This paper investigates the lockdowns to contain the spread of the SARS-CoV-2 coronavirus in France, Germany, Italy, Spain, the UK and the US and also recent developments since these lockdowns have been relaxed. The analysis employs a two-stage SEIR model with different reproductive numbers pre- and post-lockdown. These parameters are estimated from data on the daily number of confirmed cases in a process that automatically detects the time at which the lockdown became effective. The model is evaluated by considering its predictive accuracy on current data and is then extended to a three-stage version to explore relaxations. The results show the extent to which each country was successful in reducing the reproductive number and demonstrate how the approach is able to model recent increases in the number of cases in all six countries, including the second peak in the US. The results also indicate that the current levels of relaxation in all five European countries could lead to significant second waves that last longer than the corresponding first waves. While there is uncertainty about the implications of these findings at this stage, they do suggest that a lot of vigilance is needed.

本文调查了法国、德国、意大利、西班牙、英国和美国为遏制 SARS-CoV-2 冠状病毒传播而采取的封锁措施，以及放松封锁后的最新进展。该分析采用了两阶段 SEIR 模型，该模型在封锁前后具有不同的繁殖数量。这些参数是根据每日确诊病例数数据估算得出的，该过程会自动检测锁定生效的时间。该模型通过考虑其对当前数据的预测准确性进行评估，然后扩展到三阶段版本以探索松弛。结果显示了每个国家在减少再生数方面成功的程度，并展示了该方法如何能够模拟所有六个国家最近病例数的增加，包括美国的第二次高峰。结果还表明，所有五个欧洲国家目前的放松水平可能会导致明显的第二波浪潮，其持续时间比相应的第一波浪潮更长。虽然现阶段这些发现的影响还存在不确定性，但它们确实表明需要高度警惕。