The SIQR model is exploited to analyze the outbreak of COVID-19 in Japan where the number of the daily confirmed new cases is explicitly treated as an observable. It is assumed that the society consists of four compartments; susceptible individuals (S), infected individuals at large (I), quarantined patients (Q) and recovered individuals (R), and the time evolution of the pandemic is described by a set of ordinary differential equations. It is shown that the quarantine rate can be determined from the time dependence of the daily confirmed new cases, from which the number of infected individuals can be estimated. The infection rate and quarantine rate are determined for the period from mid-February to mid-April in Japan and transmission characteristics of the initial stages of the outbreak in Japan are analyzed in connection with the policies employed by the government. The effectiveness of different measures is discussed for controlling the outbreak and it is shown that identifying patients through PCR (Polymerase Chain Reaction) testing and isolating them in a quarantine is more effective than lockdown measures aimed at inhibiting social interactions of the general population. An effective reproduction number for infected individuals at large is introduced which is appropriate to epidemics controlled by quarantine measures.

中文翻译：

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利用 SIQR 模型分析日本 COVID-19 疫情。

利用 SIQR 模型来分析日本 COVID-19 的爆发，其中每日确诊的新病例数被明确视为可观测值。假设社会由四个部分组成；易感个体（S）、在逃感染个体（I）、隔离患者（Q）和康复个体（R），大流行的时间演变由一组常微分方程描述。结果表明，可以根据每日新增确诊病例的时间依赖性来确定隔离率，并据此估计感染人数。确定日本2月中旬至4月中旬的感染率和隔离率，并结合政府采取的政策分析日本疫情爆发初期的传播特征。讨论了控制疫情的不同措施的有效性，结果表明，通过 PCR（聚合酶链式反应）检测识别患者并将其隔离隔离比旨在抑制普通人群社交互动的封锁措施更有效。引入了适用于隔离措施控制的流行病的大范围感染者的有效繁殖数。