Streptococcus pneumoniae can asymptomatically colonize the nasopharynx and cause a diverse range of illnesses. This clinical spectrum from colonization to invasive pneumococcal disease (IPD) appears to depend on the pneumococcal capsular serotype rather than the genetic background. According to a literature review, serotypes 1, 4, 5, 7F, 8, 12F, 14, 18C, and 19A are more likely to cause IPD. Although serotypes 1 and 19A are the predominant causes of invasive pneumococcal pneumonia, serotype 14 remains one of the most common etiologic agents of non-bacteremic pneumonia in adults, even after 7-valent pneumococcal conjugate vaccine (PCV7) introduction. Serotypes 1, 3, and 19A pneumococci are likely to cause empyema and hemolytic uremic syndrome. Serotype 1 pneumococcal meningitis is prevalent in the African meningitis belt, with a high fatality rate. In contrast to the capsule type, genotype is more closely associated with antibiotic resistance. CC320/271 strains expressing serotype 19A are multidrug-resistant (MDR) and prevalent worldwide in the era of PCV7. Several clones of MDR serotype 6C pneumococci emerged, and a MDR 6D clone (ST282) has been identified in Korea. Since the pneumococcal epidemiology of capsule types varies geographically and temporally, a nationwide serosurveillance system is vital to establishing appropriate vaccination strategies for each country.

Streptococcus pneumoniae is a major human pathogen responsible for a majority of bacterial pneumonia as well as invasive pneumococcal diseases (IPD) with high mortality and morbidity. Use of conjugate vaccines targeting pneumococcal capsule has dramatically reduced the incidence of invasive diseases and there are active efforts to further improve the conjugate vaccines. However, in children new pneumococcal vaccines can no longer be tested with placebo-based clinical trials since effective vaccines are currently available. Thus, vaccine studies must depend on surrogate markers of vaccine efficacy. Although traditional antibody levels (e.g., ELISA) are useful as a surrogate marker of protection, they have limitations and a bioassay measuring the capacity of antibodies to opsonize pneumococci has been developed. This opsonophagocytosis assay (OPA) replicates the in vivo mechanism of antibody protection and should therefore better reflect protection by vaccine-induced antibodies. Technical improvements of OPA have made this bioassay rapid, multiplexed and practical for analyzing small samples including those from children. Strong correlations between ELISA and OPA have been observed in many studies of young children. However, poor correlations have been found in some important clinical situations (such as determination of protection by cross-reactive antibodies) and populations (such as elderly adults and immune-deficient patients). In these settings, OPA has become a useful supplementary measure of pneumococcal vaccine immunogenicity. Current efforts to standardize OPA will further expand its uses.

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Streptococcus pneumoniae, or pneumococcus, is a common and virulent pathogen that causes a high burden of clinical disease. All demographic groups are affected; however, older adults and the immunosuppressed are at higher risk for infection of normally sterile body spaces, called invasive pneumococcal disease. Vaccination, both with free-polysaccharide and more recently conjugate protein formulations, has led to reductions in invasive pneumococcal disease. These reductions are not uniform, however, as patients with comorbid illness derive less protection from the free-polysaccharide vaccine. At best, the free-polysaccharide vaccine appears only modestly effective in protecting against nonbacteremic pneumococcal pneumonia. Conjugated protein vaccines stimulate a more vigorous immune response in young children and most adults, as measured by opsonophagocytosis assays. This suggests the conjugate vaccine may offer improved immune protection against both invasive disease and pneumonia; however, large randomized trials with clinical end points are still needed. If proven to be protective, replacement of the current free polysaccharide with conjugate vaccines would likely be cost-effective among adults over 65 years of age and those at higher risk.