Serotype replacement in Streptococcus pneumoniae after conjugate vaccine introduction: impact, doubts and perspective for new vaccines

The licensed seven-valent pneumococcal conjugate vaccine has successfully reduced invasive pneumococcal disease (IPD) in the USA and in all countries in which it was introduced into national immunization programs, but an increase in the incidence of IPD caused by nonvaccine serotypes has been observed in some areas. This review extended investigation into the effects of PCV7 vaccination on the dynamics of IPD and on the epidemiological picture of circulating serotypes, focusing on mechanisms of pneumococcal escape from vaccination, their impact in terms of reduced effectiveness of PCV7 and the perspective for new vaccines.