Abstract
WHO 20/136 is standard reference material for SARS-COV-2 serology assays. Standardization of serology assays that target the same antigen and class of immunoglobulin will enable comparison of results between studies that use various lab-developed and commercial assays around the world. Standardization of assays will help better define immune correlates of protection and possibly immune correlates of vaccine efficacy. Two automated SARS-COV-2 anti-S1 RBD immunoglobulin serology assays on the Atellica IM Analyzer were calibrated to WHO 20/136 Standard Reference Material which was assigned 1000 binding antibody units (BAU/mL). The anti-S1 RBD IgG assay (sCOVG) cut-off Index of 1.00 corresponded to WHO 45.1 BAU/mL, and the anti-S1 RBD Ig Total assay (COV2T) cut-off Index of 1.00 corresponded to WHO 6.70 BAU/mL.