There are interesting dynamical aspects to the routine vaccination of children with pneumococcal conjugate vaccines (PCVs). Through protection against colonisation of the nasopharynx by vaccine serotypes (depending on vaccine formulation 7,10 or 13 out of more than 90 serotypes) PCVs not only reduce transmission of the respective types which induces substantial herd effects but they also create an ecological niche which is instantaneously filled by serotypes that are untargeted by PCVs. Hence the serotype specific propensity to cause disease is a crucial factor to the success of PCVs.
We have been using mathematical models of varying complexity to address questions around pneumococcal conjugate vaccination. We have been exploring how host immunity may shape the coexistence of pneumococci despite their competition and are investigating to what extend the competition from non-vaccine serotypes facilitates the success of PCVs with limited valency. With collaborators from Kenya and Vietnam we have used dynamical models to predict post vaccination changes in pneumococcal epidemiology and to assess the impact of vaccination. We used these and similar models to explore to what extend delayed introduction due to limited vaccine stocks can offset the benefit of catch-up campaigns that include either all children under 1, 2 or 5 years of age. We have developed statistical models to describe the general relationship of carriage prevalence in adults and children and performed Bayesian meta-analyses to estimate the duration of protection from PCVs. Furthermore we have investigated factors that drive the mid to long term impact of PCVs.
Le Polain de Waroux O, Flasche S, Prieto-Merino D, Edmunds WJ (2014) Age-dependent prevalence of nasopharyngeal carriage of streptococcus pneumoniae before conjugate vaccine introduction: a prediction model based on a meta-analysis. PLoS One 9: e86136. doi:10.1371/journal.pone.0086136.
Flasche S, Edmunds WJ, Miller E, Goldblatt D, Robertson C, et al. (2013) The impact of specific and non-specific immunity on the ecology of Streptococcus pneumoniae and the implications for vaccination. Proc Biol Sci 280: 20131939. doi:10.1098/rspb.2013.1939.
Choi YH, Jit M, Flasche S, Gay N, Miller E (2012) Mathematical modelling long-term effects of replacing Prevnar7 with Prevnar13 on invasive pneumococcal diseases in England and Wales. PLoS One 7: e39927. doi:10.1371/journal.pone.0039927.
Flasche S, Slack M, Miller E (2011) Long term trends introduce a potential bias when evaluating the impact of the pneumococcal conjugate vaccination programme in England and Wales. Eurosurveillance 16: 1–6.
Weinberger DM, Harboe ZB, Flasche S, Scott JA, Lipsitch M (2011) Prediction of serotypes causing invasive pneumococcal disease in unvaccinated and vaccinated populations. Epidemiology 22: 199–207. doi:10.1097/EDE.0b013e3182087634.