Nasopharyngeal colonization with heptavalent pneumococcal conjugate vaccine serotypes of Streptococcus pneumoniae with prolonged vaccine dosing intervals.

INTRODUCTION: Universal infant heptavalent pneumococcal conjugate vaccine (PCV-7) immunization, dosed near to the originally recommended schedule of a 3-dose series in the first 6 months of life, then a booster between 12 and 15 months, should reduce nasopharyngeal (NP) carriage of Streptococcus pneumoniae (Spn) PCV-7 types. The reduced availability of PCV-7 altered immunization schedules, particularly for third and fourth PCV-7 doses. We evaluated NP colonization in relation to originally recommended intervals and numbers of PCV-7 doses.

METHODS: Spn from NP cultures of a cohort of 106 normal children, obtained during 20 months of PCV-7 shortage, were identified and serotyped by standard methods.

RESULTS: Spn was detected in 153 of 418 cultures (37%). Age, >1 sibling, day-care attendance and prolonged PCV-7 dosing intervals were univariate risks for NP detection of PCV-7 types. PCV-7 strains comprised 7 of 15 (47%) of Spn before the first dose, 28 of 36 (78%) and 27 of 41 (66%), respectively, after the first and second dose and then 16 of 36 (44%) and 11 of 25 (44%) after the third and fourth doses. The risk of NP colonization with PCV-7 types was higher with intervals of >3 months between second and third doses and intervals of >8 months between the third and fourth doses. Multivariate analysis showed prolonged interval after the second and third PCV-7 doses and day-care attendance as risk factors for NP detection of PCV-7 strains.

CONCLUSION: Although PCV-7 serotypes were detected less after third and fourth PCV-7 doses, longer dosing intervals, particularly in day-care attendees, were associated with higher risk of PCV-7 detection in the NP.