Validation of a Novel Forecasting Method for Estimating the Impact of Switching Pneumococcal Conjugate Programs: Evidence from Belgium

INTRODUCTION: Since 2010, 10-valent (PCV10) and 13-valent pneumococcal conjugate vaccines (PCV13) have been available as part of infant national immunization programs. Belgium is as one of the few countries that implemented PCV13 (2007–2015), switched to PCV10 (2015–2018) and then switched back to PCV13 (2018–present) after observing increases in disease. We assessed the impacts of both historical and prospective PCV choice in the context of the Belgian health care system and used this experience to validate previously developed economic models. METHODS: Using historical incidence (2007–2018) of pneumococcal disease for Belgian children aged < 16 years, observed invasive pneumococcal disease (IPD) trends from surveillance data were used to estimate future disease in a given PCV13- or PCV10-based program. We compared observed incidence data with two modeled scenarios: (1) the 2015 switch to PCV10 and (2) a hypothetical continuation of PCV13 in 2015. Finally, we explored the potential impact of PCV choice from 2019 to 2023 by comparing three scenarios: (3) continued use of PCV10; (4) a switch back to PCV13; (5) a hypothetical scenario in which Belgium never switched from PCV13. RESULTS: Model predictions underestimated observed data from 2015 to 2018 by 100 IPD cases among ages < 16 years. Comparing observed data with scenario 2 suggests that PCV13 would have prevented 105 IPD cases from 2015 to 2018 compared with PCV10. Switching to PCV13 in 2019 would avert 625 IPD cases through 2023 compared with continuing PCV10. Scenario never switching from PCV13 would have resulted in a reduction of 204 cases from 2016 to 2023 compared with switching to PCV10 and switching back to PCV13. CONCLUSION: The findings from this study suggest that previously published modeling results of PCV13 versus PCV10 in other countries may have underestimated the benefit of PCV13. These results highlight the importance of continually protecting against vaccine-preventable pneumococcal serotypes. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40121-021-00485-9.