Typhoid Fever Immunization

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 clusterrandomized 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. in reported cases of typhoid fever, from 4,859 cases in 1990 to 30,901 in 1995 (Trach, 1998; Ministry of Health, 1996). The estimated national disease incidence is approximately 33.4 per 100,000 per year (1991-2003). Additionally, major outbreaks involving schoolchildren have occurred in southern and central Vietnam. The control of enteric infections requires the provision of safe drinking water and human waste removal systems, and the identification and treatment of carriers. The increasing number of Salmonella enterica subspecies enterica serovar typhi (S. typhi) strains that are resistant to multiple antibiotics is a growing threat. More than 80% of S. typhi strains in the Mekong Delta are now resistant to ampicillin, chloramphenicol, SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH 516 Vol 37 No. 3 May 2006 nalidixic acid or ciprofloxacin (Parry et al, 1998; Wain and Kidgell, 2004). Because the cost of these control measures may be beyond a developing country’s health budget, typhoid fever immunization would be a realistic public health option (WHO, 2000). The World Health Organization (WHO) recommends routine immunization of school-aged children as part of the activities to reduce typhoid fever (WHO, 2003). However, immunization as a method to prevent typhoid fever is not widely used. A few countries, such as China and Vietnam, are leading the way in the use of these vaccines as a public health tool. The Vietnamese Institute of Vaccine and Biological Substances (IVAC) has been responsible for the vaccine production for the local Expanded Program on Immunization (EPI) since 1982, and recently for other vaccines. In 1999, IVAC produced the first batch of Vi polysaccharide (Vi PS) vaccine (Robbins and Robbins, 1984). A bridging trial demonstrated that this locally produced vaccine was as safe and immunogenic as licensed Vi PS vaccines produced in developed countries (Ke NT et al, unpublished observations). It is anticipated that production of Vi PS will be scaled up by 2007, with a production capacity of 6-10 million doses per year. Thus, Vietnam will be self-sufficient in providing vaccines for high-risk populations such as schoolchildren nationwide. With the expanded availability of an affordable Vi PS vaccine, policyrelevant data are needed to streamline the typhoid fever vaccination strategy. We report on the coverage, safety, and logistics of a school-based Vi PS immunization campaign in Hue City, Vietnam that was conducted in late 2003. This project, which is part of a multi-country multidisciplinary evaluation (Acosta et al, 2004), aims to contribute to the design and fine-tuning of a national typhoid fever immunization strategy that will in turn accelerate the introduction of the Vi PS vaccine in Vietnam.