Abstract
The efficacy of vaccines against major encapsulated bacterial pathogens –Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae type b (Hib) – has been significantly enhanced by conjugating the respective polysaccharides with different carrier proteins: diphtheria toxoid; non-toxic cross-reactive material of diphtheria toxin197, tetanus toxoid, N. meningitidis outer membrane protein, and non-typeable H. influenzae-derived protein D. Hib, meningococcal, and pneumococcal conjugate vaccines have shown good safety and immunogenicity profiles regardless of the carrier protein used, although data are conflicting as to which carrier protein is the most immunogenic. Coadministration of conjugate vaccines bearing the same carrier protein has the potential for inducing either positive or negative effects on vaccine immunogenicity (immune interference). Clinical studies on the coadministration of conjugate vaccines reveal conflicting data with respect to immune interference and vaccine efficacy.