Safety and immunogenicity of two different lots of the oral, killed enterotoxigenic Escherichia coli cholera toxin B subunit vaccine in Israeli youngadults

Enterotoxigenic Escherichia coil (ETEC) is one of the leading causes of dia rrhea among Israeli soldiers serving in field units. Two double-blind place bo-controlled, randomized trials were performed among 155 healthy volunteer s to evaluate the safety and immunogenicity of different lots of the oral, killed ETEC vaccine consisting of two doses of whole cells plus recombinant ly produced cholera toxin B subunit (rCTB). The two doses of vaccine lot E0 05 and the first dose of vaccine lot E003 were well tolerated by the volunt eers. However, 5 (17%) vaccinees reported an episode of vomiting a few hour s after the second dose of lot E003; none of the placebo recipients reporte d similar symptoms. Both lots of vaccine stimulated a rate of significant a ntibody-secreting cell (ASC) response to CTB and to colonization factor ant igen I (CFA/I) after one or two doses, ranging from 85 to 100% and from 81 to 100%, respectively. The rate of ASC response to CS2, CS4, and CS5 was sl ightly lower than the rate of ASC response induced to CTB, CFA/I, and CS1. The second vaccine dose enhanced the response to CTB but did not increase t he frequencies or magnitude of ASC responses to the other antigens. The two lots of the ETEC vaccine induced similar rates of serum antibody responses to CTB and CFA/I which were less frequent than the ASC responses to the sa me antigens. Based on these safety and immunogenicity data, an efficacy stu dy of the ETEC vaccine is under way in the Israel Defense Force.