Development and Evaluation of Two Rapid Indigenous IgG-ELISA immobilized with ACE-2 Binding Peptides for Detection Neutralizing Antibodies Against SARS-CoV-2

COVID-19 pandemic situation demands effective serological tests with a view to adopting and developing policy for disease management, determining protective immunity as well as for sero-epidemiological study. Our study aims to develop and evaluate two rapid in-house ELISA assays targeting neutralizing antibodies (IgG) against S1 subunit of spike in SARS-CoV-2 and Receptor Binding Domain (RBD), as well as comparative analysis with nucleocapsid (NCP) ELISA. The assays were conducted with 184 samples in three panels collected from 134 patients. Panel 1 and 2 consist of RT-PCR positive samples collected within two weeks and after two weeks of symptom onset, respectively. Negative samples are included in panel 3 from healthy donors and pre-pandemic dengue patients. The total assay time has been set 30 minutes for both of the ELISA assays. Results show that S1 and RBD ELISA demonstrates 73.68% and 84.21% sensitivities, respectively for samples collected within two weeks, whereas 100% sensitivities were achieved by both for samples that were collected after two weeks of the onset of symptoms. S1-ELISA shows 0% positivity to panel 3 while for RBD-ELISA the figure is 1%. A strong correlation (r _s =0.804, p<0.0001)) has been observed between these two assays. When compared with NCP-ELISA, S1 slightly better correlation (r _s =0.800, p<0.0001) than RBD (r _s =0.740, p<0.0001). Our study suggests S1-ELISA as more sensitive one than the RBD or nucleocapsid ELISA during the later phase of infection, while for overall sero-monitoring RBD specific IgG ELISA is recommended. Moreover, non-reactivity to dengue emphasize the use of these assays for serosurveillance of COVID-19 in the dengue endemic regions.