Effectiveness of Social Measures Against COVID-19 Outbreaks in Japanese Several Regions Analyzed by System Dynamic Modeling

In Japan's response to coronavirus disease 2019 (COVID-19), virus testing was limited to symptomatic patients due to limited testing capacity. This made it difficult to get a complete picture of the infection, and it is still making it difficult to assess the appropriateness of various countermeasures. Therefore, we considered the use of system dynamic modeling to capture the whole picture of the infection. A stock-flow model was employed to describe the dynamics of infected population. Three regions in Japan, Tokyo, Osaka, and Hokkaido, where a considerably large number of patients were reported, were studied. The infection model was assumed to have a region-specific transmission rate in the initial phase of the outbreak; subsequently, the transmission rate was reduced in a data-driven manner based on the actual number of patients in the course of the intervention. Model-based simulations have shown that quarantine of all inbound travelers at airports has a certain effect on reducing the total number of patients. The government's intervention to restrict people from going out during the state of emergency was found to be effective in reducing transmission. The causal loop model was constructed, and how societal factors contribute to infection control was studied. The only element that worked against transmission was the intervention by national and local governments. At present, government intervention is considered essential in the early stages of the outbreak of new infectious diseases. It is necessary to create resistance to infectious diseases in society, an issue that needs to be addressed in the future