Quantifying relative health impact across Gavi, the Vaccine Alliance's portfolio in 117 countries at the subregional level: a modelling study

Abstract

BACKGROUND: Estimates of vaccine impact have typically been used to quantify the effects of, and inform, immunisation strategies. Given the growing resource constraints on health systems worldwide, robust estimates of vaccine impact that allow comparison across different vaccines are now more crucial for decision making than ever. Building on previous modelling studies, we aimed to estimate vaccine impact ratios for an expanded portfolio of Gavi, the Vaccine Alliance-supported vaccination programmes against 14 vaccine-preventable diseases across 117 low-income and middle-income countries using multiple models. METHODS: In this modelling study, we have presented Vaccine Impact Modelling Consortium estimates of vaccine impact ratios, defined as deaths or disability-adjusted life-years averted per 1000 vaccinations, for the Gavi portfolio of vaccines. Modelling groups used standardised inputs for demographic data and vaccination coverage assumptions, including a no-vaccination counterfactual, and accounted for structural, parameter, and stochastic uncertainty to produce burden estimates. These estimates were then compared to calculate vaccine impact ratios, disaggregated by immunisation activity type and geographical subregions for vaccinations given between 2000 and 2030 (or 2000 and 2040 for cholera). FINDINGS: Overall, we observed human papillomavirus (11·24 [95% uncertainty interval 10·88-11·64]) and measles (6·09 [4·90-7·07])vaccines averting a higher number of deaths per 1000 vaccinations than others. For other vaccines, the impact ratios varied across subregions and activity types. Due to parameter, structural, and stochastic uncertainty, the ranges of these ratios often overlap. INTERPRETATION: Decisions around which vaccines to use are increasingly important in the context of Gavi's country vaccine budgets. Robust metrics that allow comparison between vaccines are thus essential to inform discussions. The vaccine impact ratios presented in this study can be used to complement other evidence to support effective planning and prioritisation in national immunisation programmes. FUNDING: Gavi, the Vaccine Alliance, Gates Foundation, and Wellcome Trust.