Comparative evaluation of in-house ELISA and two commercial serological assays for the detection of antibodies against SARS-CoV-2

The in-house ELISA SARS-CoV-2 serological assay, developed by the Armauer Hansen Research Institute (AHRI) in Ethiopia, measures anti-SARS-CoV-2 receptor binding domain (RBD) antibodies. This study aimed to compare the performance of our cost-effective in-house ELISA with two established commercially available SARS-CoV-2 antibody detection assays during the pre-Omicron COVID-19 pandemic. In April 2021, serum samples were collected from 1441 students across 60 schools in Oromia, from 15 hotspot districts and towns. Socio-demographic data were gathered using CSentryCSProDataEntry7.2.1. Performance agreements between AHRI's in-house ELISA and the two commercial assays were analyzed in these serum samples. Statistical analyses, including Cohen's kappa (κ), overall percentage agreement, positive percent agreement (PPA), and negative percent agreement (NPA), were performed using STATA software. Diagnostic parameters were presented with 95% confidence intervals (CI), calculated using the Clopper-Pearson method. The performance comparison of the in-house ELISA showed substantial agreement with the two commercial assays. The overall concordance rate between in-house ELISA and Elecsys CLIA was 80.8% (95% CI 75.0-86.5), while the agreement between in-house ELISA and the Rapid LFA test (IgG + IgM) was 75.8% (95% CI 70.1-81.5). The kappa coefficients were: in-house ELISA vs. Elecsys CLIA (κ = 0.61, 95% CI 0.55-0.67), in-house ELISA vs. Rapid LFA test (IgG + IgM) (κ = 0.52, 95% CI 0.46-0.58), and Elecsys CLIA vs. Rapid LFA test (IgG + IgM) (κ = 0.73, 95% CI 0.67-0.78). The in-house ELISA demonstrated strong agreement with the Elecsys CLIA, showing a PPA of 81.7% and an NPA of 80.1%. Compared to the Rapid LFA test (IgG + IgM), which had a PPA of 83% and an NPA of 70.4%, the in-house ELISA exhibited better overall agreement with Elecsys CLIA. This study's findings indicate substantial agreement between the in-house ELISA and Elecsys. However, only modest agreement was observed between the in-house ELISA and the rapid test (IgG + IgM). Together, these results suggest the utility of the in-house ELISA as a cost-effective tool for sero surveillance studies and monitoring the effect of interventions in resource-poor settings.