Long term trends introduce a potential bias when evaluating the impact of the pneumococcal conjugate vaccination programme in England and Wales

Stefan Flasche, M. Slack, Elizabeth Miller

Research output: Contribution to journalArticlepeer-review

24 Citations (Scopus)


A pneumococcal conjugate vaccine (PCV7) was introduced into the United Kingdom’s childhood immunisation schedule in September 2006. Evaluation of its impact on the incidence of invasive pneumococcaldisease (IPD) as assessed by routine reports of
laboratory-confirmed cases should take into account possible long-term trends due to factors like changes in case ascertainment. To this end, we compared pre-PCV7 trends in reported IPD incidence in England and Wales identified by blood culture with those for two other bacteraemias, Escherichia coli and non -pyogenic streptococci, for which there has not been any public health intervention. While no trend was detected in
the age group 65 years and older, there was an annual increase of 3% and 11% in those aged under five years and between five and 64 years, respectively, which was similar for IPD and the other two pathogens. After PCV7 introduction, a continuing trend was only found for non-pyogenic streptococci in under five year-olds. These trends in the incidence for bacteraemias for which there has been no intervention could suggest
that there have been changes in case ascertainment because of increased reporting or blood culturing. Accounting for them will improve the evaluation of the impact of PCV7 on IPD.
Original languageEnglish
Article number19868
Pages (from-to)13-18
Number of pages6
Issue number20
Publication statusPublished - 19 May 2011


  • pneumococcal conjugate vaccine
  • PCV7
  • childhood immunisation
  • non-pyogenic streptococci
  • long term trends
  • potential bias
  • evaluation
  • pneumococcal conjugate vaccination
  • england
  • wales

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