The effect of vaccination on Streptococcus pneumoniae resistance.

Following the introduction of the 7-valent pneumococcal conjugate vaccine (PCV-7) in the routine immunization schedule of US children, the morbidity and mortality associated with Streptococcus pneumoniae infections have changed considerably. Post-licensure data from the United States have confirmed that PCV-7 has significantly decreased the incidence of vaccine-type susceptible and antibiotic-resistant invasive pneumococcal diseases, community-acquired respiratory infections, and nasopharyngeal colonization in vaccinated individuals and their contacts. An unintended consequence of immunization with PCV-7 is the simultaneous increase in the carriage rates of non-vaccine-serotype pneumococci (some of which are highly antibiotic-resistant) among vaccinated children (ie, replacement phenomenon). Neither the implications of increased non-vaccine-type colonization nor the additional role of inappropriate antibiotic use in this process is clearly understood, but the greatest concern is that replacement colonization may result in replacement disease. Future vaccination with PCV-7 in European countries could provide additional information.