ABSTRACT
Introduction To become familiar with the three generations of pneumococcal vaccines, It IS important to review the immunological basis upon which they are believed to function. The 23-valent pneumococcal polysaccharide 'grandparent' vaccine contains T -cell-independent antigens capable only of inducing a restricted immunoglobulin G (IgG) response with poor immunological memory 111. The 7-valent pneumococcal conjugate 'parent' vaccine acts by T -cell-dependent mechanisms to induce T -helper cells to stimulate polysaccharide-specific B cells to maturation. These become either antibody-producing plasma cells or memory cells. While there is a degree of crossreactivity between pneumococcal serotypes within serogroups, essentially a 7-valent vaccine can be relied upon to cover for the seven serotypes included, a 9-valent vaccine to cover the nine serotypes, etc. Pneumococcal conjugates will be the dominant pneumococcal vaccines for the time being. The next generation will be protein vaccines, but their mechanism of action is as yet barely understood.
