2.5 Neutralization assay
The pseudo-neutralization assay was performed by using the SARS-CoV2
Neutralization Antibody Elisa Kit (Invitrogen) as per manufacturers
protocol. In brief, plasma samples were diluted 1:50 and added to wells
coated with SARS-CoV2 RBD (Receptor Binding Domain) antigen followed by
incubation and addition of Biotin conjugate. After required incubation
period Streptavidin-HRP conjugate was added followed by addition of
Substrate solution (TMB) and Stop solution after successive incubation
periods. The plate was read on iMark microplate absorbance reader
(Bio-Rad) using 450nm wavelength. Neutralization % was calculated by
the following formula:
Neutralization (%) = 1- (Absorbance of unknown sample/Absorbance of
negative control) × 100
> 20% = Positive
< 20% = Negative