Research On COVID-19 Epidemic Situation Based On SEIR Model

COVID-19,which broke out in late 2019,is still endemic around the world.Novel coronavirus is similar to earlier SARS and MERS.It can also cause respiratory infectious diseases and has the characteristics of strong transmission power.However,2019-nCoV is significantly less lethal than SARS and MERS,and novel coronavirus is highly variable and may cause asymptomatic infections.These differences have kept the 2019-nCoV alive.As a result of the emergence of the 2019-nCoV pandemic,the lives of people around the world have changed dramatically.It has put people’s lives and property under constant threat.Therefore,the establishment of infectious disease dynamics model suitable for the current epidemic development stage can reflect the trend of epidemic change and predict the trend of epidemic,and provide theoretical support for epidemic prevention and control in the future.This is of practical importance in restoring all aspects of our lives and emerging from the 2019-nCoV cloud as soon as possible.This study,based on the SEIR model,-studies the development of COVID-19 in Xi’an and the United Kingdom in the same period.Firstly,based on the SEIR model,the compartments and parameters of the model are modified to obtain seven compartments including Susceptible(S)-Exposed(E)-Infected(I)-Isolated Susceptible(Sq)-Isolated Exposed(Eq)-Isolated Infected(Iq)-Recovered(R).Secondly,according to the implementation of specific epidemic prevention and control measures in Xi ’an,the model fitting process is divided into three periods.Fixed parameters are adopted in the first two periods,and according to the model fitting situation the cure rate is set as time-varying parameter in the third period,which greatly improves the fitting accuracy of the model after adjustment.The optimal parameters are obtained by the trust region algorithm,which is the optimization algorithm of nonlinear least square estimation,and then the model is fitted and solved by the fourth order Runge-Kutta method.Furthermore,the model is evaluated from two aspects:From the aspect of model fitting effect,the mean absolute percentage error MAPE is defective,so the mean absolute percentage error MAPE and root mean square error RMSE are combined to evaluate the fitting effect of the model.The results show that the evaluation indexes of isolated infected patients(Iq)perform well,while the results of infected patients(I)and recovered patients(R)have some errors.But the errors are within acceptable range;From the aspect of practical meaning,the parameters of the three stages have obvious practical meaning,which further shows that the proposed model is in line with actual meaning.Finally,the epidemic prevention measures taken in Xi’an are discussed by changing the model parameters,and the conclusion is that the current measures adopted in China can effectively prevent the further development of the epidemic.The prevention and control measures adopted by many countries are quite different from those adopted by China,and the magnitude of COVID-19 case data in some regions is relatively large.Therefore,the epidemic situation in the UK at the same period is selected for research and discussion.Firstly,the SEIRD model is established after the compartments and parameters are modified based on the SEIR model.The parameters of the model are adjusted in the empirical analysis,and then the cure rate and mortality are taken as time-varying parameters.The evaluation index MAPE of the model is 3.07%,and the optimal parameters obtained by the least square estimation have obvious actual meaning.Secondly,a short time prediction is made for the model.The prediction results of the model have some deviation,but the prediction result is consistent with the actual epidemic development trend,indicating that the prediction result has certain reference value.Furthermore,the SEIRD model and SIRD model with fixed parameters are compared with the epidemic data of the UK from December 4,2021 to January 10,2022.The results show that the MAPE of the former is 3.45%,while the MAPE of the latter is 10.73%,which indicates that the fitting effect of SEIRD model is better than that of SIRD model.Finally,the development of the epidemic is discussed by changing the model parameters,and the results show that isolation and personal protection measures can largely control the increase in the number of infections.