Typhim Vi

This is a parenteral vaccine containing purified Vi polysaccharide antigen extracted from the bacterial capsule of S.typhi strain Ty2.

• composed of purified Vi capsular polysaccharide from S. typhi. Each 0.5ml dose contains 25µg of antigen
• four-fold rise in antibody against Vi antigen has been detected seven days following primary immunisation with Vi vaccine
• maximum antibody response is achieved one month following vaccination and persists for about three years
• protection from vaccination may be less if a large number of infective organisms are ingested. Because of the limited protection offered by the vaccine, the importance of scrupulous attention to personal, food and water hygiene must still be emphasised for those travelling to endemic areas

Notes:

• protective antibody titres to Vi antigen fall over time. Re-vaccination is necessary when continuing protection is required. Additional doses of Vi vaccine do not boost serum antibody levels; re-vaccination returns antibody levels to those achieved after the primary immunisation
• non-conjugated polysaccharide vaccines are poorly immunogenic in infants and young children. There is little definitive data on the efficacy of Vi vaccine in children aged less than 18 months