Medical care cost dynamics during COVID-19 pandemic: financial implications for Japanese health insurance system

While the COVID-19 pandemic globally affected healthcare utilization, economic impacts on medical care costs and insurance finances remain underexamined. In Japan, where aging-related medical care cost increases are becoming serious concerns, quantitative evaluation is crucial for sustainable health insurance system design. This study analyzed the economic impact of COVID-19 on medical care expenditure and utilization rates for non–COVID-19 diseases among the working-age population in Japan. We analyzed continuously enrolled workers aged 20–74 using medical claims data from the Japan Health Insurance Association (May 2015-December 2021). For calculating monthly medical care expenditure, we employed a two-part model of utilization rate and incurred medical care expenditure. Disease-specific allocation for incurred medical care expenditure used Bayesian-based decomposition methods. Using interrupted time series analysis with March 2020 as intervention point, we estimated pandemic impacts on medical care expenditure and utilization rates, stratified by sex, disease group, and type of care. Analysis included 5,826,233 men and 2,971,364 women. During the first state of emergency (April-May 2020), significant decreases in monthly medical care expenditure and utilization rates occurred across most disease groups. For neoplasms, from the second state of emergency (January-March 2021) onward, medical care expenditure increased persistently in outpatient care in both sexes and in inpatient care in men, exceeding utilization rate increases. For diseases of the circulatory system, notable medical care expenditure increases (up to ~ 40%) occurred in men’s inpatient care from the second state of emergency onward, while utilization rate increases remained below 25%, showing differences between the two outcomes. For diseases of the respiratory system, decreases in medical care expenditure persisted throughout the entire period in outpatient care, averaging ~ 18% (men) and ~ 27% (women) monthly. For endocrine, nutritional and metabolic diseases, pandemic impacts were minimal compared to other groups. The impact of the pandemic on medical care expenditure and utilization rates varied substantially by sex, disease group, and type of care. These findings provide important policy implications for ensuring the sustainability of health insurance finances during future infectious disease crises and for establishing healthcare delivery systems that consider economic efficiency.