title: Vaccines for preventing typhoid fever.
abstract: BACKGROUND
  Whole cell vaccines, consisting of relatively crude preparations of Salmonella typhi administered parenterally, are effective but have a high incidence of adverse effects. Two vaccines have been developed more recently. Ty21a (an attenuated strain of S. typhi administered orally) and Vi (the purified bacterial capsule, given parenterally), have appeared less toxic than the older whole cell vaccines and are thought to be equally effective.
  
  
  OBJECTIVE
  The objective of this review was to assess the effects of typhoid fever vaccines.
  
  
  METHODS
  We searched the Cochrane Library, Medline, Index Medicus, Embase and reference lists of articles.
  
  
  METHODS
  Randomised trials comparing typhoid vaccines to other types of vaccine or placebo.
  
  
  METHODS
  Two reviewers independently assessed trial quality and extracted data.
  
  
  RESULTS
  Seventeen studies, involving nearly two million people, were included. For the whole cell vaccines single dose regimens provided significant protection for the first two years. Two dose regimens provided significant protection for five years. For the Ty21a vaccine, both two and three dose regimens provided statistically significant protection for two years. The three dose regimen provided protection in the third and fourth years, but protection was not statistically significant in the fifth year. The Vi vaccine provided protection for two years, but the protection in the third year was not significant. The three year cumulative efficacy of two doses of whole cell vaccines was 73% (95% confidence interval 65-80), three doses of Ty21a was 51%, (95% confidence interval 35 to 63) and one dose of Vi was 55% (95% confidence interval 30 to 71). Data on adverse effects were limited, but indicate that whole cell vaccines are more toxic than the newer Ty21a and Vi vaccines.
  
  
  CONCLUSIONS
  The whole cell vaccines provided more prolonged protection than either the Ty21a vaccine or the Vi vaccine. However whole cell vaccines are associated with higher toxicity.
authors.affiliation: Viral Epidemiology Branch, National Cancer Institute, 6130 Executive Blvd, EPN 434, Rockville, MD, USA. engelse@exchange.nih.gov
authors.forename: E A
authors.initials: EA
authors.lastname: Engels
authors.forename: J
authors.initials: J
authors.lastname: Lau
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D006801:Humans; D012485:Salmonella typhi / Q000276:immunology; D014435:Typhoid Fever / Q000276:immunology / Q000517:prevention & control*; D014436:Typhoid-Paratyphoid Vaccines / Q000008:administration & dosage / Q000627:therapeutic use*; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000627:therapeutic use
chemical_list: D014436:Typhoid-Paratyphoid Vaccines; D014613:Vaccines, Attenuated