Saccharide conjugate vaccines which use diphtheria toxoid or tetanus toxoid as a carrier protein can confer protection against lethal challenge by diphtheria toxin or tetanus toxin. Thus, in addition to protecting against the bacteria whose saccharides have been attached to the carrier, such conjugate vaccines can also be used to protect against diphtheria and tetanus, so the diphtheria toxoid and tetanus toxoid components of current complex combination vaccines may be superfluous. Therefore the antigenic complexity of these vaccines can be reduced without reducing their breadth of protection, and removing these superfluous components creates space in the vaccine for adding immunogens for protecting against further pathogens. The same effect is not seen with a CRM197 carrier, but this observation makes this carrier more attractive for conjugate vaccines which are given concomitantly with infant combination vaccines that contain Dt and Tt.
