Cost-effectiveness of annual trivalent inactivated influenza vaccine program by age and risk status

Objective: To evaluate the cost-effectiveness of annual trivalent inactivated influenza vaccine (IIV3) under the context of Zhejiang province. Methods: A state transition simulation model was constructed to estimate the health and economic outcomes of IIV3 vaccination program compared to no vaccination for hypothetical cohorts of Zhejiang province stratified by age and risk status. Model input parameters were chosen based on published literatures and expert advices. The analysis used societal perspectives and a one-year time horizon, and permanent outcomes were also included. The primary outcome was the incremental cost-effectiveness ratio (ICER), with expression of US dollars per quality adjusted life years (QALYs) gained. Results: In subgroups not at high risk for influenza-related complications (non-high risk subgroup), ICER ranged from $6 268/QALY (for adults aged 50-64 years) to $11 260/QALY (for children aged from 6 months to 4 years). In subgroups at high risk for influenza-related complications (high risk subgroup), ICER ranged from cost-saving (adults aged ≥65 years) to $5 260/QALY (for children aged from 6 months to 4 years). ICER were most sensitive to changes in probability of influenza illness, cost of hospitalization, and probability of death for adults aged 18-49 years with non-high risk status. Conclusions: ICERs of annual influenza vaccination varied by age and risk status but were less than the Gross Domestic Product (GDP) per capita of Zhejiang province ($17 745 in 2023), which remained cost-effective for all-age and different risk status groups from a societal perspective.