Anthrax is a disease caused by infection with spore-forming bacteria, which can enter the body through cuts in the skin, ingestion of undercooked meat, or inhalation. The anthrax vaccine helps prevent anthrax infection through exposure to an antigen protein that develops immunity but does not contain live or killed bacteria. Common mild side effects include redness, swelling, soreness, or itching near the injection site as well as tiredness. The vaccine is given as a series of 6 shots over 18 months followed by annual boosters to maintain protection.