Comparative Evaluation of SARS-CoV-2 IgG Assays in India

IgG immunoassays have been developed and used widely for clinical samples and serosurveys for SARS-CoV-2. We compared the performance of three immunoassays, an in-house RBD assay, and two commercial assays, the Diasorin LIAISON SARS-CoV-2 IgG CLIA which detects antibodies against S1/S2 domains of the Spike protein and the Zydus Kavach assay based on inactivated virus using a well-characterized sera-panel. 379 sera/plasma samples from RT-PCR positive individuals >20 days of illness in symptomatic or RT-PCR positivity in asymptomatic individuals and 184 pre-pandemic samples were used. The sensitivity of the assays were 84.7, 82.6 and 75.7 respectively for RBD, LIAISON and Kavach. Kavach and the in-house RBD ELISA showed a specificity of 99.5% and 100%, respectively. The RBD and LIAISON (S1/S2) assays showed high agreement (94.7%;95%CI:92.0,96.6) and were able to correctly identify more positives than Kavach. All three assays are suitable for serosurveillance studies, but in low prevalence sites, estimation of exposure may require adjustment based on our findings.