Typhoid Vi: a less reactogenic vaccine.

A typhoid vaccine derived from the purified Vi capsular polysaccharide (CPS) antigen of Salmonella typhi was compared with a heat-killed whole-cell typhoid vaccine in 637 healthy male volunteers. The individuals were placed in three groups: group 1 received two doses of heat-killed whole-cell typhoid vaccine, at an interval of 28 days; group 2 received a single dose of typhoid Vi CPS vaccine followed after 28 days by water for injection; and group 3 received water for injection on the first occasion and a single dose of typhoid Vi CPS vaccine 28 days later. Local and systemic adverse reactions were recorded for 5 days following each injection. Subjects receiving the typhoid Vi CPS vaccine complained of fewer local adverse reactions on each of the first 3 days following immunization: on day 1, 18.6% of subjects given typhoid Vi CPS vaccine reported local reactions compared with 59.7% of those receiving heat-killed whole-cell vaccine (P less than 0.001). The percentage of subjects receiving the heat-killed whole-cell vaccine who complained of systemic reactions was more than twice that of subjects receiving the Vi CPS vaccine (7.9% and 3.4%, respectively, on day 1; P less than 0.01).