Several Types Of Real-world Scenarios Modeling And Simulation Of COVID-19 Transmission

COVID-19,which broke out at the end of 2019,is an emerging infectious disease with the widest range of influence and the largest number of infected individuals since the beginning of the 21 st century.It has an unprecedented impact on global public health and people’s lives,and has caused inestimable losses to social and economic development.Dynamic models are useful tools to study emerging infectious disease.Since the outbreak of COVID-19,domestic and foreign scholars have established a variety of dynamic models to simulate the transmission of COVID-19,depict the internal transmission mechanism,and excavate the key factors to control the transmission of the infectious diseases,providing scientific theoretical guidance and quantitative basis for the prevention and control of infectious diseases.Taking COVID-19 as the research background,this thesis mainly studies the epidemic prevention and control issues focused on four real-world scenarios: Wuhan and Mainland China(outside Wuhan)in the early epidemic phase,Yangzhou City in the mid-epidemic phase,boarding schools in the mid-epidemic phase,and Neijiang City in the post-epidemic era,and establishes patches coupled network model,multi-group model,multi-path coupled network model,and mean field model,respectively.Through theoretical analysis,the existence of the final size are discussed,and the threshold conditions to distinguish whether the disease is prevalent or not are given.In terms of application,according to different real-world scenarios,the transmission law of COVID-19 in the population is studied,the effectiveness of various intervention measures is evaluated,and the high-risk groups of infectious disease transmission are excavated.The main work includes the following four parts:(1)The study of effectiveness and exit of COVID-19 interventions in the early epidemic phase.Based on COVID-19 transmission and diffusion mechanism,combined with the actual implementation of travel restrictions,tracing and quarantining of close contacts and other intervention measures,establish a coupled network model with Wuhan and Mainland China(outside Wuhan).Theoretically,the dynamic behavior of the established model is analyzed.In addition,combined with the actual data,the least square method is used to estimate the unknown parameters.The model is numerically simulated to evaluate the effectiveness of the interventions.The results show that that it is not possible to control the spread of COVID-19 through travel restrictions or tracing and quarantining of close contacts alone.Furthermore,considering vaccination,if withdraw from the implemented non-pharmaceutical interventions,the protection rate of herd immunity needed for people to return to normal life is 60.63%.(2)The study of impact of contact patterns on the spread of COVID-19 in the mid-epidemic phase.Human-to-human contact plays a key role in the transmission of COVID-19.While,the contact is heterogeneous,which varies with age,household size and time.Based on this,we define two contact patterns: regular contact and random contact.Combined with the heterogeneity of age and household size,a multi-group model for switching between daytime and nighttime is established to describe the transmission process of COVID-19 in the population.The established model is applied to the COVID-19 outbreak in Yangzhou City,China at the end of July 2021.First of all,the expressions of the reproduction number of different age groups and household sizes are given.By comparison,it is find that young and middle-aged adults(aged 18-59)with household size of 6 have the strongest transmission ability.Secondly,the influence of the proportion of the two contact patterns on the transmission of COVID-19 is studied.The result shows that increasing the proportion of random contact is beneficial to the control of the infectious disease in the phase with interventions.At last,taking the final size,the peak value of infected individuals in community and the peak value of quarantine infected individuals and nucleic acid test positive individuals as indicators,we evaluate the impacts of the random contact number,the duration of the free transmission stage and summer vacation on the transmission of the disease.And the reasearch shows that the larger the random contact number and the longer the duration of free transmission stage,the more disadvantageous to the control of the infectious disease.While,the summer vacation is beneficial to the control of the infectious disease.(3)The study of COVID-19 transmission in school in the mid-epidemic phase.The school is highly densely populated and is the key place for COVID-19 prevention and control.Based on the real study and life of teachers and students in a boarding school,a contact network is constructed to depict local contact of individuals,and a multi-path coupled network model is established combined with global contact.Three indexes of outbreak intensity,infection risk index and the disease growth velocity are defined to study the transmission law of COVID-19 in school.Furthermore,by comparing patient zero is a student or a teachers in different grades,it is find that on the whole,students have higher transmission risks than teachers,while lower grade students and teachers have higher transmission risks than higher grade students;then,study the priority contact and global contact,and the results show that priority contact inhibits the transmission of COVID-19,while global contact promotes the transmission of COVID-19 among individuals of different grades;if conditions permit,properly reducing the size of accommodation and class size is beneficial to the control of COVID-19.(4)The study of the transmission trend of COVID-19 in the post-epidemic era.On December 7,2022,with announcing the new 10 measures on COVID-19 prevention and control,China withdrew from the Zero-COVID policy.Since then,COVID-19 massive outbreak in Mainland China for the first time.Based on this background,a classical well-mixed model is established to study the infection situation during the first massive outbreak in Neijiang City,Sichuan Province,China and to evaluate the effectiveness of protective measures taken by susceptible individuals.The results show that the number of infected individuals reaches 74.8%of the total population on January 1,2023.And,if the effective protection rate of susceptible individuals decreases by 0.05,the proportion of cumulative infected cases will increase by20.45%;if the effective protection rate of susceptible individuals increases by 0.05,the proportion of cumulative infected cases will decrease by 17.63%.