Retrospective Study And Prediction Of The COVID-19 Outbreak

In the early stages of the COVID-19 outbreak,many countries implemented nonpharmaceutical interventions to control the spread of the disease.Quarantine measures were widely used among these NPIs and were implemented through stay-at-home and shelter-inplace orders.Understanding the effectiveness of quarantine measures can inform decisionmaking and control planning during the ongoing COVID-19 pandemic and future disease outbreaks.This paper mainly reviews the early stages of the COVID-19 outbreak and conducts a series of predictive studies on the implementation of quarantine measures.Mathematical modeling of infectious diseases is a tool for studying the mechanisms of disease transmission,predicting the progress of infectious diseases and evaluating strategies for controlling epidemics.In this study,we develop a susceptible-exposed-infected-removed(SEIR)-type model with a component of quarantine and couple this disease transmission model with the ensemble adjustment Kalman filter method.By calibrating the model to case data,we estimate key epidemiological parameters before lockdown in Wuhan,New York,Milan,and London.Then,we further examine the impact of quarantine rates on COVID-19 spread after lockdown using model simulations based on several characteristics.The results indicate that quarantine of susceptible and exposed individuals and unreported infections is necessary to contain the outbreak;however,the quarantine rates of these groups can be reduced by isolating reported cases more quickly.For a single isolation measure,it is difficult to implement and the marginal cost is high,but the marginal benefit is decreasing,so the prevention and control effect of a combination of multiple isolation measures is better.In addition,counterfactual simulations are generated to estimate the effectiveness of quarantine measures.The cumulative confirmed cases could be much higher than reported numbers within 40 days after lockdown in Wuhan,New York,Milan,and London if the quarantine measures for the susceptible,exposed and unreported infected were lifted.This finding underscores the importance of quarantine in the early stages of a pandemic.Finally,this paper performs model fitting of the transmission dynamics within 60 days after lockdown in four areas.The results show that after a period of lockdown,the effective reproductive number fell below 1 in all four areas.