Changes in Streptococcus pneumoniae serotypes in the nasopharynx of Japanese children after inoculation with a heptavalent pneumococcal conjugate vaccine.

In this study, we prospectively investigated changes in Streptococcus pneumoniae serotypes among Japanese children after heptavalent pneumococcal conjugate vaccine (PCV7) inoculation. We acquired nasopharyngeal swabs from the children at each routine PCV7 inoculation and again at least 2 months after the last PCV7 inoculation. We defined 2 periods with regard to each culture: the inoculation period as "the period of pre- or incomplete vaccination" and post-inoculation as "the period of post- or completed vaccination." The prevalence of vaccine-type (VT) pneumococci was significantly reduced from 9.5% in the inoculation-period cultures to 2.9% in the post-inoculation cultures (P < 0.01). There was no statistical difference in the prevalence of non-vaccine-type pneumococci between the inoculation-period and post-inoculation cultures (24.1% versus 23.4%). The protection of PCV7 against nasopharyngeal colonization was inferred from the decrease in VT carriage post-inoculation. The decrease in VT carriage may be conducive to reducing VT transmission within the study area.