toxoid

thumb|Ruby Hirose researching serums and antitoxins thumb|A poster released by the Central Council for Health Education, spreading awareness about Diphtheria. thumb|A tetanus vaccine is being administered at the Naval medical Center San Diego A toxoid is an inactivated toxin (usually an exotoxin) whose toxicity has been suppressed while retaining its immunogenicity. This is usually achieved by chemical (formalin) or heat treatment. Toxins are secreted by bacteria, whereas toxoids are altered form of toxins; toxoids are not secreted by bacteria. Thus, when used during vaccination, an immune response is mounted and immunological memory is formed against the molecular markers of the toxoid without resulting in toxin-induced illness. Such a preparation is also known as an anatoxin. There are toxoids for prevention of diphtheria, tetanus and botulism.

Toxoids are used as vaccines because they induce an immune response to the original toxin or increase the response to another antigen since the toxoid markers and toxin markers are preserved. For example, the tetanus toxoid is derived from the tetanospasmin produced by Clostridium tetani. The latter causes tetanus and is vaccinated against by the DTaP vaccine. While patients may sometimes complain of side effects after a vaccine, these are associated with the process of mounting an immune response and clearing the toxoid, not the direct effects of the toxoid. The toxoid does not have virulence as the toxin did before inactivation.