Review: current and new generation pneumococcal vaccines

Pneumococcal polysaccharide vaccines (PPVs) and conjugate vaccines (PCVs), of which PPV23 and PCV13 are the current front runners, have had a significant, beneficial impact on public health. With regard to PPV23, there has been some debate, however, about its protective efficacy against all-cause pneumonia, as opposed to invasive pneumococcal disease, in high-risk cases. PCVs, on the other hand, have been included in many national immunisation programmes for prevention of severe pneumococcal disease in infants and young children, as well as for adults in various high-risk categories. Although innovative and effective, the protective efficacy of PCVs, the composition of which is based on the geographic prevalence and virulence of pneumococcal serotypes, is limited due to colonisation of the nasopharynx with non-vaccine serotypes. This phenomenon of serotype replacement has provided the impetus for development of new generation recombinant protein and whole cell pneumococcal vaccines with the potential to provide serotype-independent protection. In addition to an overview of the successes and limitations of PPVs and PCVs, this review is focused on emerging and pipeline protein-based and whole cell vaccines, preceded by a consideration of conserved pneumococcal virulence factors which are potential vaccine candidates.