LIMIT of DETECTION of SARS-CoV-2 ANTIBODY ASSAYS

ABSTRACT

Background: Seroprevalence studies of antibodies to SARS-CoV-2 are important for public health surveillance. Recent studies have shown that antibodies to SARS-CoV-2, both from natural infection and vaccination, decrease with time from exposure. Variation in the performance of antibody assays will impact the estimates of SARS-CoV-2 exposure and vaccination levels in a population. Using standardized serial dilutions, we evaluated 17 SARS-CoV-2 assays to establish an approximate limit of detection for each assay. Methods: The evaluated assays consisted of three chemiluminescent immunoassays (CLIAs), eight standard enzyme-linked immunosorbent assays (ELISAs), and six lateral flow assays (LFAs). All assays either evaluated IgG antibodies or total antibodies to SARS-CoV-2. The target antigen of 14 assays was the spike protein (S) or receptor binding domain (RBD);three assays evaluated antibodies to the nucleocapsid protein (N). A human SARS-CoV-2 serology standard with a WHO SARS-CoV-2 Serology International Standard binding antibody units (BAU) value of 764 BAU/mL to spike IgG and 681 BAU/mL to nucleocapsid IgG was obtained from the Frederick National Laboratory for Cancer Research. Half-logarithmic serial dilutions of the standard were then run in triplicate on each assay. Results: The MSD V-Plex chemiluminescent immunoassays (CLIAs) were the most sensitive by three logs, with positive results at a dilution greater than 1106 (Figure). Standard ELISAs were less sensitive, with limits of detection ranging from dilutions of 120 (Euroimmun NeutraLISA) to 11620 (Euroimmun SARS-CoV-2 IgG and Euroimmun QuantiVac). Lateral flow assays (LFAs) were the least sensitive, with only one assay (Wondfo Colloidal Gold) having at least one positive result with a dilution greater than 1180. Conclusion: As population seroprevalence to SARS-CoV-2 continues to rise, tests with a high limit of detection will be crucial for surveillance studies. As antibody levels decline after vaccination or infection, our data indicate that CLIAs like the MSD assay may provide the best opportunity to capture asymptomatic cases and individuals with low antibody titers.