Estimating the historical impact of outbreak response immunization programs across 210 outbreaks in LMICs

BackgroundOutbreaks of vaccine-preventable diseases continue to occur in low- and middle-income countries (LMICs), requiring outbreak response immunization (ORI) programs for containment. To inform future investment decisions, this study aimed to estimate the cases, deaths, disability-adjusted life years (DALYs), and societal economic costs averted by past ORI programs. Outbreaks of measles, Ebola, yellow fever, cholera, and meningococcal meningitis in LMICs between 2000-2023 were considered. Methods210 outbreaks (51 measles, 40 cholera, 88 yellow fever, 24 meningitis, 7 Ebola) were identified with sufficient data for analysis. Agent-based models were calibrated for each disease such that after controlling for baseline vaccine coverage, ORI initiation time, speed of vaccine delivery, environmental variables, or endemic prevalence of the disease, observed outbreaks were within the distribution of simulated outbreaks. A status-quo and no ORI scenario were compared for each outbreak. FindingsAcross 210 outbreaks, ORI programs are estimated to have averted 5{middle dot}81M [95% uncertainty interval 5{middle dot}75M-5{middle dot}87M] cases (4{middle dot}01M measles, 283K cholera, 1{middle dot}50M yellow fever, 21{middle dot}3K meningitis, 820 Ebola), 327K [317K-338K] deaths (20.0K measles, 5215 cholera, 300K yellow fever, 1599 meningitis, 381 Ebola), 14{middle dot}6M [14{middle dot}1M-15{middle dot}1M] DALYs (1{middle dot}27M measles, 220K cholera, 13{middle dot}0M yellow fever, 113K meningitis, 16{middle dot}6K Ebola), and US$31{middle dot}7B [29{middle dot}0B-34{middle dot}9B] (US$710M measles, US$156M cholera, US$30{middle dot}7B yellow fever, US$97{middle dot}6M meningitis, US$6{middle dot}72M Ebola) in societal economic costs. In general, the more rapidly the ORI was initiated the greater the impact. InterpretationORI programs are critical for reducing the health and economic impacts of outbreaks of vaccine-preventable diseases. FundingGavi,the Vaccine Alliance.