Community Participation in Two Vaccination Trials in Slums of Kolkata, India: A Multi-level Analysis.

This study aims at understanding the individual and community-level characteristics that influenced participation in two consecutive vaccine trials (typhoid and cholera) in urban slums of Kolkata, India. The study area was divided into 80 geographic clusters (communities), with 59,533 subjects aged ≥2 years for analysis. A multi-level model was employed in which the individuals were seen nested within the cluster. Rates of participation in both the trials were nearly the same; those who participated in the initial trial were likely to participate in the subsequent cholera vaccine trial. Communities with predominantly Hindu population, lower percentage of households with an educated household head, or lower percentage of households owning a motorbike had higher participation than their counterparts. At individual scale, higher participation was observed among younger subjects, females, and individuals from households with a household head who had no or minimal education. Geographic patterns were also observed in participation in the trials. The results illustrated that participation in the trial was mostly influenced by various individual and community-level factors, which need to be addressed for a successful vaccination campaign.

Adults' perceived prevalence of enteric fever predicts laboratory-validated incidence of typhoid fever in children.

This study was undertaken to develop a model to predict the incidence of typhoid in children based on adults' perception of prevalence of enteric fever in the wider community. Typhoid cases among children, aged 5-15 years, from epidemic regions in five Asian countries were confirmed with a positive Salmonella Typhi culture of the blood sample. Estimates of the prevalence of enteric fever were obtained from random samples of adults in the same study sites. Regression models were used for establishing the prediction equation. The percentages of enteric fever reported by adults and cases of typhoid incidence per 100,000, detected through blood culture were 4.7 and 24.18 for Viet Nam, 3.8 and 29.20 for China, 26.3 and 180.33 for Indonesia, 66.0 and 454.15 for India, and 52.7 and 407.18 for Pakistan respectively. An established prediction equation was: incidence of typhoid (1/100,000= -2.6946 + 7.2296 x reported prevalence of enteric fever (%) (F=31.7, p<0.01; R2=0.992). Using adults' perception of prevalence of disease as the basis for estimating its incidence in children provides a cost-effective behavioural epidemiologic method to facilitate prevention and control of the disease.

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.

The role of epidemiology in the introduction of vi polysaccharide typhoid fever vaccines in Asia.

Despite the availability of at least two licensed typhoid fever vaccines--injectable sub-unit Vi polysaccharide vaccine and live, oral Ty21a vaccine--for the last decade, these vaccines have not been widely introduced in public-health programmes in countries endemic for typhoid fever. The goal of the multidisciplinary DOMI (Diseases of the Most Impoverished) typhoid fever programme is to generate policy-relevant data to support public decision-making regarding the introduction of Vi polysaccharide typhoid fever immunization programmes in China, Viet Nam, Pakistan, India, Bangladesh, and Indonesia. Through epidemiological studies, the DOMI Programme is generating these data and is offering a model for the accelerated, rational introduction of new vaccines into health programmes in low-income countries. Practical and specific examples of the role of epidemiology are described in this paper. These examples cover: (a) selection of available typhoid fever vaccines to be introduced in the programme, (b) generation of policy-relevant data, (c) providing the 'backbone' for the implementation of other multidisciplinary projects, and (d) generation of unexpected but useful information relevant for the introduction of vaccines. Epidemiological studies contribute to all stages of development of vaccine evaluation and introduction.