The complexity of serotype replacement of pneumococci.

Pneumococci respond extremely rapidly to the vaccine pressure created by the conjugate vaccines (PCVs). Vaccine serotypes are disappearing, meanwhile new, often previously very rare types are emerging, and it is difficult to establish what makes certain serotypes more successful in replacement. The situation is very complex: every serotype has different antibiotic sensitivity or invasive capacity. However, despite this dynamic serotype rearrangement, the overall pneumococcal carriage rate remains quite stable, suggesting that these bacterial species can be considered as a commensal colonizer.