Safety and Immunogenicity of a Vi-DT Typhoid Conjugate Vaccine

This study will be carried out in healthy adults and children at a single site. Subjects will be stratified according to age. The study procedure is as follows: Visit 1 (day-1 to -7): Screen participants by medical history, physical examination and lab investigations. Collect blood for safety and immunogenicity assessments. Visit 2 (day 0): Enroll, randomize and administer first dose of vaccine to eligible participants Visit 3 (day 3): Assess participant safety by medical history and physical examination Visit 4 (day 7): Record solicited adverse reaction 7 days post vaccination, and collect blood for safety lab assessments. Visit 5 (day 28): Assess participant safety, collect blood for immunogenicity assessments, and administer second vaccine dose Visit 6 (day 31): Participants safety will be assessed by medical history and physical examination Visit 7 (day 35): Record solicited adverse reaction 7 days post second vaccination. Visit 8 (day 56): Collect blood for immunogenicity assessments, assess participant safety, and fill in study completion form in the absence of any safety concern. This study is observer-blind: vaccine administrator and vaccine safety evaluator will be two distinct persons to avoid bias of safety assessment. Trial staff other than the vaccine administrator.