疫学データから考えるCOVID-19対策の指針

COVID-19 in Japan: Insights from the Epidemiological Data

日本は新型コロナウイルス感染症（COVID-19）のPCR検査率が低いことが批判されているが，PCR検査率は封じ込め成功にも死亡率抑制にも関係はなく，封じ込め成功の主因はソーシャル・ディスタンシングと考えられる。日本を含む東アジアの死亡率の低さは感染が広がっていないことも一因である。日本は世界一の高齢化の中，高齢者選択性の極めて高いCOVID-19の死者の抑制に成功している。今後の方策として弱毒化も期待され，日本では東京が先行して軽症化している可能性がある。

Abstract

The coronavirus disease 2019 (COVID-19) pandemic is a worldwide peril. The PCR tests are widely used to detect infections. However, multiple regression analysis revealed no correlation between the examination rate among population (ER) and the success of containment, which is achieved by social distancing. ER and fatality rate were even positively correlated. Japan has been criticized for its very low ER, but it achieved better containment than other major countries with much higher ER on 29 May. The estimation of the true infection rate (TIR) among population revealed that the low fatality rate in Japan and other Asian countries is partly due to low TIR. Fatality of COVID-19 is highly accentuated in aged persons. Despite having the highest aging rate in the world, the fatality rate in Japan is relatively low. The corrected fatality rate of Japan is the second-lowest among the G20 countries. Mimicking the attenuation of viral virulence due to natural selection would be a promising strategy to overcome pandemic. The prevention of in-hospital transmission, especially from severe cases, would be the key to achieve this. Attenuation of the viral virulence in the second wave is evident in many European countries, and also in Tokyo.