Streptococcus pneumoniae serotype replacement in nasopharyngeal colonization in children vaccinated with PCV7 in Mexico

To assess the impact of pneumococcal conjugate vaccine (PCV7) immunization on pneumococcal nasopharyngeal colonization with S. pneumoniae (SPN). We studied two groups with different vaccination schedules, group I (2-6 months of age) 3+1 and group II (7 -11 months) 2+1, with a booster at 15 months. Nasopharyngeal cultures were obtained before administering each vaccination dose and after booster. Paired and global analyses were carried out of the proportions of children colonized by SPN, vaccine serotype, no vaccine serotype and resistance to penicillin. A total of 183 children were enrolled; 93 in group I and 90 in group II. In group I, there was a decrease in vaccine serotypes in the third sample. In group II, there was an increase in non-vaccine serotypes and a decrease in vaccine serotypes before booster. Both groups showed a trend toward decreased resistance to penicillin. PCV7 caused serotype replacement in nasopharyngeal colonization before the booster.