Enteric fevers, of which typhoid fever is the most common, remain a serious and frequent cause of morbidity and mortality in most underdeveloped nations. These group of diseases are caused by the Genus salmonellae. The most frequent and serious of these enteric fevers in underdeveloped nations is typhoid fever caused by the Salmonella typhi. The next most common cause of enteric fevers in underdeveloped nations is Salmonella paratyphi A. Evaluation of vaccines for prevention of these diseases has a long and variegated history because both organisms are inhabitants of pathogens for humans only. Two, double-masked, randomized, controlled evaluations of the Vi of Salmonella typhi has shown its ability to prevent typhoid fever in Nepal and in the Eastern Transvaal of the Republic of South Africa. No significance side reactions were observed and effectiveness rate of 70% has been observed for two years. Surveillance and long-term serologic studies are in progress. Based upon these data, new vaccines for the prevention of non-typhoidal enteric fevers using the Vi capsular polysaccharide O-specific side chain of Salmonella paratyphi A covalently bound to carrier proteins is in progress.
