Proposal of an SEIR Model Considering Inter-population Transfers and Vaccine Availability in Large Populations

This study proposes an infectious disease model incorporating person-trip data and adopts an extended SEIR framework based on the classical SIR model. The analysis specifically targets the spread of the Omicron variant of COVID-19, which proliferated across Japan in the early months of 2022. Following the construction of a SEIR-based epidemiological model, a single infectious region is segmented into four distinct groups to simulate diverse transmission dynamics through person-trip movements. Using empirical records of infection cases and commuter flows in Saitama, Tokyo, Kanagawa, and Chiba prefectures from January to April 2022, the model estimates key parameter values, including infection rate, recovery rate, and mobility rate. Additionally, vaccine efficacy parameters released by the Ministry of Health, Labour and Welfare are incorporated into the simulation. Based on the estimated parameters, the study investigates the potential for mitigating the spread of infection. The model’s validity is then assessed by comparing the simulated data of new infections with actual epidemiological data from the aforementioned four prefectures used in the parameter estimation. Furthermore, the study explores various scenarios by altering the parameters related to human mobility and vaccine efficacy to evaluate which preventive measure—mobility restriction or immunity acquisition through vaccination—more effectively curtails the spread of infection.