title: Immunogenicity, efficacy and serological correlate of protection of Salmonella typhi Vi capsular polysaccharide vaccine three years after immunization.
abstract: The protective efficacy and immunogenicity of Vi capsular polysaccharide vaccine against typhoid fever was measured 3 years after its administration in a double-blind randomized trial. Vaccine efficacy was not significantly different during each year of the trial and was 55% (95% CI: 30-71%) over the 3 year period. In a case-control study at 3 years after vaccination, recipients of Vi had higher levels of Vi antibodies than controls, as measured by radio-immunoassay (GMT 1.28 vs 0.76 microgram ml-1, P = 0.0004) and by passive haemagglutination assay (GMT 10.46 vs 3.52, P = 0.0001). The serological correlate of protection has been estimated using the relative risks of typhoid fever in the 2 groups and the relative ratio of antibody levels. The estimated protective level is 1 microgram ml-1 suggesting that at a mean age of 9 years, 64% of vaccinates and 40% of controls had protective antibody against typhoid fever in this endemic area.
authors: Department of Medical Microbiology, School of Pathology, SAIMR/University of the Witwatersrand, Johannesburg, South Africa.
authors: K P
authors: KP
authors: Klugman
authors: H J
authors: HJ
authors: Koornhof
authors: J B
authors: JB
authors: Robbins
authors: N N
authors: NN
authors: Le Cam
mesh_terms: D000293:Adolescent; D000907:Antibodies, Bacterial / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007114:Immunization; D008297:Male; D011135:Polysaccharides, Bacterial / Q000276:immunology*; D012485:Salmonella typhi / Q000276:immunology*; D013997:Time Factors; D014436:Typhoid-Paratyphoid Vaccines / Q000276:immunology*; D018074:Vaccines, Conjugate / Q000276:immunology
chemical_list: D000907:Antibodies, Bacterial; D011135:Polysaccharides, Bacterial; D014436:Typhoid-Paratyphoid Vaccines; D018074:Vaccines, Conjugate; C054154:capsular polysaccharide, Salmonella