Pneumococcal carriage in children and adults two years after introduction of the thirteen valent pneumococcal conjugate vaccine in England

Background/Aims: In April 2010 the 7-valent pneumococcal conjugate vaccine (PCV7) was replaced by the 13-valent PCV. We investigated pneumococcal carriage in children eligible for PCV7 or PCV13 and their household contacts. Methods: Eligible families in Hertfordshire and Gloucester were identified and a nasopharyngeal swab obtained from consenting household members between July 2012 and March 2013. Samples were cultured for Streptococcus pneumoniae and serotyped by standard methods. For each serotype the ratio of its prevalence in invasive pneumococcal disease (IPD) to its carriage prevalence (case:carrier ratio, CCR) was calculated. Results were compared with previous carriage studies in 2001/2002 and 2008/2009, before and after PCV7 introduction. Results: 217 households were included. Among <5-year olds 47.7% (95% confidence interval 41.8-53.5) were carrying a pneumococcus compared with 51.0% (95% CI: 44.0-58.0) in 2008/2009 and 48.4% (95% CI: 44.1-52.7) in 2001/2002. The odds of carrying a PCV7 serotype was significantly reduced in 2008/2009 (0.07,95% CI: 0.03-0.16) and 2012/2013 (0.01 95% CI: 0.00-0.07) relative to 2001/2002, while the odds of carrying any of the extra six PCV13 serotypes increased after PCV7 introduction (1.38, 95%CI: 0.73-2.59) but declined significantly after PCV13 introduction (0.05, 95%CI: 0.01-0.37). The CCRs for the frequently carried serotypes were relatively low, with the highest CCR observed for serotypes 7F, 19A, 3, 8, and 33F. Across the three carriage studies, CCR estimates were stable for nearly all serotypes. Conclusion: Carriage of additional PCV13 serotypes has rapidly reduced post-PCV13 introduction in both vaccinated and unvaccinated individuals with a continued decline in transmission of PCV7 serotypes. Carriage rates in children remain unchanged, but the low CCRs of replacing serotypes would be expected to further reduce overall IPD across all age groups. (C) 2014 Published by Elsevier Ltd.