The Deaths Lost in Vaccine Projections: An Examination of the Impact of Vaccination Scenarios on Forecasted Mortality Attributable to Pneumococcal Lower Respiratory Infections

Abstract

Mortality forecasts can be a way to quantify the impact that causes of death may have over a period of time based on current trends. Cause-specific forecasts depend on associated mitigating factors and drivers. The focus for this work was pneumococcal lower respiratory infections (LRI) and the pneumococcal conjugate vaccine (PCV). The Future Health Scenarios team (FHS) at the Institute for Health Metrics and Evaluation (IHME) uses third-dose PCV (PCV3) forecasts as a covariate for mortality attributable to pneumococcal LRI. Variations in PCV3 forecasting methodologies correspondingly impact the projected mortality attributable to pneumococcal LRI. The goal of this study is to determine the degree of variation in mortality between scenarios attributable to non-vaccination status by estimating mortality arising as a consequence of that status.Four vaccination coverage forecasts were made, two to serve as the outer bounds of vaccination coverage, and two to represent the scenarios being compared. These forecasts were then used as the basis of forecasts of mortality attributable to pneumococcal LRI and, in turn, the variation in mortality between these vaccination scenarios. Once these data were available, comparisons of total difference in mortality, mortality attributable to vaccination, and ratios of those differences and attributable fractions were made to determine the impact of the vaccination forecasts. Findings from the work involved in this paper suggest that differences of 1.6% to 2.4% exist between scenarios produced for this work. This translated to between 85 and 114 thousand deaths globally for the under-5 age group attributable to pneumococcal LRI between the years 2022 and 2050. This variation arose solely due to changes in vaccine forecasting methodology with all other variables and covariates held constant between mortality calculations.