COVID-19席卷全球，世界各地感染人数激增；在这种情况下，许多国家采取了一系列严格的非药物干预措施，使得确诊病例增长速度有所放缓。然而，部分国家随后逐步放松防控，导致2020年7月下旬病例数突增，引起全球密切关注。本研究评估了2020年1月至2021年2月全球各个国家和地区的COVID-19大流行情况。我们计算了每个国家或地区的时依再生数[R(t)]，结果表明，世界上几乎一半的国家和地区从未控制过疫情。在曾经控制住疫情的国家和地区中，近一半未能维持疫情防控，导致全球疫情出现反弹，其中一半国家或地区反弹疫情规模比第一波更大。本研究还提出并使用时依的国家级传播风险评分(CTRS)，考虑到R(t)和每天的新增病例，以展示国家或地区一级的传播潜力和趋势。利用时依CTRS进行时依层次聚类，成功发现了促使2020年最后一个季度和2021年初全球COVID-19大流行加剧的国家和地区，并提示近期内COVID-19传播风险增加的国家和地区。此外，回归分析表明，实施和放松包括关闭工作场所和居家隔离在内的非药物干预措施，可能与最近的全球COVID-19传播变化有关。总而言之，对过去一年全球COVID-19大流行进行的系统评估表明，世界目前处于一种未曾设想的状况，各国在第一波疫情中吸取的教训有限。总结经验教训有助于制定有效的公共应对措施，以遏制全球未来的COVID-19疫情浪潮。

The occurrence of coronavirus disease 2019 (COVID-19) was followed by a small burst of cases around the world; afterward, due to a series of emergency non-pharmaceutical interventions (NPIs), the increasing number of confirmed cases slowed down in many countries. However, the lifting of control measures by the government and the public's loosening of precautionary behaviors led to a sudden increase in cases, arousing deep concern across the globe. arousing deep concern across the globe. This study evaluates the situation of the COVID-19 pandemic in countries and territories worldwide from January 2020 to February 2021. According to the time-varying reproduction number (R(t)) of each country or territory, the results show that almost half of the countries and territories in the world have never controlled the epidemic. Among the countries and territories that had once contained the occurrence, nearly half failed to maintain their prevention and control, causing the COVID-19 pandemic to rebound across the world—resulting in even higher waves in half of the rebounding countries or territories. This work also proposes and uses a time-varying country-level transmission risk score (CTRS), which takes into account both R(t)
and daily new cases, to demonstrate country-level or territory-level transmission potential and trends. Time-varying hierarchical clustering of time-varying CTRS values was used to successfully reveal the countries and territories that contributed to the recent aggravation of the global pandemic in the last quarter of 2020 and the beginning of 2021, and to identify countries and territories with an increasing risk of COVID-19 transmission in the near future. Furthermore, a regression analysis indicated that the introduction and relaxation of NPIs, including workplace closure policies and stay-at-home requirements, appear to be associated with recent global transmission changes. In conclusion, a systematic evaluation of the global COVID-19 pandemic over the past year indicates that the world is now in an unexpected situation, with limited lessons learned. Summarizing the lessons learned could help in designing effective public responses for constraining future waves of COVID-19 worldwide.