Abstract
In this paper, we evaluate the effect of the state of emergency for the first wave of COVID-19 in Japan, 2020 from the viewpoint of mathematical modelling. In Japan, it was announced during the period of the state of emergency from April 7 to May 25, 2020 that the 80% reduction of the contact rate is needed to control the outbreak. By numerical simulation, we show that the reduction rate seems to have reached up to 86%. Moreover, we estimate the control reproduction number during the period of the state of emergency as (95%CI, 0.34–0.39), and show that the effective reproduction number after the lifting of the state of emergency could be greater than 1. This result suggests us that the second wave of COVID-19 in Japan could possibly occur if any effective intervention will not be taken again.
Highlights
The first case of novel coronavirus disease 2019 (COVID-19) was identified in Wuhan City, Hubei Province of China on December 31, 2019 (WHO, 2020, Situation report 1)
We estimate the control reproduction number R c during the period of the state of emergency as R c 1⁄4 0:36 (95%CI, 0.34e0.39), and show that the effective reproduction number R e after the lifting of the state of emergency could be greater than 1. This result suggests us that the second wave of COVID-19 in Japan could possibly occur if any effective intervention will not be taken again
R c denotes the control reproduction number (Inaba, 2017, Section 5.5.3), which is given by R c 1⁄4 k* R 0 z0:36 (95%CI, 0.34e0.39). This result suggests us that the state of emergency in Japan for the first wave of COVID-19 resulted in ð1 k* Þ 100 1⁄4 86% reduction of the contact rate
Summary
The first case of novel coronavirus disease 2019 (COVID-19) was identified in Wuhan City, Hubei Province of China on December 31, 2019 (WHO, 2020, Situation report 1). The first case of COVID-19 in Japan was identified on January 15, 2020 (WHO, 2020, Situation report 1). The increasement of the daily number of newly reported cases was observed in late February, and the early intervention such as school closure started from the beginning of March (The Japan Times, 2020). The serious exponential growth of the daily number of newly reported cases started from late March, and the Japanese government declared a state of emergency on April 7, 2020 The daily number of newly reported cases tended to decrease, and the state of emergency was lifted on May 25, 2020 (Kyodo News, 2020). As of June 30, 2020, the daily number of newly reported cases in Japan is kept in a low level (see Fig. 1)
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