扬州城新冠疫情清零防控模式的建模和分析

Modeling and Analysis of Zero-COVID Policy of Trace-test-quarantine for Its Control in Yangzhou City

新冠德尔塔病毒通过境外输入在广州、南京、扬州等地区局部散发.在中国政府强有力的监管防控政策和全市人民的密切配合下,通过“追踪-检测-隔离”清零防控模式,找出“零号病人”,确定传染链,进行全员核酸检测精准筛查密切接触者,并及时采取不同等级的隔离措施,阻断传染链,多地小规模的聚集性疫情在近一个月内能够得以控制.本文以扬州市COVID-19疫情防控为研究对象,通过区分社区和集中隔离点的感染者,建立了具有隔离和大规模检测的传染病模型,研究当前清零模式成功的机制,并利用相关参数模拟了扬州的抗疫成功的过程.利用新模型,我们比较分析“躺平”模式,消极模式以及推迟当前清零政策等,研究了多种情形下的疫情发展趋势及其影响.

In 2021,like many other places of the world,some China cities including Guangzhou,Nanjing,Yangzhou experienced outbreaks of delta strain of SARS-CoV-2.Under the Zero-COVID national control strategy and adherence of the society,the small-scale epidemic in many places have been well under control in nearly a month.The Zero-COVID policy employs the trace-test-quarantine procedure,that is,finding the Patient Zero,identifying the infection chain of contacts,conducting the nucleic acid test for all to accurately screen close contacts,and followed by different levels of isolation to block the infection chain.In this paper,we build a new model to mimic the Zero-COVID strategy applied in Yangzhou,a Chinese city with a population of nearly 1.7 million.The novel dynamic model with timedelays describing isolation and large-scale detection is established by distinguishing infected persons in communities and centralized isolation areas.Using numerical simulations,we compare the scenarios under different control modes and levels.Our simulation shows that the less aggressive mitigation mode could cause more than half of the people in Yangzhou city to be infected within a month.If the Zero-COVID strategy were delayed for one week,the peak number of the infection wave would be 21.8 times more of what had happened in Yangzhou,and if it were delayed for two weeks,the peak size could reach 618 times higher.The qualitative and quantitative results provide an insightful reference for decision-making if the Zero-COVID policy and trace-test-quarantine strategy are adopted.