Population impact of Vi capsular polysaccharide vaccine.

Development of a safe and efficacious vaccine against typhoid fever has been the mainstay of enteric vaccinology since production of the first parenteral whole-cell typhoid vaccine in 1896. The new-generation Vi polysaccharide single-dose injectable typhoid vaccine developed in the 1980s is widely used in countries where it is locally produced, such as China, and in travelers from industrialized countries to typhoid-endemic settings. However, Vi vaccine use is limited to private practice at a small scale by residents of high-burden countries such as India, Pakistan and Bangladesh. Recognition of the public health importance of typhoid fever prevention has significantly increased due to the emergence of antimicrobial-resistant strains of Salmonella enterica serovar Typhi in recent years. Recent evidence of herd protection conferred by the Vi vaccine has highlighted the significance of the vaccine's effects beyond the vaccinated population. The large-scale use of this vaccine can yield protective benefits to a larger population and can reduce the epidemiologic and economic burden of typhoid fever in endemic countries.