CLINICAL AND SEROLOGICAL RESPONSES FOLLOWING PRIMARY AND BOOSTER IMMUNIZATION WITH SALMONELLA-TYPHI-VI CAPSULAR POLYSACCHARIDE VACCINES

Clinical and serum antibody responses following intramuscular injection of two formulations of Salmonella typhi Vi capsular polysaccharide (Vi) were assessed in a double-blind evaluation. Healthy adults were randomly assigned to receive a 25 mu g dose of liquid (Vi-Liq, n = 182) or freeze-dried Vi vaccine (Vi-Lyoph; n = 55), or placebo (n = 86). Erythema and/or induration greater than or equal to 1 cm in diameter at the injection site developed in 13/182 (7%) of Vi-Liq and 3/55 (5%) of Vi-Lyoph recipients (not significant, n.s.). Fever (oral temperature greater than or equal to 100 degrees F(37.8 degrees C)) occurred in <2% of vaccinees. The frequencies of rises of fourfold or greater and of maximal Vi antibody levels were similar in the two vaccine groups. Fourfold or greater rises in ser um Vi antibody levels (RIA) developed in 53% of Vi-Lyoph and 60% of Vi-Liq recipients by I week (n.s.), and 98 and 93%, respectively, by I month (n.s.). The frequencies of adverse reactions and mean Vi antibody levels following booster immunization with Vi-Liq 27 to 34 months after primary immunization (n = 55) were similar to those observed following primary immunization, although subjects given a booster dose were more likely to develop local reactions greater than or equal to 1 cm in diameter than those given a first dose (10/55 versus 13/182, p = 0.013 by the chi(2) test). Primary and booster immunizations with the Vi vaccines are well tolerated in healthy adults, mean Vi antibody levels remain significantly elevated for up to 34 months after primary immunization.