Pneumococcal disease and the impact of pneumococcal conjugate vaccines

This thesis addresses various aspects on pneumococcal disease, pneumococcal conjugate vaccines (PCVs) and the societal impact of PCV implementation in children. Implementation of 7-valent pneumococcal conjugate vaccine (PCV7) in the Dutch national immunization program for infants led to a shift from vaccine to non-vaccine serotypes (i.e. replacement disease) in invasive pneumococcal disease (IPD). This shift was observed in all age groups, including non-vaccinated persons, due to indirect effects.Indirect were caused by a reduction in nasopharyngeal colonization of vaccine serotypes in children and subsequent transmission (i.e. herd effects). Also after PCV7 was replaced by a 10-valent pneumococcal conjugate vaccine (PCV10) we observed herd effects for extra serotypes covered by PCV10.Replacement disease following PCVs was primarily caused by expansion of pre-existing non-vaccine serotypes (NVT) rather than capsular switch variants.Despite replacement disease IPD incidence has decreased dramatically in children