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Evaluation of high-throughput SARS-CoV-2 serological assays in a longitudinal cohort of mild COVID-19 patients: sensitivity, specificity and association with virus neutralization test

Objectives: We evaluated widely-used SARS-CoV-2 serological tests and their potential association with virus neutralization test (VNT) in a cohort of mild COVID-19 patients. Methods: A total of 439 specimens were longitudinally collected from 76 healthcare workers with RT-PCR-confirmed mild COVID-19. Nine serological assays developed by leading global companies (Abbott, DiaSorin, Siemens, Bio-Rad, Wantai, bioMerieux, Euroimmun) were assessed. For each test the sensitivity to detect SARS-CoV-2 antibodies was determined weekly after symptom onset. Correlation and concordance were assessed using the Spearman and Cohen Kappa coefficients, respectively. Positive percent agreement and negative percent agreement (NPA) with the VNT were also determined. Results: The Wantai Total Ab assay targeting the receptor binding domain (RBD) within the S protein presented the best sensitivity at different times during the course of disease. The best correlation between antibody level and neutralizing antibody titer was found with the Euroimmun S1-based IgA assay (Spearman coefficient [95%CI]: 0.71 [0.61-0.79]). A moderate concordance (Kappa [95%CI]: 0.43[0.23-0.63]) as well as the lowest NPA (33%) was found between the Wantai Total Ab assay and the VNT. Compared to the Wantai Total Ab assay, other total Ab or IgG assays targeting the S or the RBD (bioMerieux, DiaSorin, Siemens,) were more concordant with the VNT (Kappa>0.7 for the three tests) and had a higher NPA (range: 90% to 97%). Conclusions: Although some assays presented a better concordance with VNT than others, the present findings emphasize that commercialized serological tests including those targeting the RBD cannot substitute VNT for the assessment of functional antibody response.