Diphtheria toxoid is usually adsorbed onto an adjuvant to increase its immunogenicity. It is highly effective in inducing antibodies that will prevent disease, although antibodies may … Adjuvants are either aluminium phosphate or aluminium hydroxide.

The vaccine antigen is prepared by treating a cell-free toxin preparation with formaldehyde.

ADACEL(R): 10 to 64 years old: 0.5 mL intramuscularly once -Routine booster vaccination should be 5 or more years after the last recommended dose of the diphtheria, tetanus, and acellular pertussis vaccine adsorbed (DTaP) series. -May use as a booster dose 8 years after the first tetanus toxoid, reduced diphtheria and acellular pertussis vaccine, adsorbed (Tdap) dose.

This converts it into diphtheria toxoid, which is safe.

https://www.historyofvaccines.org/index.php/content/articles/diphtheria -May use for tetanus prophylaxis in wound management if at least 5 years have elapsed since a previous tetanus toxoid containing vaccine …

Diphtheria toxoid is a purified preparation of inactivated diphtheria toxin.