Effect of emergency declaration for the COVID-19 outbreak in Tokyo, Japan in the first two weeks

Background Japan’s Prime Minister Abe declared an emergency to control the COVID-19 outbreak on April 7, 2020. He asked almost half of the population of Japan to reduce their personal contacts by 70–80%. Object This study estimates the effectiveness of that emergency declaration. Method: We applied a simple susceptible–infected–recovery model to data of patients with symptoms in Tokyo, Japan for January 14 – April 21 as of April 22. We estimate the reproduction number in four periods: R 0 before voluntary event cancellation and school closure (VECSC) which was introduced since February 27 to March 19, R v during the VECSC, R a after VECSC, and R e after the emergency declaration. Results Results: suggest that the value of R 0 was estimated as 1.267; its range was [1.214, 1.341]. However, R v was estimated as 2.360 [1.844, 2.623]. R a was estimated as 2.307 [2.035, 2.794] and R e was 0.462 [0.347, 0.514]. Discussion and Concussion One must be reminded that these results reflect only those at two weeks after the emergency declaration. The reproduction number probably changed thereafter continuously.