Immunological and Epidemiological Aspects of the Immunogenicity of Streptococcus Pneumoniae Serotype 3 Capsular Polysaccharide in Pneumococcal Vaccines

The introduction of pneumococcal vaccines into national immunization programmes around the world has reduced the incidence of pneumococcal vaccine serotypes, but had no influence on the incidence of Streptococcus pneumoniae serotype 3 included in their composition. The results of evaluation of epidemiological efficacy and immunogenicity of capsular polysaccharide of S. pneumoniae serotype 3 capsular polysaccharide (CP) in conjugated and polysaccharide pneumococcal vaccines are contradictory. Some studies have shown the effectiveness of vaccination, other studies indicate insufficient immunogenicity and prophylactic efficacy of S. pneumoniae serotype 3 CP. The authors’ analysis of the results of clinical studies showed that the prophylactic efficacy of S. pneumoniae serotype 3 CP depends on the type of vaccine, nosological form of the disease, age, immunization schedule. According to the literature data, the most informative parameter of the protective activity of S. pneumoniae CP in pneumococcal vaccines, including serotype 3, is opsonophagocytosis. The experimental data of the low immunogenicity of serotype 3 CP, presumably associated with an unusual way of synthesis of its CP, are considered. To increase the im muno genicity of S. pneumoniae serotype 3 CP, the use of synthetic oligosaccharides of a strictly defined chemical structure corresponding to the protective fragments of serotype 3 CP and conjugated with a carrier protein for induction of T-dependent immune response and immunological memory is promising.