Forecasting invasive pneumococcal disease trends after the introduction of 13-valent pneumococcal conjugate vaccine in the United States, 2010-2020

Introduction: Pneumococcal vaccines are highly effective at preventing invasive pneumococcal disease (IPD), a leading cause of global morbidity. Because pneumococcal vaccines can be expensive, it is useful to estimate what impact might be expected from their introduction. Our objective was to develop a statistical model that could predict rates of IPD following introduction of 13-valent pneumococcal conjugate vaccine (PCV13) in the U.S. Methods: We used active surveillance data to design and validate a Poisson model forecasting the reductions in IPD observed after U.S. introduction of 7-valent pneumococcal conjugate vaccine (PCV7) in 2000. We used this model to forecast rates of IPD from 2010 to 2020 in the presence of PCV13. Because increases in non-PCV7-type IPD were evident following PCV7 introduction, we evaluated varying levels of increase in non-PCV13-type IPD ("serotype replacement") by sensitivity analyses. Results: A total of 43,507 cases of IPD were identified during 1998-2009; cases from this period were used to develop the model, which accurately predicted indirect effects of PCV7 in adults, as well as serotype replacement. Assuming that PCV13 provides similar protection against PCV13 serotypes as PCV7 did against PCV7 serotypes, the base-case model predicted approximately 168,000 cases of IPD prevented from 2011 to 2020. When serotype replacement was varied in sensitivity analyses from 0 to levels comparable to that seen with serotype 19A (the most common replacement serotype since PCV7 was introduced), the model predicted 167,000-170,000 cases prevented. The base-case model predicted rates of IPD in children under five years of age decreasing from 21.9 to 9.3 cases per 100,000 population. Conclusions: This model provides a "benchmark" for assessing progress in the prevention of IPD in the years after PCV13 introduction. The amount of serotype replacement is unlikely to greatly affect the overall number of cases prevented by PCV13. Published by Elsevier Ltd.