Anthrax vaccine is a vaccine against the infectious isease, anthrax. Anthrax is caused by the spore-forming bacterium Bacillus anthracis, that most commonly occurs in wild and domestic mammals. Anthrax also occurs in humans when they are exposed to infected animals, hides, or tissue from infected animals, or when they are directly exposed to B. anthracis. Depending on the route of infection, anthrax disease can occur in three forms: cutaneous, inhalational, and rarely, gastrointestinal.