Salmonella Typhi: The typhoid fever vaccine market is significant, attractive, and strategic to Matrivax. S. Typhi, the causative agent of typhoid, or enteric, fever alone afflicts >16 million and kills ~600,000 people worldwide each year. S. Typhi produces a single capsular serotype, Vi antigen. The typhoid fever vaccine market is $200 million per year and existing commercial typhoid fever vaccines have clear limitations. Ty21a is a three or four dose, oral, live attenuated vaccine while Typhim-Vi® is a polysaccharide, parenteral vaccine administered in single-dose that can cause local reactogenicity and does not elicit a ‘memory’ immune response. In children under 2 years of age, Typhim Vi is ineffective at eliciting immunological memory and protective responses. Both vaccines confer variable, ~70%, protective efficacy and are not licensed in <2 year-old children or used for routine immunization. However, a Vi–protein conjugate vaccine has been shown to be highly immunogenic and to confer protection to 2 year-old children.