Availability of safe drinking water, proper food hygiene, and sanitary disposal of excreta are the most cost-effective strate-gies for reducing the incidence of typhoid fever in endemic countries. These measures not only reduce the incidence of typhoid fever but also reduce other enteric infections, which are a major cause of morbidity and mortality in those areas.
Immunization with typhoid vaccines at regular intervals also considerably reduces the incidence of typhoidal Salmonella infections. Routine typhoid vaccination is indicated for (i) persons with intimate exposure (e.g., household contact) to S. Typhi cases or carrier; (ii) travelers to countries associatedwith an increased risk of exposure to S. Typhi; and (iii) micro-biology laboratory personnel working with S. Typhi. The fol-lowing two types of typhoid vaccines, killed and oral, are used:
TAB vaccine: The TAB vaccine is a killed whole cell vaccinethat contains heat-killed and 0.5% phenol-preserved S. Typhi, 1000 million/mL, and S. Paratyphi A and B, 750 million each per mL. The vaccine has been used for many years in India and in other countries, endemic for enteric fever. The vaccine is given subcutaneously in two doses of 0.5 mL each at an interval of 4–6 weeks, followed by a booster dose every 3 years. Field trials have shown overall efficacy of 70–90% in typhoid fever for a period of 3–7 years. Fever and pain at the site of injection are the side effects. Injection of a large volume of antigen is also another concern. Therefore, in India, divalent typhoid– paratyphoid A vaccine without S. Paratyphi B is used instead of the trivalent TAB vaccine, because S. Paratyphi B infection is not that common in the country.
Vi capsular polysaccharide antigen vaccine (ViCPS): TheViCPS antigen vaccine is composed of purified Vi antigen, the capsular polysaccharide produced by S. Typhi isolated from blood cultures. Primary vaccination with ViCPS is carried out by a single parenteral dose of 0.5 mL (25 g IM). Booster doses are needed every 2 years to maintain protection, if continued or renewed exposure to S. Typhi is expected. Two field trials showed overall protection rates of 50–64% in South Africa and 72% in Nepal, the areas endemic for the disease. Fever, headache, erythema, and induration are some of the side effects. The vaccine is not recommended for children below 2 years.
Acetone-inactivated parenteral vaccine: This vaccine iscurrently available only in the United States only for military use. The vaccine has shown an efficacy of 75–94%. Booster doses are given every 3 years, if continued or renewed exposure is expected.