Background In April 2010, 13-valent pneumococcal conjugate vaccine (PCV13) replaced PCV7 in the infant immunisation schedule in England and Wales. Despite limited serotype replacement in invasive pneumococcal disease (IPD) during the first four post-PCV13 years, non-vaccine type (NVT) IPD increased substantially in 2014/15. We undertook a carriage study in 2015/ 16 to help understand the reasons for this increase. Methods and findings Families with a child aged <5 years attending a participating general practice in Gloucestershire or Hertfordshire were invited to provide nasopharyngeal swabs from all consenting members. Swabs from 650 individuals (293 under five, 73 five to twenty and 284 >twenty years) were cultured and serotyped for Streptococcus pneumoniae. Results were compared with those from three previous household studies conducted in the same populations between 2001 to 2013, and with the serotypes causing IPD to estimate case-carrier ratios (CCRs). Overall carriage prevalence did not differ between the four carriage studies with reductions in vaccine-type carriage offset by increases in NVT carriage. While no individual NVT serotype showed an increase in CCR from 2012/13, the composition of the serotypes comprising the NVT group differed such that the overall CCR of the NVT group had significantly increased since 2012/13. Carriage of two PCV13 serotypes, 3 and 19A, was found in 2015/16 (3/650 = 0.5% and 2/650 = 0.3% respectively) with no overall reduction in carriage prevalence of PCV13-7 serotypes since 2012/13, though 6C prevalence, a vaccine-related serotype, had reduced from 1.8% in 2012/13 to 2/648 (0.3%) in 2015/16, p = 0.013. Conclusions There was continuing evolution in carried NVTs six years after PCV13 introduction which, in addition to being vaccine-driven, could also reflect natural secular changes in certain NVTs. This poses challenges in predicting future trends in IPD. Elimination of carriage and disease due to serotypes 3 and 19A may not be achieved by PCV13.
Bibliographical noteFunding Information:
The report is based on independent research commissioned and funded by the NIHR Policy Research Programme (National Vaccine Evaluation Consortium, Grant number 039/0031-grant holder EM). Albert Jan van Hoek’s research is partly supported by the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Immunisation at the London School of Hygiene & Tropical Medicine in partnership with Public Health England (PHE), grant number HPRU-2012-10096. The views expressed in the publication are those of the authors and not necessarily those of the NHS, the NIHR, the Department of Health, arms’ length bodies, other government departments, the London School of Hygiene & Tropical Medicine or Public Health England. The funders had no input study design, analysis of the data or writing of the manuscript. We thank the Vaccine Research Nurse teams in Gloucester and Hertfordshire, Tao Haskins-Coulter who assisted with study coordination and the administrative team in the Immunisation Department at Public Health England for their assistance in the conduct of the study. We acknowledge current and previous members of the Respiratory and Vaccine Preventable Bacteria Unit, PHE National Infection Service for routine Streptococcus pneumoniae serotyping data, and Sarah Collins and Shamez Ladhani for facilitating access to the 2015/16 serotyped IPD data.
© 2018 Southern et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.