Abstract
Although mean efficacy of multivalent pneumococcus vaccines has been intensively studied, variance in vaccine efficacy (VE) has been overlooked. Different net individual protection across settings can be driven by environmental conditions, local serotype and clonal composition, as well as by socio-demographic and genetic host factors. Understanding efficacy variation has implications for population-level effectiveness and other eco-evolutionary feedbacks. Here I show that realized VE can vary across epidemiological settings, by applying a multi-site-one-model approach to data post-vaccination. I analyse serotype prevalence dynamics following PCV7, in asymptomatic carriage in children attending day care in Portugal, Norway, France, Greece, Hungary and Hong-Kong. Model fitting to each dataset provides site-specific estimates for vaccine efficacy against acquisition, and pneumococcal transmission parameters. According to this model, variable serotype replacement across sites can be explained through variable PCV7 efficacy, ranging from 40% in Norway to 10% in Hong-Kong. While the details of how this effect is achieved remain to be determined, here I report three factors negatively associated with the VE readout, including initial prevalence of serotype 19F, daily mean temperature, and the Gini index. The study warrants more attention on local modulators of vaccine performance and calls for predictive frameworks within and across populations.
Highlights
Over the last 20 years, the global epidemiological dynamics of Streptococcus pneumoniae have been under intense investigation
Results from an early vaccine trial[11] in Gambia, West Africa, showed that vaccine serotype carriage following vaccination decreased in children who had received two doses of the vaccine, but was accompanied by an increase in non-vaccine type (NVT) carriage
Data were extracted from 6 different cross-sectional studies on pneumococcus prevalence before and after vaccination with PCV7: the studies are summarized in Tables 1 and 2
Summary
Over the last 20 years, the global epidemiological dynamics of Streptococcus pneumoniae have been under intense investigation. As the net benefit of vaccination critically depends on the balance between vaccine protection and serotype replacement, and the complex relationship between carriage and disease, an important challenge in pneumococcus epidemiology remains to understand and predict post-vaccination dynamics, going beyond descriptive approaches[22, 23]. This includes capturing variation between settings under the same mechanistic framework of pneumococcus transmission. Accurate estimates of vaccine efficacy against serotype acquisition are crucial to subsequently predict or interpret impact on pneumococcal disease[22]
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