VT isolates were almost five times less likely to

be acquired de novo in the vaccinated than in the control group (OR, 4.80; 95% CI, 2.81–8.24) ( Table 4). Unmasking of NVTs was inexistent in the control and reached 100% in the vaccinated group (P < 0.001) ( Table 4). Epidemiological studies in numerous countries have demonstrated the replacement of VT by NVT isolates in the nasopharynx of children immunized with a multi-valent pneumococcal conjugate vaccine [10], [12], [13], [29], [30] and [31]. The nasopharynx is the immediate source of disease-causing pneumococci and the appearance of NVT isolates with pathogenic potential has raised concerns [32] and [33]. In 2006, Barzilay et al. reported a 62% reduction in invasive pneumococcal disease caused by vaccine types in children immunized with a single PCV7 dose at 5–8 months of age [18]. In the same year, a matched case-control study observed a 93% effectiveness selleck chemicals of a single PCV7 dose in children vaccinated at 12–23 months of age [19]. However, the effect on nasopharyngeal colonization – the launching pad for pneumococcal disease – was not assessed. The present study evaluated the effect of a single dose of PCV7 on the nasopharyngeal

carriage of pneumococci in day care center attendees in Lisbon, Portugal, i.e., a study population in which the pneumococcal carriage rates are known to be high [34], [35], [36] and [37]. Immunized children in this study were between 12 and 24 months, an age at which a single dose showed 93% effectiveness regarding invasive disease caused by vaccine types [19]. Multiple pneumococcal isolates were analyzed, enabling the study learn more of ecological phenomena that contribute to the serotype changes in the nasopharynx. At the population level, although the overall number of pneumococcal isolates from single and multiple carriers was similar in both sampling periods in the vaccinated and control groups (Table 1), differences became apparent once the isolates were divided into VTs and NVTs. In the vaccinated group, within a month,

CYTH4 a single PCV7 dose led to a serotype replacement phenomenon between VT and NVT isolates, both in single and multiple carriers, in contrast to the control where no replacement phenomenon was detected (Table 2 and Table 3). At the individual level, a serotype replacement event could also be observed. After vaccination with a single dose, with the exception of two children, VT isolates were not present or were found as minor serotypes and, in parallel, NVTs were detected as dominant serotypes (Fig. 1, children A to K). We show that a serotype replacement phenomenon took place 1 month after a single dose of PCV7, not only at the population but also at the individual level where vaccine types became minor serotypes co-colonizing with the emergent NVTs. Competition between serotypes in vaccinated children leads to serotype replacement of VT by NVT serotypes [38].