Effectiveness of Vi capsular polysaccharide typhoid vaccine among children: A cluster randomized trial in Karachi, Pakistan

► We present effectiveness of Vi typhoid vaccine in children in Pakistan. ► Cluster randomized trial design was used to evaluate the vaccine effectiveness. ► Vi typhoid vaccine did not protect young children aged between 2 and 5 years. ► Immune response to Vi typhoid vaccine waned rapidly in younger children. ► Protection in children 5-15 years of age was similar to previous studies.