BACKGROUND: Infant pneumococcal conjugate vaccines (PCVs) have reduced invasive pneumococcal disease (IPD) due to vaccine-specific serotypes. Predicting future pneumococcal epidemiology is challenging given the complex nature of serotype dynamics and vaccine impact. We developed an intuitive approach to modeling IPD through observed PCV impact in various settings.
METHODS: Historical age-group and serotype-specific IPD incidence was obtained from three PCV10 settings (Finland, Netherlands, and Colombia) and four PCV13 settings (United Kingdom, United States, Quebec, and Ontario). Equations were fitted to longitudinal changes in incidence for each age group, serotype, and country/province over time periods when a serotype was covered or not covered by infant vaccination. We forecasted population impact of PCV13 and PCV10 and report results among infants (ages <2 years) and elderly (65+ years) over 5-years post-vaccine introduction in each setting.
RESULTS: Based on forecasted impact over 5 years post-vaccine introduction, PCV13 was estimated to have greater average overall IPD incidence reduction than PCV10 in infants and the elderly, primarily due to reductions in serotypes 3 and 19A (Table). Both vaccines largely eradicated disease from common PCV10 serotypes. Increases in non-vaccine-type disease greatly varied by setting.
CONCLUSIONS: Forecasting IPD incidence using real-world impact is an intuitive method to illustrate benefits of PCV13 and PCV10 by identifying age- and serotype-specific trends that inherently capture direct and indirect effects of vaccination.
