Reduced diphtheria toxoid

Reduced diphtheria toxoid is a detoxified form of the diphtheria toxin used as an antigen in combination vaccines, most commonly in Tdap (tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine) formulations. It stimulates the immune system to produce antibodies against *Corynebacterium diphtheriae*, providing protection against diphtheria. The "reduced" designation refers to a lower concentration of the antigen compared to pediatric formulations (DTaP), making it suitable for booster immunization in adolescents and adults. Reduced diphtheria toxoid is not administered alone but as part of combination vaccines such as Adacel and Boostrix[1][3][5]. These vaccines are indicated for active booster immunization against tetanus, diphtheria, and pertussis[1][3][5]. The mechanism of action involves induction of immunity by promoting antibody production specific to the bacterial toxin.