Serotype replacement in perspective.

An increase in the incidence of invasive pneumococcal disease (IPD) caused by non-vaccine serotypes (NVTs) (serotype replacement) has been observed since the introduction of the seven-valent pneumococcal conjugate vaccine (PCV7), primarily in the elderly, HIV-positive adults, and children with underlying medical conditions. In children aged <5 years, only a slight increase in replacement disease due to NVTs has been observed, but the relationship of changes in serotype carriage to replacement disease is not well understood. Predominant post-PCV7 NVTs include serotypes 15, 19A, and 33F, but the increasing antibiotic resistance of 19A is of particular concern in both vaccinated and unvaccinated populations.