Health-economic impacts of age- and sex-targeted Lassa fever vaccination in endemic regions of Nigeria, Guinea, Liberia and Sierra Leone: a modelling study

Introduction: Lassa fever is an emerging zoonotic disease endemic to West Africa. Several vaccines aimed at preventing Lassa fever are currently under development, creating a need to assess how best to administer them once licensed for human use. Methods: We developed a mathematical model using a zoonosis risk map and epidemiological data from recent and ongoing cohort studies to predict the health-economic burden of Lassa fever across age and sex groups in endemic regions. We simulated vaccination campaigns targeting different risk groups to estimate the health-economic benefits of various scenarios for Lassa vaccine administration. Threshold vaccine costs (TVCs) were estimated in International dollars (I$ 2023), accounting for healthcare costs, productivity losses and monetised disability-adjusted life-years (DALYs) averted due to vaccination. Results: The most efficient strategy for preventing symptomatic Lassa fever was targeting children aged 2-14, for preventing hospitalisation was targeting adolescents and adults aged 15-49, for preventing death was targeting older adults aged 50+, and for preventing DALYs was targeting women of childbearing age (WCBA) aged 15-49. Under base case assumptions, the highest TVC for a single-dose vaccine was estimated at I$7.39 (95% uncertainty interval (UI): I$4.33-I$11.60) when targeting adolescents and adults, followed by I$6.69 (95%UI: I$4.17-I$9.85) when targeting older adults, I$6.10 (95%UI: I$3.56-I$9.74) when targeting WCBA and I$1.94 (95%UI: I$1.10-I$3.10) when targeting children. Conclusion: These results suggest that the most cost-efficient use of limited doses of Lassa fever vaccine is to target adolescents and adults followed by the elderly.