title: Comparison of the immunogenicity and safety of two different brands of Salmonella typhi Vi capsular polysaccharide vaccine.
abstract: BACKGROUND
  The recent emergence of multi-drug-resistant Salmonella strains highlights the need for better preventive measures, including vaccination. Safe and immunologic vaccines have been developed based on purified Vi polysaccharide.
  
  
  OBJECTIVE
  To compare the immune response elicited by two different brands of Salmonella Vi capsular polysaccharide vaccine (ViCPS).
  
  
  METHODS
  Double blind, randomized (3:1), controlled, parallel, phase III study was conducted at two centres in India to compare the safety and immunogenicity of Typbar, the investigational vaccine with an already marketed vaccine "X", in healthy subjects aged between 12 -25 years.
  
  
  METHODS
  A sample size of 184 subjects was calculated. Subjects were randomly distributed in two groups, immunized with single dose of Typbar or Vaccine "X". Serum samples were taken before 7 days and 4 weeks after immunization for the determination of antibodies to Vi polysaccharide, by ELISA method. Safety was assessed by physical examination, laboratory parameters before and after vaccination and by monitoring adverse events.
  
  
  METHODS
  The geometric mean antibody titre (GMT) 4 weeks after vaccination was compared from respective pre-vaccination values by Wilcoxon signed rank test. Geometric mean of antibody levels before and after immunization and the ratio between them (Mann-Whitney test), the Seroconversion rates (Z test of proportions) and the adverse events (Fisher's exact test and Chi square test), were compared between two groups. P value < 0.05 was considered statistically significant. P values and 95% confidence intervals were estimated in two-tailed fashion.
  
  
  RESULTS
  153 subjects (Typbar =116 and Vaccine "X" =37) were studied. 71.6% (95% CI=63.4%-79.8%) and 75.7% (95% CI=64.9% - 89.5%) were the seroconversion rates with Typbar and vaccine "X" respectively. The GMT values for Vi antibodies induced after Typbar and vaccine "X" were 10.23 Typbar and 13.46 mg/mL respectively and these values showed high significance when compared to their respective pre-immunization GMT values (P<0.0001) at 95% CI (-10.49 to -7.19 mg/mL for Typbar and -14.69 to -8.86 mg/mL for Vaccine "X"). The induction of antibody response appeared to be slightly stronger (P=0.032) with vaccine "X" when compared to that of Typbar. This is justifiable as the same group also had high pre-immunization GMT values (P=0.021).
  
  
  CONCLUSIONS
  The immunogenicity and safety of the investigational vaccine Typbar was found to be similar to that of already marketed brand of Vi CPS, Vaccine "X". The availability of a single dose of vaccine that is safe and effective enhances the prospective for control of typhoid fever.
authors.affiliation: Department of Pharmacology, Kasturba Medical College, P.B. no. 53, Mangalore-575001, India. sabita_rao1@rediffmail.com
authors.forename: P
authors.initials: P
authors.lastname: Sabitha
authors.forename: M R
authors.initials: MR
authors.lastname: Prabha Adhikari
authors.forename: Abhijit
authors.initials: A
authors.lastname: Chowdary
authors.forename: Malathi
authors.initials: M
authors.lastname: Prabhu
authors.forename: Mohammad
authors.initials: M
authors.lastname: Soofi
authors.forename: Meenakshi
authors.initials: M
authors.lastname: Shetty
authors.forename: Asha
authors.initials: A
authors.lastname: Kamath
authors.forename: S S
authors.initials: SS
authors.lastname: Lokaranjan
authors.forename: S S
authors.initials: SS
authors.lastname: Bangera
mesh_terms: D000293:Adolescent; D000328:Adult; D000907:Antibodies, Bacterial / Q000097:blood*; D002648:Child; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D011135:Polysaccharides, Bacterial / Q000009:adverse effects / Q000276:immunology*; D022562:Salmonella Vaccines / Q000009:adverse effects / Q000276:immunology*; D012485:Salmonella typhi / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D011135:Polysaccharides, Bacterial; D022562:Salmonella Vaccines; C054154:capsular polysaccharide, Salmonella