Cost-Effectiveness of Adult Hepatitis A Vaccination Strategies in Korea Under an Aging Susceptibility Profile

Hepatitis A severity increases sharply with age, while Korea is experiencing a cohort shift in which low-seroprevalence adult cohorts are aging into older, higher-fatality age groups. This demographic and immunological transition creates an urgent policy question regarding how adult vaccination should be prioritized under resource constraints.

This study aimed to identify the most cost-effective adult hepatitis A vaccination strategy in Korea by comparing age-targeted vaccination scenarios that account for age-related mortality risk, socioeconomic disease burden, and realistic resource constraints.

We evaluated three adult vaccination scenarios targeting low-seroprevalence age groups: (S1) 20-39 years, (S2) 40-59 years with pre-vaccination antibody testing, and (S3) 20-59 years with antibody testing applied to those aged ≥ 40 years. Using an age-structured dynamic transmission model calibrated to Korean data, we derived dynamically feasible vaccination allocation trajectories under realistic capacity constraints using an optimal control framework and linked these trajectories to long-term transmission-model simulations. We conducted cost-effectiveness analyses based on disability-adjusted life years (DALYs) over a lifetime horizon from both healthcare system and societal perspectives and characterized uncertainty using probabilistic sensitivity analysis (PSA) and cost-effectiveness acceptability curves (CEACs). Robustness was examined using one-way sensitivity analyses.

In the base case (4.5% annual discount rate), vaccination targeting adults aged 40-59 years (S2) consistently yielded the most favorable and robust cost-effectiveness profile under both perspectives, with the lowest incremental cost-effectiveness ratio (ICER). Vaccination of adults aged 20-59 years (S3) achieved the largest reduction in DALYs but required substantially higher incremental costs, resulting in a higher ICER than (S2). The smallest DALY reduction was produced by S1, which was the least efficient strategy. The PSA and CEACs confirmed that S2 remained the preferred option across most willingness-to-pay ranges.

Prioritizing adults aged 40-59 years offers the most balanced and robustly cost-effective strategy for hepatitis A vaccination in Korea, capturing substantial mortality reduction while limiting additional program costs. Broader adult vaccination may be justified when higher budgets or willingness-to-pay thresholds are acceptable, but prioritizing middle-aged adults provides the clearest value for money under epidemiological and economic conditions.