Economic analysis of adjuvanted trivalent influenza vaccine for older adults in the Korean National Immunization Program

BackgroundSeasonal influenza causes substantial morbidity and mortality among older adults in South Korea despite high vaccination coverage. The MF59-adjuvanted trivalent influenza vaccine (aTIV) has shown superior immunogenicity in older populations, but its economic value within the Korean National Immunization Program (NIP) has not been evaluated using a dynamic transmission model that captures indirect protection. This study evaluated the budget impact of introducing aTIV into the Korean NIP for adults aged ≥65 years.MethodsWe developed an age-structured dynamic compartmental model to simulate seasonal influenza transmission in South Korea, allowing estimation of both direct and indirect protection effects. From the healthcare payer perspective and over a single influenza season, we performed a budget impact analysis complemented by a cost–benefit comparison of avoided medical costs against incremental vaccination expenditures. Two aTIV strategies were compared against standard quadrivalent influenza vaccine (QIV) within the NIP framework: Strategy I (aTIV for adults aged ≥75 years) and Strategy II (aTIV for all adults aged ≥65 years). Deterministic one-way sensitivity analyses examined relative vaccine effectiveness (rVE) of aTIV versus QIV across 5–30% and seasonal attack rate across ±20% of the 8.0% baseline, and a break-even analysis identified the rVE threshold at which incremental costs equal avoided treatment costs. A probabilistic sensitivity analysis was also conducted to quantify joint parameter uncertainty.ResultsAt baseline (rVE 25%, attack rate 8.0%), Strategy I required $24.6 million in additional vaccine investment, with 52% offset by treatment savings, yielding a net budget impact of $11.7 million (+0.9% of total influenza-related healthcare expenditure). Strategy II required $54.4 million in additional costs with 57% offset ($31.2 million in savings), resulting in a net impact of $23.2 million (+1.8%). Strategy II prevented 535 deaths and over 15,000 hospitalizations—2.2-fold greater than Strategy I. The incremental cost of aTIV decreased with increasing transmission intensity, approaching cost neutrality during severe epidemic seasons. The break-even rVE at which aTIV becomes cost-saving was 44%, above central meta-analytic estimates (10–25%) but potentially attainable in severe seasons or specific subpopulations.ConclusionIntroduction of aTIV into the Korean NIP is budget-feasible with substantial health benefits, requiring only a 0.9–1.8% increase in total influenza-related healthcare expenditure. At current rVE estimates (≤30%), aTIV does not achieve cost savings, but the additional fiscal burden remains modest. Strategy II offers superior health outcome value and is preferred when budget permits, while Strategy I provides a fiscally conservative entry point. The value proposition of aTIV is most favorable during severe influenza seasons.