Typhoid fever is a life-threatening illness caused by the bacterium, Salmonella Typhi. You can get typhoid fever from foods and beverages contaminated with Salmonella. Typhoid fever is common in most parts of the developing world. The Typhoid vaccine comes in two forms. The oral dose consists of 4 doses taken at two day intervals. It needs to be refrigerated. A booster is recommended every five years. The Typhoid Vi vaccine is a single injection. A booster is recommended every two years for the injectable vaccine.