Pneumococcal polysaccharide vaccines.

Pneumococcal infections are major causes of morbidity and mortality in children throughout the world. For this reason and because of the increasingly frequent isolation of multiply resistant pneumococci of the serotypes most often causing infection in childhood, prophylactic immunization offers the best prospect of reducing the incidence of such infections in the future. Studies of the immune system of humans have shown that immunologic maturation continues throughout the first decade of life and that responsiveness to some purified bacterial polysaccharides may be delayed until several years after birth. Vaccines of such capsular polysaccharides conjugated chemically to protein have been found to be immunogenic at an earlier age and to stimulate the development of IgM and IgG antibodies and of "immunologic memory." Current investigations suggest that administration of polyvalent vaccines of polysaccharide-protein conjugates in infancy followed by the administration of vaccines of purified polysaccharides after the age of 10 years offers the prospect of reducing significantly the incidence of pneumococcal infections.