Research Article: Effect of Pneumococcal Conjugate Vaccination on Serotype-Specific Carriage and Invasive Disease in England: A Cross-Sectional Study

Date Published: April 5, 2011

Publisher: Public Library of Science

Author(s): Stefan Flasche, Albert Jan Van Hoek, Elizabeth Sheasby, Pauline Waight, Nick Andrews, Carmen Sheppard, Robert George, Elizabeth Miller, Keith P. Klugman

Abstract: A cross sectional study by Stefan Flasche and coworkers document the serotype replacement of Streptococcus pneumoniae that has occurred in England since the introduction of PCV7 vaccination.

Partial Text: Streptococcus pneumoniae is a bacterium that frequently colonises
the human nasopharynx. Apart from disease outcomes such as sinusitis, otitis media,
and community-acquired pneumonia, which result from direct spread from the
nasopharynx, the pneumococcus can invade the bloodstream and cause septicaemia,
meningitis, and invasive pneumonia. Most carriage episodes, however, do not result
in either local or systemic disease. It is believed that the propensity to cause
invasive disease in healthy individuals—termed invasiveness—is largely
determined by the characteristics of the pneumococcus’ polysaccharide capsule,
although the explicit underlying mechanisms are yet to be identified [1],[2]. On the
basis of the immune response to differences in capsular polysaccharide structure,
more than 90 serotypes causing invasive disease have been described [3].

400 individuals were enrolled between 24 April 2008 and 9 November 2009. One
participant withdrew before being swabbed and in 17 individuals swabbing had to be
aborted early; these 18 participants were excluded from further analyses. The
demographic features of the remaining 382 participants were similar to the
participants in the 2001/2002 study, apart from the proportion of households with at
least one smoker, which was lower in the more recent study (Table 1). Of 180 children eligible for catch-up
or infant vaccination only four were unvaccinated.

Our study documents the changes in carried pneumococci following the introduction of
PCV7 in England and relates these to concomitant changes in disease in order to
assess the invasiveness potential of the serotypes now predominating carriage. This
knowledge is essential for understanding replacement pneumococcal disease and
provides insight into the likely population impact of higher valency vaccines. As
reported elsewhere [13],[14], we found a major reduction in VT carriage in vaccinated
children under 5 y, but no overall change in carriage prevalence due to replacement
with NVTs. In contrast, there was an overall reduction in IPD in this age group,
illustrating that the outcome of the PCV programme as expressed in IPD is determined
by the invasiveness potential of the individual NVTs emerging in carriage. Overall
carriage prevalence in older unvaccinated siblings and parents was somewhat higher
post-PCV7 as found in parents of 2 y olds in a vaccine trial with a 2-dose or a
2+1-dose schedule in the Netherlands [23]. This finding was due to a large
increase in NVT and a smaller nonsignificant reduction in VT carriage. However, IPD
in these older age groups has not shown an overall increase in the UK [24], indicative of
the lower overall invasiveness of the replacing NVTs.



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