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(proposed a new compartment model for COVID-19, which treats pre-symptomatic and asymptomatic patients as compartments. It is shown that the fraction of untraceable patients and the ratio between the number of patients at large and the daily new cases can be estimated.)
(A simple method is devised to estimate the onset rate of COVID-19 from the proportion of untraceable patients tested positive.)
(With Reiji Suda: A simple method to estimate the rate of change of the number of infected individuals is proposed. The infection statuses of 190 countries around the world are analyzed and classified into 9 states.)
(When the rate of change fluctuates according to the number of infected individuals, it is theoretically shown that the epidemic curve shows oscillation and that convergence is possible only when a zero-corona state is realized.)
(It is theoretically shown that the wavy infection curve is the result of fluctuation in policy and attitude of people.)
(Exact solution for the SIQR model is presented. It is shown that the quarantine measure is effective for controlling COVID-19. A theoretical frame work to find an optimum measure ia proposed.)
(The SIQR model is proposed for COVID-19, and it is shown that the quarantine measure is important to contol the epidemic.)
"Effects of superspreaders in spread of epidemic"（Physica A374, 843-852 (2007))
(With R. Fujie：On the basis of an agent based model, the superspreaders for SARS are shown to be patients who have a long infection range.)