Controlled field trial with dried sorbed paratyphoid B and typhoid vaccines.

Abstract In 1968-70 a field trial was arranged in the USSR to evaluate the effectiveness of dried sorbed paratyphoid B and typhoid vaccines when administered in two doses separated by an interval of 20-30 days. Two groups of schoolchildren were under observation: a group inoculated with paratyphoid B vaccine (75 805 children) and a group inoculated with typhoid vaccine (76 314 children). The persons who were inoculated with the paratyphoid B vaccine formed the control group used in evaluating the effectiveness of the typhoid vaccine, and those inoculated with the typhoid vaccine formed the control group for the evaluation of the paratyphoid vaccine. Two doses of dried sorbed paratyphoid B vaccine made from Salmonella paratyphi B, strain No. 42, containing 5 × 108 microbial cells per injection, protected about 70% of those inoculated. Two doses of dried sorbed typhoid vaccine made from S. typhi, strain Ty 2 4446, also with 5 × 108 cells per injection, protected about 80% of those inoculated. At least 21 months of protection (the period of observation) were obtained following immunization with dried sorbed preparations made from heat-killed aerated broth cultures. Both types of vaccine produced the same frequency and intensity of general and local reactions; these were moderate. The general and local reactions to a second injection were substantially less marked than those to the first.