Effect of Pneumococcal Conjugate Vaccine on Nasopharyngeal Colonization among Immunized and Unimmunized Children in a Community‐Randomized Trial

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Abstract
Background.Pneumococcal conjugate vaccines (PCVs) prevent vaccine serotype (VT) invasive disease; nonvaccine serotype (NVT) disease increases modestly. The impact of PCV on nasopharyngeal (NP) colonization is essential to understanding disease effects. Methods.We conducted a community-randomized controlled trial with catch-up vaccination through age 2 years investigating the effect of 7-valent PCV (PnCRM7) on NP colonization among American Indian infants and their unvaccinated contacts. Infants receiving blinded vaccine at 2, 4, 6, and 12–15 months of age had NP cultures obtained at age 7, 12, and 18 months. Serotype-specific colonization was detected by immunoblot. Results.We enrolled 566 vaccinated and 286 unvaccinated children from 511 households and collected 5157 specimens, of which 3525 (68.4%) had pneumococcus. PnCRM7 vaccinees were less likely to be colonized with VT (odds ratio [OR], 0.40 [95% confidence interval {CI}, 0.23–0.67]) but were more likely to be colonized with NVT pneumococci (OR, 1.67 [95% CI, 1.02–2.78]). PnCRM7 vaccinees were less densely colonized with VT strains than control vaccinees (OR, 0.61 [95% CI, 0.38–0.99]). Day care–attending unvaccinated children in PnCRM7 communities were less likely to have VT colonization than those in control communities (OR, 0.27 [95% CI, 0.07–1.07]). Conclusions.PnCRM7 reduces the risk of VT acquisition and colonization density but increases the risk of NVT acquisition among vaccinees and their household contacts.

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