Comparative evaluation of SARS-CoV-2 IgG assays in India

Abstract

Introduction IgG immunoassays have been developed and used widely for clinical samples and serosurveys for SARS-CoV2, with most detecting antibodies against the spike/receptor-binding-domain or nucleocapsid. Limited information is available on comparative evaluation of IgG immunoassays against a clinical reference standard, i.e., RT-PCR positivity with >20 days of illness. This study addresses the need for comparing clinical performance of IgG immunoassays with respect to this alternate reference standard. Methods We compared the performance of three immunoassays, an in-house RBD assay, and two commercial assays, the Diasorin LIAISON SARS-CoV-2 S1/S1 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 panel of sera. 379 sera and plasma samples from RTPCR positive individuals >20 days of illness in symptomatic or RT-PCR positivity in asymptomatic individuals and 184 samples collected prior to 2019 were used for assay evaluation. Results The sensitivity of the assays were 84.7 (95 %CI 80.6–88.1), 82.6 (95 %CI 78.3–86.2) and 75.7 (95 %CI 71.0–79.9) 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 positive sera/plasma than Kavach. Conclusion Independent comparisons support the evaluation of performance characteristics of immunoassays. All three assays are suitable for serosurveillance studies, but in low prevalence sites, estimation of exposure may require adjustment based on our findings.

Evaluation of Antibody Response in Symptomatic and Asymptomatic COVID-19 Patients and Diagnostic Assessment of New IgM/IgG ELISA Kits

“…AnshLabs IgG ELISA attained the highest sensitivity within the first two weeks of sampling (78.2%), while Lionex achieved the highest sensitivity after one month (96.6%). This indicates a very good performance for the evaluated IgG ELISA tests, particularly Lionex, compared to other automated assays such as Roche Elecsys (sensitivity of 97.2%), Abbot (sensitivity of 92.7%) [32], and DiaSorin (sensitivity of 95.0%) [33]. Previous studies reported slightly better IgG sensitivity results for EDI and DiaPro; 76.1% vs. 82.7% for EDI and 53.5% vs. 92.2% for DiaPro [34].…”

A Prospective Study on Rapidly Declining SARS‐CoV‐2 IgG Antibodies Within One to Three Months of Testing IgG Positive: Can It Lead to Potential Reinfections?

“…Serology testing helps us in retrospectively determining previous SARS-CoV-2 infections in people who have not been tested earlier by an RT-PCR. While most detect specific antibodies against the spike/receptor-binding-domain or nucleocapsid [2], limited commercial availability of approved kits to assess neutralizing antibodies against the virus [3] has restricted the wider use for accurate testing of neutralizing antibody titers.…”

Community prevalence of antibodies to SARS-CoV-2 and correlates of protective immunity in an Indian metropolitan city

“…To estimate the association between seroprevalence and incidence of new cases post survey we performed a linear regression for the incidence of new cases, adjusting for the reported incidence at the beginning of the survey. We did not adjust prevalence for imperfect test sensitivity, since there is currently no gold standard for comparison and as the sensitivity of the assay used compared favourably with other assays 15 .…”

“…Serum was separated using standard methods and stored in multiple aliquots. The in-house THSTI RBD-IgG ELISA was performed using methods previously described 15 . We assumed that the IgG antibodies are detectable 14-21 days post-infection and that these antibodies persist, following infection, for four months 4,16,17 .…”