This project is for an efficacy trial (Phase 3) Of Vi-rEPA (Vi-recombinant exoprotein A of Pseudomonas aeroginosa) and S para A-TT (Salmonella paratyphi A-tetanus toxoid) investigational vaccines developed by the NICHD, NIH, Vi and S. paratyphi A conjugates will be evaluated for enteric fevers in the Dong Thap Province of Vietnam in a randomized double blinded, vaccine-controlled trial in about 16,000 children, ages 2 to 5 years.
Children will be randomized to receive 2 injections, spaced 6 weeks apart, of either Vi or S. paratyphi A conjugates. The study area will include 16 communes/Town of Cao Lanh District, Done Thap Province (population of 2-5 years old about 17,000). A baseline epidemiological study showed a high incidence of typhoid fever in the study population with an incidence of blood culture confirmed typhoid fever at 0.43/100/year in 2-4 years old children. Census will be conducted before recruitment of subjects. Each injection of vaccine will be completed its about 2-3 weeks. An intensive lever surveillance and blood culture of fever cases will be carried out by all health facilities of the study communes as well as the Provincial Hospital for at least 24 months following vaccination to identify enteric fever caused by S. typhi or S. paratyphi A. This will be followed by a less intensive passive blood culture surveillance for an additional year. A subset of randomly selected children (one child each week at each commune during the entire study period) will be asked to give blood for the study of persistence of vaccine-induced antibody. Laboratory investigation and data management will be carried out at the Dong Thap Provincial Hospital. The end point for vaccine efficacy will be blood culture confirmed enteric fever.