This study is part of International Vaccine Institutes (IVI)'s typhoid Vi demonstration project that aims to accelerate the rational introduction of Vi vaccines in typhoid endemic countries. The primary objectives of the study are to evaluate the logistic feasibility of a mass typhoid fever immunization campaign program targeting school age children in Hue City, Vietnam and to assess the knowledge, attitudes, beliefs, and practices of parents and healthcare providers in Hue City regarding typhoid fever prevention and treatment.

Typhoid fever is a major cause of morbidity worldwide. The disease predominantly affects school-aged children, is more prevalent in urban areas, may last for several weeks and can lead to serious complications. Management of this disease is further complicated by the emergence of multi-drug resistant strains. Vaccination of high risk populations is considered the most promising strategy for the control of typhoid fever. The Vi polysaccharide vaccine has been targeted for accelerated introduction into public health programs due to the following reasons: it has been shown to have consistent efficacy results even in areas of high typhoid incidence, is given as a single dose, lacks patent protection and requires less strict cold chain requirements. A cluster-randomized trial involving the Vi polysaccharide vaccine and an active control (Hepatitis A) was designed to determine the logistic feasibility of providing Vi vaccine under actual programmatic conditions among school students in Hue City. The vaccines used in this study are internationally produced and locally licensed.

Secondary objectives of this trial are:

• To estimate the cost-effectiveness (cost of illness, willingness to pay, vaccine delivery costs, private vaccine costs, etc) of Vi vaccination
• To determine the effectiveness of the Vi polysaccharide vaccine following routine administration of a 1-dose schedule to school students (aged >=6 years)
• To determine the safety and immunogenicity of the Vi vaccine
• To study typhoid risk factors among students

A nested, prospective matched case-control study is included in the trial in order to study typhoid risk factors among children in Hue City.

Inclusion Criteria:

• Local students whose parents/guardians provide written consent to receive Vi vaccine
• Attending any of the 66 registered schools in Hue
• Registered in the project census
• Lives in Hue City

Exclusion Criteria:

• Fever (>37.5 degrees Celsius, axillary)
• Pregnancy
• Lactating