Background Seasonal influenza presents a persistent threat to global health, with the elderly (65 + years) facing disproportionate risks of severe clinical outcomes. While the World Health Organization advocates for targeted immunization, the epidemiological impact of varying vaccination schedules remains a critical area for quantitative evaluation. This study investigates how the prioritization and temporal shifting of vaccine administration influence disease burden within the demographic context of Korea. Method We constructed an age-structured compartment model across four demographic groups (G1:0–14, G2:15–49, G3:50–64, and G4: 65+) using 2023–2024 seasonal influenza data in Korea. Among the various scenarios evaluated, we specifically performed an analysis by advancing the vaccination start date for the elderly group (G4) by up to two weeks to evaluate its comparative effectiveness against the baseline Korean National Immunization Program (KNIP). Furthermore, to quantify parameter uncertainty and assess the robustness of our model, we performed bootstrapping and partial rank correlation coefficient (PRCC) analyses. Results Our analysis reveals that, under the baseline vaccination strategy, the highest infection rates occur in the G1 age group, while early vaccination of the G4 group is found to be effective in reducing hospitalizations and deaths. Specifically, scenarios prioritizing early vaccination for the elderly (G4) with different immune states were associated with a 34.2% reduction in cumulative cases (range: 11.5–53.9%) and a 39.1% decrease in peak infection levels (range: 12.3–60.4%) compared to the baseline. Sensitivity analysis using PRCC showed that the symptomatic infectious period and G4 transmission parameters were identified as the primary drivers of cases and deaths. Conclusion These findings suggest that targeted, timely vaccination of the elderly (65 + years) can contribute to mitigating the overall epidemic burden and alleviating periods of high hospital demand. Our simulation results indicate that age-specific strategies, particularly those accelerating vaccination for the elderly, offer a valuable quantitative framework for reducing the public health impact of seasonal influenza. While these outcomes are subject to model-specific assumptions, they provide a reasonable basis for further refining immunization programs within structured epidemic interventions.
Lee et al. (Mon,) studied this question.