Field Trial of Attenuated Salmonella typhi Live Oral Vaccine Ty21a in Liquid and Enteric-Coated Formulations and Epidemiological Survey for Incidence of Diarrhea Due to Shigella Species

By studying the epidemiology and prevention of enteric infections in cohorts of children in a less-developed area, one can gain insights that are, directly applicable to the prevention of enteric infections in adult military travelers. Santiago, Chile was deemed a particularly attractive site to carry out studies of the epidemiology of enteric infections because a wide array of diarrheal pathogens were known to be prevalent. There also exists in Santiago an excellent health care infrastructure, as well as motivated and well-trained microbiologists and epidemiologists. The enteric diseases field project in Santiago, Chile had four broad objectives 1 to directly compare in a large- scale, randomized, placebo-controlled field trial, the efficacy of live oral typhoid vaccine, Ty2la, when administered in a liquid suspension or in enteric- coated capsules 2 to intensively RA 1 Typhoid Vaccine Diarrhea Shigella study the epidemiology of endemic Shigella infections in children residing in a low socioeconomic level community in Santiago 3 to develop, modify, standardize, and transfer to Chile practical DNA probe methods that would allow the processing of large numbers of clinical specimens to detect the various categories of E. coli associated with diarrheal disease and 4 to study the epidemiology of diarrheal disease due to the various categories of diarrheagenic E. coli. Results of three years of surveillance of the direct comparison of formulations of Ty2la unequivocally demonstrate that the liquid formulation is significantly superior.Over three years of surveillance, this formulation conferred 77 protection against confirmed typhoid fever.