Longitudinal Study of the Signal Strength in two Serologic Assays for Detection of SARS-CoV-2 Specific Antibodies

Background: In the course of the current SARS-CoV-2 pandemic, antibody assays provide an important means for guidance of public health efforts. Thus, characterization of the course of antibody signals on different widely used assays is needed. Methods: We selected 25 PCR-confirmed SARS-CoV-2 cases among 3,273 healthcare workers and measured the course of the antibody signal using the Abbott Architect SARS-CoV-2 IgG assay and the Roche Elecsys (R) Anti-SARS-CoV-2 immunoassay. The signal strength was then modelled using linear mixed models adjusted for age. Results: Since first sampling, the assay signal decreased per day in the Abbott assay (standardized slope (beta) = -0.46, 95% CI = -0.54 to -0.39). In contrast, an increase in the signal was ascertained by the Roche immunoassay per day (beta = 0.25, 95% CI = 0.09 to 0.41). Conclusions: Roche Elecsys (R) Anti-SARS-CoV-2 immunoassay may exhibit greater sensitivity in detecting SARS-CoV-2-specific antibodies in individuals in late stages of postinfection.