The feasibility of a school-based VI polysaccharide vaccine mass immunization campaign in Hue City, central Vietnam: streamlining a typhoid fever preventive strategy.

We report the coverage, safety, and logistics of a school-based typhoid fever immunization campaign that took place in Hue City, central Vietnam; a typhoid fever endemic area. A cluster-randomized evaluation-blinded controlled trial was designed where 68 schools (cluster) were randomly allocated the single dose Vi polysaccharide vaccine (Typherix) or the active control hepatitis A vaccine (Havrix). A safety surveillance system was implemented. A total of 32,267 children were immunized with a coverage of 57.5%. Strong predictors for vaccination were attending primary schools, peri-urban location of the school, and low family income. Human resources were mainly schoolteachers and the campaign was completed in about 1 month. Most adverse events reported were mild. Safe injection and safe sharp-waste disposal practices were followed. A typhoid fever school-based immunization campaign was safe and logistically possible. Coverage was moderate and can be interpreted as the minimum that could have been achievable because individual written informed consent procedures were sought for the first time in Hue City and the trial nature of the campaign. The lessons learned, together with cost-effectiveness results to be obtained by the end of follow-up period, will hopefully accelerate the introduction of Vi typhoid fever vaccine in Vietnam.

Comparison of the immunogenicity and safety of two different brands of Salmonella typhi Vi capsular polysaccharide vaccine.

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). SETTING AND DESIGN: 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. MATERIAL AND 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. Statistics: 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). CONCLUSION: 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.

Safety and immunogenicity of a Haemophilus influenzae type B polysaccharide-tetanus toxoid conjugate vaccine combined with diphtheria, tetanus and pertussis vaccines in Thai infants.

A randomized, open, multicenter trial was conducted to determine the safety and immunogenicity of a Haemophilus influenzae type b polysaccharide-tetanus toxoid (PRP-T) conjugate vaccine combined with tetanus, diphtheria and pertussis (DTP) vaccine in 271 Thai infants born to mothers immunized against tetanus during pregnancy. Infants were immunized at approximately 2, 4 and 6 months of age with these vaccines. To determine if elevated levels of anti-tetanus toxin antibodies suppressed the anti-PRP antibody response, a second group of infants were immunized with PRP complexed with outer membrane proteins of Neisseria meningitidis (Pedvax HIB) in one limb at 2 and 4 months of age and DTP vaccine in the other limb at 2, 4 and 6 months of age. A third group of infants received only DTP vaccine at 2, 4 and 6 months of age. The occurrence of both local and systemic adverse reactions were comparable in all 3 groups. The geometric mean anti-tetanus antibody titer was > 1 IU/ml at baseline. Approximately 1 month after the administration of the third dose of vaccine, 98.5%, 99.3% and 9.7% of the children immunized with DTP+Pedvax HIB, DTP-PRP-T or DTP possessed > or = 0.15 microgram of anti-PRP antibody per ml. No child in the DTP group achieved > or = 1 microgram/ml while 74.2% and 89.3% did so after immunization with DTP+Pedvax HIB, or DTP-PRP-T, respectively (p < 0.05). Immune responses to diphtheria, tetanus and pertussis antigens were similar in all vaccine groups. These results demonstrate that elevated tetanus antibody titers do not diminish the anti-PRP antibody response following immunization with a PRP-T conjugate combined with DTP vaccine.