Impact of more than a decade of pneumococcal conjugate vaccine use on carriage and invasive potential in Native American communities

Abstract

Background: We assessed the impact of 12 years of pneumococcal conjugate vaccine (PCV7) use on pneumococcal nasopharyngeal carriage and serotype-specific invasive disease potential among Native Americans.

Methods: Families were enrolled in a carriage study from 2006 to 2008; nasopharyngeal specimens and risk factor information were collected monthly for 7 visits. Pneumococcal carriage prevalence was compared with that before (1998-2000) and during (2001-2002) PCV7 introduction. We compared invasive disease incidence and carriage prevalence before and after PCV7 introduction to estimate changes in serotype-specific invasive potential.

Results: We enrolled 1077 subjects from 302 households. There was an absolute reduction in carriage prevalence of 8.0% (95% confidence interval [CI], 4.5%-11.4%) in children aged <5 years and 3.1% (95% CI, 1.1%-5.1%) in adults. In children aged <5 years, vaccine-serotype carriage prevalence decreased by 22.8% (95% CI, 20.1%-25.3%), and nonvaccine serotype (NVT) increased by 15.9% (95% CI, 12.4%-19.3%). No significant change was detected in serotype-specific invasive potential after PCV7 introduction.

Conclusions: Pneumococcal carriage prevalence decreased in all ages since PCV7 introduction; vaccine-serotype carriage has been nearly eliminated, whereas the prevalence of NVT carriage has increased. The increase in the NVT invasive disease rate seems to be proportional to the increase in colonization prevalence.

Figure 1.

Number of nasopharyngeal specimens collected and percentage positive for pneumococcus by age strata.

Figure 2.

Comparison of absolute carriage prevalence by type in children aged <5 years (years 1998–2000 vs 2006–2008) and in adults (years 2001–2002 vs 2006–2008). NVT, nonvaccine serotype; VT, vaccine serotype.

Figure 3.

Invasiveness rate ratios by serotype, sorted by increasing variance.