Performance Assessment of First-Generation Anti-SARS-CoV-2 Serological Assays

The clinical and epidemiological use of SARS-CoV-2 antibody assays is under debate with urgent need to validate and verify the performance of SARS-CoV-2 serologic assays. We aim to assess the clinical and analytical performance of three commercial serological assays of SARS-CoV-2, comparing three anti-SARS-CoV-2-IgG ELISA and identifying the seroconversion and seroprevalence in our population.

A cross sectional study conducted from April 2020 to July 2020 at National Institute of Blood disease and Bone Marrow Transplantation Karachi, Pakistan with sample size of 404, enrolled consecutively. Participants were categorized into four groups’ namely convalescent plasmadonors (CPDs n=239), health care professionals (HCPs n=44), healthy blood donors (HBDs n=70) and from community (n=51).

We evaluated the performance of Elecsys anti-SARS-CoV-2 electrochemiluminescence (ECLIA) assay on Cobas-e411 by Roche, three qualitative anti-SARS-CoV-2-IgG enzyme linked imunosorbant assay (ELISA) by (Generic assays, Euroimmun & Omega diagnostics), one quantitative ELISA assay by AESKU Diagnostics and two immune chromatography(ICT) kits namely InstaTest™ by CORTEZ and TEST IT by TURKLAB.

From total 404 subjects, 322 (83.5%) were males. Mean age was 36.79±11.95 years. Among 239 in CPDs group, 202(84.5%) showed positive antibodies by ECLIA. The qualitative anti-SARS-CoV-2 IgG ELISA was positive in 174 (72.8%) and quantitative IgG in 180(75.3%) with mean titer of 56.7 ±39.7 U/ml. Sensitivity and specificity of ECLIA were 97.44& 99%, ELISA by Generic assays were 67.85% and 89.9%; Euroimmun had 90.38% and 94.9%; Omega Diagnostics 96.4% and 95% and the AESKULISA 93.75% and 100% respectively. Seroconversion was found to be 53.8% and 77.77% within 7 -8 days and 12 to 14 days post onset of symptoms respectively. ICT had more specificity but less sensitivity. Seroprevalence was found to be 84.5%, 40.9% and 21.4% in CPDs, HCPs and HBDs respectively.

The Roche ECLIA, qualitative ELISA by Omega Diagnostics & Euroimmun showed higher sensitivity as well as higher specificity. Quantitative ELISA has higher specificity and relatively high sensitivity. Significant numbers of COVID patients do not have detectable antibodies by all assays.