Forecast of the COVID-19 outbreak and effects of self-restraint in going out in Tokyo, Japan

Background The number of patients of COVID-19 in Tokyo has been increasing gradually through the end of March, 2020. Object Support for policymaking requires forecasting of the entire course and outcome of the outbreak if a self-restraint in going out is not initiated. Moreover, the effects of a self-restraint in going out must be considered when choosing to initiate one. Method: Data of Tokyo patients with symptoms during January 14 – March 28, 2020 were used to formulate a susceptible–infected–recovered (SIR) model using three age classes and to estimate the basic reproduction number (R 0 ). Based on the estimated R 0 , We inferred outbreak outcomes and medical burden if a self-restraint in going out were not enacted. Then we estimate the self-restraint in going out effects. Results Results: suggest R 0 as 2.86, with a 95% confidence interval of [2.73, 2.97]. Exhaustion of medical resources can be expected to occur on April 26 if no self-restraint in going out occurs. If a self-restraint in going out were enacted from April 6, and if more than 60% of trips outside the home were restricted voluntarily, then medical care service could be maintained. Discussion and Conclusion The estimated R 0 was similar to that found from other studies conducted in China and Japan. Results demonstrate that a self-restraint in going out with reasonable cooperation of residents is required to maintain medical care.