toxoid

A toxoid is an inactivated toxin used as a vaccine component. Toxoids are produced by detoxifying the toxin so it loses its harmful biological activity but retains its structure enough to provoke an immune response. When administered, a toxoid stimulates the immune system to produce neutralizing antibodies that can block the effects of the toxin if a person is subsequently exposed. Because the toxin is inactivated, toxoid vaccines do not cause the disease they protect against, although they can cause mild local or systemic reactions.

The best-known toxoids are diphtheria toxoid and tetanus toxoid, which are commonly combined in vaccines such as DTaP for children and Td or Tdap for older individuals. Many immunization programs rely on these toxoid components to protect against diphtheria and tetanus, diseases caused by toxin-mediated damage rather than by infection alone. Some vaccines used to prevent pertussis incorporate a detoxified pertussis toxin component as part of broader antigen formulations (acellular pertussis), but protection against pertussis relies on multiple antigens in the vaccine.

Production typically involves detoxifying the bacterial toxin with chemical agents (historically formaldehyde is common) and then purifying the resulting toxoid for formulation with adjuvants to enhance immunogenicity. Toxoid vaccines generally require booster doses to maintain protective antibody levels, with schedules varying by country. Safety profiles are favorable, with most adverse effects including mild injection site reactions or fever; serious reactions are rare.