Fig. 3.

Specificity of S. typhi Vi ELISA to detect IgG in sera from vaccinated individuals by direct inhibition.The mean absorbance (A_{405 nm}) and inhibition (%) of IgG anti-S. typhi Vi in sera (one in 50 dilution) from two vaccinated subjects A and B was assessed following an overnight preadsorption with or without varying concentrations of S. typhi Vi antigen. Following preadsorption, sera A and B were used in the ELISA immediately. Sera A and B contained 45 AU/ml and 23 AU/ml anti-S. typhi Vi IgG, respectively. Results from a representative experiment are shown.