A substance that is derived from the toxin released by the bacterium that causes the disease tetanus. It is used as a vaccine to prevent tetanus or to help boost the immune response to other vaccines. OR A solution of formaldehyde-deactivated toxin isolated from the bacterium Clostridium tetani. Tetanus toxoid stimulates the production of antitoxin antibodies. This agent may be used as an adjuvant in cancer vaccines.