Costs of influenza-associated healthcare: an umbrella review and meta-regression analysis

Abstract Background Estimates of the healthcare costs associated with influenza treatment are essential for cost-effectiveness analyses that inform preventative and treatment strategies such as vaccination and non-pharmaceutical interventions. Existing evidence varies across treatment settings, age groups, and countries and there is little data from low- and middle-income settings. Methods We conducted an umbrella review of systematic reviews and meta-analyses reporting direct admitted and non-admitted hospitalisation costs of seasonal influenza treatment in children, adults, and older people. We supplemented an evidence gap with a systematised review of studies reporting adult non-admitted treatment costs. Costs were extracted and adjusted to 2023 USD. We fitted a Bayesian mixed-effects model to estimate influenza treatment costs using national economic indicators, age group, and treatment setting as a priori predictors. We predicted admitted and non-admitted treatment costs for children, adults, and older people in 195 countries and territories. Results Seven reviews were included in the umbrella review, supplemented by 17 primary studies for adult non-admitted care. Extracted data points most frequently described admitted treatment costs and came from high-income countries. The best-fitting model used healthcare expenditure per capita to predict treatment costs, with country-level random effects. Estimated costs increased with healthcare expenditure per capita, were higher for admitted than non-admitted care, and were highest for adults and lowest for children. Conclusions This study provides novel estimates of influenza-associated healthcare costs across age groups and treatment settings by synthesising the available global evidence. By extrapolating to settings without data, our estimates can inform future economic evaluation studies of influenza interventions worldwide.