Estimation of reproduction numbers of COVID-19 in typical countries and epidemic trends under different prevention and control scenarios

The coronavirus disease 2019(COVID-19)has become a life-threatening pandemic.The epidemic trends in different countries vary considerably due to different policy-making and resources mobilization.We calculated basic reproduction number(R0)and the time-varying estimate of the effective reproductive number(Rt)of COVID-19 by using the maximum likelihood method and the sequential Bayesian method,respectively.European and North American countries possessed higher (R0)and unsteady Rt fluctuations,whereas some heavily affected Asian countries showed relatively low (R0)and declining Rt now.The numbers of patients in Africa and Latin America are still low,but the potential risk of huge outbreaks cannot be ignored.Three scenarios were then simulated,generating distinct outcomes by using SEIR(susceptible,exposed,infectious,and removed)model.First,evidence-based prompt responses yield lower transmission rate followed by decreasing Rt.Second,implementation of effective control policies at a relatively late stage,in spite of huge casualties at early phase,can still achieve containment and mitigation.Third,wisely taking advantage of the time-window for developing countries in Africa and Latin America to adopt adequate measures can save more people’s life.Our mathematical modeling provides evidence for international communities to develop sound design of containment and mitigation policies for COVID-19.

Phase-and epidemic region-adjusted estimation of the number of coronavirus disease 2019 cases in China

The outbreak of the coronavirus disease 2019 in China was first reported in Wuhan in December 2019 and gradually spread to other areas in China.After implementation of prevention and control measures,the estimation of the epidemic trend is needed.A phase-and region-adjusted SEIR model was applied for modeling and predicting the number of cases in Wuhan,Hubei Province and regions outside Hubei Province in China.The estimated number of infections could reach its peak in late February 2020 in Wuhan and Hubei Province,which is 55303–84520 and 83944–129312,respectively,while the epidemic peaks in regions outside Hubei Province in China could appear on February 13,2020 with the estimated 13035–19108 cases.According to the estimation,the outbreak would abate in March and April all over China.Current estimation provided evidence for planned work resumption under stringent prevention and control in China to further support the fight against the epidemic.Nevertheless,there is still possibility of the second outbreak brought by the work resumption and population migration,especially from Hubei Province and high intensity cities outside Hubei Province.Strict prevention and control measures still need to be considered in the regions with high intensity of epidemic and densely-populated cities.