Abstract: The worldwide spread of Corona Virus Disease 2019 (COVID-19) since January 2020 makes it challenging for each country to prevent and control the disease.In order to assess how effective a country's policies are in guarding against COVID-19 in the absence of effective vaccines,this paper introduces a new implied social distance index (ISD index) based on an extended vSIR infectious disease model,to each country or region,which can quantify the effects of national quarantine policies effectively.Firstly,this research indicates ISD index can conveniently measure the effectiveness of each country/region's prevention and control policies in real time and can reflect the dynamic change in the delayed control of virus transmission and spiking and reducing patterns temporally.Secondly,since social quarantine may impact normal social production activities adversely,we hope to find out how various policies affect economic development under the epidemic by using ISD index,so as to provide constructive opinions on the adjustment of follow-up policies and the economic recovery in the post-epidemic era.Therefore,in this paper,we use monthly manufacturing Purchasing Managers' Index (PMI) as a proxy to measure economic impact and use Pearl's causal model to verify the relationship between ISD index and PMI.On average,when an economy implements a whole society social isolation policy,there is an opposite relationship between degree of social distancing and level of economic cooling down.That is,the larger the ISD index is,the better the Covid-19 spread gets controlled and the more seriously the social and economic activities get affected.When an economy implements precise social isolation policies,such policies barely have impact on the economic growth.

Key words: virus outbreak, SIR model, social distancing, pandemic control, economic growth