Impact of thirteen-valent pneumococcal conjugate vaccine on nasopharyngeal carriage in healthy children under 24 months in Okinawa, Japan.

In November 2013, a 13-valent pneumococcal conjugate vaccine (PCV13) for all infants aged younger than 5 years was incorporated into the Japan national immunization program. An annual survey of nasopharyngeal carriage rates was performed on healthy infants aged 2-24 months from Okinawa, Japan to evaluate the effect of PCV13 on pneumococcal colonization. Of 756 evaluable infants, 203 pneumococcal strains were detected in 193 infants. The overall nasopharyngeal carriage rate was 25.5%, which was not different from our previously reported isolation rate before the introduction of PCV13. The main serotypes of the Streptococcus pneumoniae strains are 15A (18.2%), non-typeable (14.8%), and 15B (11.8%). The carriage rates of pneumococcal strains with 7-valent pneumococcal conjugate vaccine serotypes and PCV13 serotypes were 3.0% and 9.9%, respectively. These values were significantly lower than we reported before the introduction of PCV13. However, the carriage rates of non-PCV13 serotypes have increased. Multivariate logistic regression analysis suggested that siblings and day care attendance are risk factors for pneumococcal carriage.