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® 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 (ß) = -0.46, 95% CI = -0.54 to -0.39). In contrast, an increase in the signal was ascertained by the Roche immunoassay per day (ß = 0.25, 95% CI = 0.09 to 0.41). CONCLUSIONS: Roche Elecsys® Anti-SARS-CoV-2 immunoassay may exhibit greater sensitivity in detecting SARS-CoV-2-specific antibodies in individuals in late stages of postinfection.

Prevalence of Severe Acute Respiratory Syndrome Coronavirus-2-specific Antibodies in German Blood Donors during the COVID-19 Pandemic.

BACKGROUND: Coronavirus disease-2019 (COVID-19) is a respiratory infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While RT-PCR assays are used routinely to diagnose active COVID-19, serological testing offers a means of identifying individuals who previously experienced asymptomatic infections, as well as those who experienced symptomatic infections but no longer carry the virus. METHODS: The presence of SARS-CoV-2 IgG-positive antibodies in the sera of 673 blood donors residing in south-western Germany before and 3,880 donors after the advent of the COVID-19 pandemic was determined and confirmed using two highly sensitive serological tests. RESULTS: Approximately 0.40% of the donors assessed during the COVID-19 pandemic possessed SARS-CoV-2 IgG-positive antibodies, decidedly fewer than the percentage of SARS-CoV-2-infected individuals determined by real-time RT-PCR nationwide. CONCLUSIONS: These findings confirm the efficacy serological testing in identifying asymptomatic COVID-19 patients.