title: Immune responses to Vi capsular polysaccharide typhoid vaccine in children 2 to 16 years old in Karachi, Pakistan, and Kolkata, India.
abstract: The geometric mean concentration (GMC) and the proportion maintaining a protective level (150 enzyme-linked immunosorbent assay (ELISA) units [ELU]/ml) 2 years following a single dose of 25 μg of injectable Vi capsular polysaccharide typhoid vaccine was measured against that of the control hepatitis A vaccine in children 2 to 16 years old in cluster randomized trials in Karachi and Kolkata. The GMC for the Vi group (1,428 ELU/ml) was statistically significantly different from the GMC of the control hepatitis A vaccine group (86 ELU/ml) after 6 weeks. A total of 117 children (95.1%) in the Vi group and 9 (7.5%) in the hepatitis A group showed a 4-fold rise in Vi IgG antibody concentrations at 6 weeks (P < 0.01). Protective antibody levels remained significantly different between the two groups at 2 years (38% in the Vi vaccine groups and 6% in the hepatitis A group [P < 0.01]). A very small proportion of younger children (2 to 5 years old) maintained protective Vi IgG antibody levels at 2 years, a result that was not statistically significantly different compared to that for the hepatitis A group (38.1% versus 10.5%). The GMCs of the Vi IgG antibody after 2 years were 133 ELU/ml for children 2 to <5 years old and 349 ELU/ml for children 5 to 16 years old. In conclusion, Vi capsular polysaccharide typhoid vaccine is immunogenic in children in settings of South Asia where typhoid is highly endemic. The antibody levels in children who received this vaccine remained higher than those in children who received the control vaccine but were significantly reduced at 2 years of follow-up.
authors.affiliation: International Vaccine Institute, Seoul, Republic of Korea.
authors.forename: R Leon
authors.initials: RL
authors.lastname: Ochiai
authors.forename: M Imran
authors.initials: MI
authors.lastname: Khan
authors.forename: Sajid B
authors.initials: SB
authors.lastname: Soofi
authors.forename: Dipika
authors.initials: D
authors.lastname: Sur
authors.forename: Suman
authors.initials: S
authors.lastname: Kanungo
authors.forename: Young A
authors.initials: YA
authors.lastname: You
authors.forename: M Atif
authors.initials: MA
authors.lastname: Habib
authors.forename: Shah Muhammad
authors.initials: SM
authors.lastname: Sahito
authors.forename: Byomkesh
authors.initials: B
authors.lastname: Manna
authors.forename: Shanta
authors.initials: S
authors.lastname: Dutta
authors.forename: Camilo J
authors.initials: CJ
authors.lastname: Acosta
authors.forename: Mohammad
authors.initials: M
authors.lastname: Ali
authors.forename: Sujit K
authors.initials: SK
authors.lastname: Bhattacharya
authors.forename: Zulfiqar A
authors.initials: ZA
authors.lastname: Bhutta
authors.forename: John D
authors.initials: JD
authors.lastname: Clemens
mesh_terms: D000293:Adolescent; D000907:Antibodies, Bacterial / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D022362:Hepatitis A Vaccines / Q000008:administration & dosage / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007194:India; D008297:Male; D010154:Pakistan; D011135:Polysaccharides, Bacterial / Q000276:immunology*; D014436:Typhoid-Paratyphoid Vaccines / Q000008:administration & dosage* / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D022362:Hepatitis A Vaccines; D007074:Immunoglobulin G; D011135:Polysaccharides, Bacterial; D014436:Typhoid-Paratyphoid Vaccines; C054154:capsular polysaccharide, Salmonella