Antibody responses to heat-killed, phenol preserved parenteral typhoid vaccine.

The heat-killed, phenolized parenteral typhoid vaccine was tested in informed volunteers. Assessment for its immunogenicity was performed using Widal test and enzyme-linked immunosorbent assay (ELISA). The anti-H antibody, which is a marker of the vaccine antigenicity peaked at one month after the vaccination and appeared throughout the one year course of the study. The anti-O antibody peaked at 7th day after vaccination and lasted only for 6 months. Classes of specific antibodies were determined by ELISA using single extracted lipopolysaccharide from Salmonella typhi 0901 as antigen. The possible protective role of serum derived intestinal IgG and IgA were discussed. Based on the agglutinating antibodies, the results indicate that the heat-killed, phenolized typhoid vaccine conferred at least 6 months protective period.