functional immunity to SARS-CoV-2 infection needs to be delineated.