Z. S Mousa - Baghdad Veterinary Hospital, Baghdad, Iraq
A. S Abdulamir - Department of Medical Microbiology, College of Medicine, Al-Nahrain University, Baghdad, Iraq

The establishment of an approach for detecting the anti-severe acute respiratory syndrome coronavirus-۲ (SARS-CoV-۲)-receptor-binding domain (RBD) neutralizing antibodies (nAbs) by a safe, easy, and rapid technique without requiring the use of live viruses is essential for facing the coronavirus disease ۲۰۱۹ (COVID-۱۹) pandemic. Depending on competitive enzyme-linked immunosorbent assay (ELISA) methodology, the current study assay was designed to simulate the virus-host interaction using purified SARS-COV-۲-RBD from the spike protein and the host cell receptor human angiotensin-converting enzyme ۲ protein. The performance of this in-house neutralizing ELISA assay was validated using freshly prepared standards with different known concentrations of the assay. In this regard, a cohort of ۵۰ serum samples from convalescent COVID-۱۹ individuals with different disease severity at different time points post-recovery and a cohort of ۵۰ serum samples from healthy individuals were processed by the in-house developed assay for detecting SARS-CoV-۲ nAbs, in comparison with a commercial total anti-SARS-CoV-۲ IgG antibody assay as a gold standard. The assay obtained a sensitivity of ۸۸% (۹۵% CI: ۷۵.۶۹-۹۵.۴۷) and a specificity of ۹۲% (۹۵% CI: ۸۰.۷۷- ۹۷.۷۸%). A negative strong correlation was demonstrated in the standard curve between the optical density absorbance and log concentration of the nAbs with a statistical measure of r۲ (coefficient of determination) = ۰.۹۵۳۹. The SARS-COV-۲-RBD neutralizing ELISA assay serves as a high throughput qualitative and quantitative tool that can be applied in most laboratory settings without special biosafety requirements to detect anti-RBD nAbs for seroprevalence, pre-clinical, and clinical evaluation of COVID-۱۹ vaccines efficiency and the rapid selection of convalescent plasma donors for the treatment of COVID-۱۹ patients.

covid-۱۹, nAbs, neutralizing antibodies, SARS-COV-۲-RBD neutralizing ELISA assay