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.

Prevalence and risk factors of nasopharyngeal carriage of Streptococcus pneumoniae in healthy children in Japan.

The findings of this study revealed a 22% prevalence of Streptococcus pneumoniae among healthy children in Japan; the prevalence tended to increase with age. We identified attendance at day-care facilities and the presence of older siblings as the major risk factors associated with pneumococcal carriage. A significant decrease in pneumococcal colonization was observed among children during the summer; however, a seasonal variation was independent of various factors. Our findings suggest that prior immunization with heptavalent pneumococcal conjugate vaccine within the current recommended schedule is required for children exposed to these risk factors.