HAEMOPHILUS-INFLUENZAE TYPE-B CONJUGATE AND COMBINATION VACCINES

Haemophilus influenzae type b (Hib) conjugate vaccines represent a new technology wherein an immunogen is targeted to a specific immune response mechanism. Covalent attachment of the Hib polysaccharide to a protein carrier converts the T cell-independent polysaccharide antigen into a protein-like T cell-dependent antigen. The polysaccharide alone is poorly immunogenic in infants (less than or equal to 12 months old), and conjugation to a protein carrier results in a protein-like antibody response to the Hib polysaccharide in infants. Conjugate vaccines induce mostly IgG antibodies and immunological memory. Later vaccination or natural exposure then induces a booster response to the Hib polysaccharide. These conjugate vaccines have dramatically reduced the incidence of Hib disease in many industrialised countries, and also reduce nasopharyngeal carriage of Hib in unvaccinated children in populations in which the vaccine is used. The Hib conjugates have now been combined with diphtheria and tetanus toxoids and pertussis vaccine to reduce the number of injections required for infants. Finally, the conjugate technology that has permitted the near elimination of Hib disease has now been extended to other invasive encapsulated bacterial pathogens.