Whilst one of the first microbial pathogens to be identified (Sternberg / Pasteur, 1880) Streptococcus pneumoniae is still a major cause of morbidity and mortality.
Although there are at least 93 different serotypes, characterized by the capsular polysaccharide structure, 13 of these serotypes causes more than 80% of pneumococcal disease in children.
Current pneumococcal vaccine formulations are based on eliciting serotype-specific polysaccharide antibody responses.
Multivalent pneumococcal polysaccharide-protein conjugate vaccines have been successful in preventing pneumococcal disease in young children and immunocompromised individuals, among whom purely non-conjugated polysaccharide vaccines had limited efficacy.
Meta-analysis has shown that the efficacy of PCV against vaccine-serotype specific invasive pneumococcal disease and acute otitis media was 89% and 55%, respectively. In addition, efficacy against all-cause radiographic confirmed pneumonia was 30%.
PCV has also been associated with reduction in risk of acquisition of S. pneumoniae in vaccinated children. This has been associated with reduced transmission of pneumococcus in the community, and consequent reduced risk of developing pneumococcal disease in unvaccinated individuals in the community (i.e. “herd protection”).
The main consequence of the herd protection is that after introduction of PCV in universal vaccination programs, a greater reduction of disease than predicted by efficacy studies was observed.
Future generations of pneumococcal vaccine may include targeting epitopes which are common to most serotypes, immunogenic in high-risk groups and able to eliciting anamnestic immune responses.