Objective: To evaluate effectiveness of prevention and control strategies for COVID-19 in Ningbo by using an epidemic dynamic model. Methods: The incidence data and epidemic information of COVID-19 reported in Ningbo as of 9 March, 2020 were collected, and based on the implementation of prevention and control strategies, we developed a SEIR epidemic dynamics model. The basic and real-time reproduction numbers were calculated to evaluate effectiveness of prevention and control. Results: A total of 157 cases of COVID-19 were confirmed, without death, in Ningbo. The proportion of severe cases was 12.1%. The mean incubation period was estimated to be (5.7±2.9) days. The mean interval from illness onset to diagnosis was (5.4±3.7) days. The mean duration from diagnosis to hospital discharge was (16.6±6.5) days. A total of 105 339 contacts had been under medical observation. The infection rates in contacts with home quarantine and centralized quarantine were 0.1% and 0.3%, respectively. In the confirmed cases, those who had been under medical observation before diagnoses accounted for 63.1%. The basic reproduction number was estimated to be 4.8. With the strengthening of prevention and control measures, real-time reproduction number showed a gradual downward trend, dropping to below 1.0 on 4 February, and then continued to drop to 0.2 in mid-February. Conclusion: The effectiveness of the prevention and control measures for COVID-19 in Ningbo can be evaluated by using epidemic dynamic model to provide scientific evidence for the development of the prevention and control strategies.
目的： 基于传染病动力学模型评估宁波市新型冠状病毒肺炎（COVID-19）防控措施的效果。 方法： 收集截至2020年3月9日宁波市COVID-19疫情个案数据、疾病进程等信息。根据防控策略落实情况，建立SEIR传染病动力学模型，计算基本再生数（R(0)）和实时再生数（R(t)），评估防控效果。 结果： 宁波市累计确诊COVID-19病例157例，无死亡病例，重症病例比例为12.1%。从暴露到发病（潜伏期）平均（5.7±2.9）d，发病到确诊平均（5.4±3.7）d，从确诊到出院平均（16.6±6.5）d。累计医学观察105 339人，其中居家医学观察者COVID-19感染率为0.1%，集中医学观察者感染率为0.3%，确诊病例在就诊前处于医学观察期者占63.1%。估算R(0)为4.8。随着防控措施的加强，R(t)呈逐渐下降趋势，到2月4日下降至1.0以下，之后持续下降到2月中旬的0.2。 结论： 通过建立传染病动力学模型，能够有效评估宁波市COVID-19防控措施的效果，为防控策略的制定提供科学依据。.
Keywords: Basic reproduction number; COVID-19; Dynamic model; Effectiveness of prevention and control.