The community lockdown measures implemented in the United States from late March to late May of 2020 resulted in a significant reduction in the community transmission of the COVID-19 pandemic throughout the country. However, a number of US states are currently experiencing an alarming post-lockdown resurgence of the pandemic, triggering fears for a devastating second pandemic wave. We designed a mathematical model for addressing the key question of whether or not the universal use of face masks can halt such resurgence (and possibly avert a second wave, without having to undergo another cycle of major community lockdown) in the states of Arizona, Florida, New York and the entire US. Model calibration, using cumulative mortality data for the four jurisdictions during their respective pre-lockdown and lockdown periods, show that pre-symptomatic and asymptomatically-infectious individuals are, by far, the main drivers of the COVID-19 pandemic in each of the jurisdictions. The implication of this result is that detecting and isolating individuals with clinical symptoms of the pandemic alone (even if all of them are found) may not be sufficient to effectively curtail the pandemic. To achieve such control, it is crucially-necessary that pre-symptomatic and asymptomatically-infectious individuals are rapidly detected and isolated (and their contacts rapidly traced and tested). Our study highlights the importance of early implementation of the community lockdown measures. In particular, a sizable reduction in the burden of the pandemic would have been recorded in each of the four jurisdictions if the community lockdown measures were implemented a week or two earlier. These reductions are significantly increased if the early implementation of the lockdown measures was complemented with a public face mask use strategy. With all related control measures maintained at their baseline levels, this study shows that the pandemic would have been almost completely suppressed from significantly taking off if the lockdown measures were implemented two weeks earlier, and if a sizable percentage of the residents of the four jurisdictions wore face masks during the respective lockdown periods. The burden of the second wave of the pandemic would have been reduced significantly if the lockdown measures were extended by two weeks. We simulated the pandemic in the four jurisdictions under three levels of lifting of community lockdown, namely mild, moderate and high. For the scenario where the control measures adopted are maintained at their baseline levels during the lockdown period, our simulations show that the states of Arizona and Florida will record devastating second waves of the pandemic by the end of 2020, while the state of New York and the entire US will record milder second waves. If the community lockdown measures were lifted at the mild lifting level (i.e., only limited community contacts and business activities are allowed, in comparison to the levels of these activities allowed during the corresponding lockdown period), only the state of Florida will experience a second wave. It is further shown that the severity of the projected second waves depend on the level of lifting of the community lockdown. For instance, the projected second wave for Arizona and Florida will be more severe than their respective first waves. It is further shown that, for high level of lifting of community lockdown measures, the increased use of face masks after the lockdown period greatly reduces the burden of the pandemic in each jurisdiction. In particular, for this high lockdown lifting scenario, none of the four jurisdictions will experience a second wave if half of their residents wear face masks consistently after their respective lockdown period. A diagnostic testing strategy that increases the maximum detection rate of asymptomatic infected individuals (followed by contact tracing and self-isolation of the detected cases) greatly reduces the burden of the pandemic in all four jurisdictions, particularly if also combined with a universal face mask use strategy. Finally, it is shown that the universal use of face masks in public, with at least moderate level of compliance, could halt the post-lockdown resurgence of COVID-19, in addition to averting the potential for (and severity of) a second wave of the pandemic in each of the four jurisdictions.

从2020年3月下旬至2020年5月下旬，美国实施了社区封锁措施，从而大大减少了COVID-19大流行在全国范围内的社区传播。但是，美国许多州目前正经历令人震惊的大流行停滞后复活，引发了对毁灭性第二次大流行浪潮的担忧。我们设计了一个数学模型来解决以下关键问题：在佛罗里达州亚利桑那州，普遍使用口罩是否可以制止这种死灰复燃（并可能避免第二波浪潮，而不必经历另一个主要社区封锁的周期） ，纽约和整个美国。使用四个辖区在各自的锁定前和锁定期期间的累积死亡率数据进行模型校准，研究表明，到目前为止，在每个辖区中，有症状和无症状感染者都是导致COVID-19大流行的主要因素。该结果的含义是，仅检测和隔离仅具有大流行的临床症状的患者（即使发现了所有症状）可能不足以有效地遏制大流行。为了实现这种控制，至关重要的是，必须迅速检测和隔离有症状和无症状感染前的个体（并迅速追踪和测试其接触）。我们的研究强调了尽早实施社区封锁措施的重要性。尤其是，如果提前一周或两周实施社区封锁措施，则在四个辖区中的每个辖区都将大幅度减轻流行病负担。如果尽早实施锁定措施并辅之以公共口罩使用策略，这些减少量将大大增加。在所有相关控制措施都维持在基线水平的情况下，这项研究表明，如果在两周前实施锁定措施，并且四个辖区的居民中有相当一部分人穿上了大流行的衣服，大流行将几乎完全被抑制，从而免于大流行。各个锁定期间内的口罩。如果将封锁措施延长两周，第二波大流行的负担将大大减轻。我们在解除社区封锁的三个级别（即轻度，中度和高度）下模拟了四个辖区的大流行。对于在锁定期间所采取的控制措施维持在基线水平的情况，我们的模拟显示，到2020年底，亚利桑那州和佛罗里达州将记录毁灭性的第二波大流行，纽约州和佛罗里达州整个美国将录得温和的第二波浪潮。如果将社区封锁措施的解除程度提高了（例如，与相应封锁期间允许的活动水平相比，只允许有限的社区联系和商业活动），则只有佛罗里达州会经历一秒钟波。进一步表明，预计的第二波浪的严重程度取决于社区封锁的解除程度。例如，预计亚利桑那州和佛罗里达州的第二波将比其各自的第一波更为严峻。进一步表明，为了高度取消社区封锁措施，在封锁期后增加使用口罩将大大减轻每个辖区的大流行负担。特别是，对于这种高度锁定解除的情况，如果四个辖区的一半居民在各自的锁定期后始终戴着口罩，则不会再经历第二次浪潮。一种诊断测试策略，可以提高无症状感染者的最大检出率（通过接触追踪和所发现病例的自我隔离），可以大大减轻所有四个辖区的大流行负担，特别是如果还结合使用通用口罩的话战略。最后，