title: A cluster-randomized effectiveness trial of Vi typhoid vaccine in India.
abstract: BACKGROUND
  Typhoid fever remains an important cause of illness and death in the developing world. Uncertainties about the protective effect of Vi polysaccharide vaccine in children under the age of 5 years and about the vaccine's effect under programmatic conditions have inhibited its use in developing countries.
  
  
  METHODS
  We conducted a phase 4 effectiveness trial in which slum-dwelling residents of Kolkata, India, who were 2 years of age or older were randomly assigned to receive a single dose of either Vi vaccine or inactivated hepatitis A vaccine, according to geographic clusters, with 40 clusters in each study group. The subjects were then followed for 2 years.
  
  
  RESULTS
  A total of 37,673 subjects received a dose of a study vaccine. The mean rate of vaccine coverage was 61% for the Vi vaccine clusters and 60% for the hepatitis A vaccine clusters. Typhoid fever was diagnosed in 96 subjects in the hepatitis A vaccine group, as compared with 34 in the Vi vaccine group, with no subject having more than one episode. The level of protective effectiveness for the Vi vaccine was 61% (95% confidence interval [CI], 41 to 75; P<0.001 for the comparison with the hepatitis A vaccine group). Children who were vaccinated between the ages of 2 and 5 years had a level of protection of 80% (95% CI, 53 to 91). Among unvaccinated members of the Vi vaccine clusters, the level of protection was 44% (95% CI, 2 to 69). The overall level of protection among all residents of Vi vaccine clusters was 57% (95% CI, 37 to 71). No serious adverse events that were attributed to either vaccine were observed during the month after vaccination.
  
  
  CONCLUSIONS
  The Vi vaccine was effective in young children and protected unvaccinated neighbors of Vi vaccinees. The potential for combined direct and indirect protection by Vi vaccine should be considered in future deliberations about introducing this vaccine in areas where typhoid fever is endemic. (ClinicalTrials.gov number, NCT00125008.)
authors.affiliation: National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: Dipika
authors.initials: D
authors.lastname: Sur
authors.forename: R Leon
authors.initials: RL
authors.lastname: Ochiai
authors.forename: Sujit K
authors.initials: SK
authors.lastname: Bhattacharya
authors.forename: Nirmal K
authors.initials: NK
authors.lastname: Ganguly
authors.forename: Mohammad
authors.initials: M
authors.lastname: Ali
authors.forename: Byomkesh
authors.initials: B
authors.lastname: Manna
authors.forename: Shanta
authors.initials: S
authors.lastname: Dutta
authors.forename: Allan
authors.initials: A
authors.lastname: Donner
authors.forename: Suman
authors.initials: S
authors.lastname: Kanungo
authors.forename: Jin Kyung
authors.initials: JK
authors.lastname: Park
authors.forename: Mahesh K
authors.initials: MK
authors.lastname: Puri
authors.forename: Deok Ryun
authors.initials: DR
authors.lastname: Kim
authors.forename: Dharitri
authors.initials: D
authors.lastname: Dutta
authors.forename: Barnali
authors.initials: B
authors.lastname: Bhaduri
authors.forename: Camilo J
authors.initials: CJ
authors.lastname: Acosta
authors.forename: John D
authors.initials: JD
authors.lastname: Clemens
mesh_terms: D000293:Adolescent; D000328:Adult; D000907:Antibodies, Bacterial / Q000097:blood; D002648:Child; D002675:Child, Preschool; D003906:Developing Countries; D022362:Hepatitis A Vaccines / Q000009:adverse effects; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007194:India; D010284:Paratyphoid Fever / Q000453:epidemiology; D011135:Polysaccharides, Bacterial / Q000009:adverse effects / Q000276:immunology*; D011159:Population Surveillance; D012485:Salmonella typhi / Q000276:immunology; D016896:Treatment Outcome; D014435:Typhoid Fever / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control*; D014436:Typhoid-Paratyphoid Vaccines / Q000009:adverse effects / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D022362:Hepatitis A Vaccines; D007074:Immunoglobulin G; D011135:Polysaccharides, Bacterial; D014436:Typhoid-Paratyphoid Vaccines; C057664:Vi polysaccharide vaccine, typhoid