application and validation of sars-cov-2 rbd neutralizing elisa assay

The establishment of an approach for detecting the anti-severe acute respiratory syndrome coronavirus-2 (sars-cov-2)-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 2019 (covid-19) 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-2-rbd from the spike protein and the host cell receptor human angiotensin-converting enzyme 2 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 50 serum samples from convalescent covid-19 individuals with different disease severity at different time points post-recovery and a cohort of 50 serum samples from healthy individuals were processed by the in-house developed assay for detecting sars-cov-2 nabs, in comparison with a commercial total anti-sars-cov-2 igg antibody assay as a gold standard. the assay obtained a sensitivity of 88% (95% ci: 75.69-95.47) and a specificity of 92% (95% ci: 80.77- 97.78%). 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 r² (coefficient of determination) = 0.9539. the sars-cov-2-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-19 vaccines efficiency and the rapid selection of convalescent plasma donors for the treatment of covid-19 patients.