摘要
1.Overview Since its first emergency,COVID-19 has spread to over 200 countries and regions.On 22 April 2020,WHO re-p orted 2,471,136 positive cases confirmed and 169,006 deaths1.While medical data showed that COVID-19 outbreak does not take the first rank of highest death toll pandemic in history,it has shaken the world by bringing the economy to a near-grinding halt.