欧洲、中东、大洋洲、南亚部分地区和美国逐步退出COVID-19封锁,放松最严厉的社会疏导措施。

同时,中国、新加坡和韩国这些首先受到冲击并成功控制第一波的国家,在放松反COVID-19措施后似乎面临不同的动态。

South Korea appeared to have fully controlled local contagion, until 10 May (Hyonhee Shin, Josh Smith, “韩国争相控制夜总会冠状病毒的爆发“, 路透社,2020年5月11日)。两天内,韩国报告了 69个新病例 与首尔的夜总会和酒吧相联系,测试接触案例,仍然需要追踪3000多人。其边界被关闭,并且 参赛作品 被提交给严格的检疫。

China seemed to fare quite well, despite struggling with clusters and imported cases notably in Heilongjiang (William Yang, “中国试图控制新的冠状病毒疫情“, 邓小平, 29 April 2020). Then, on 11 May, just above a months after the end of the lockdown, a new cluster arose in Wuhan, the original center of the epidemic, linked to asymptomatic cases (“China’s Wuhan reports first coronavirus cluster since lifting of lockdown“, 路透社,2020年5月11日)。5月9日,是吉林省东北部报告了一个新的小型集群,这引发了对舒兰市的封锁(同上)。

新加坡知道什么可以被看作是第二波浪潮,重点是移民工人,案件开始成倍增加。 2020年4月初 (James Crabtree, “新加坡的第二波浪潮如何暴露出经济不平等现象“, 新政治家》杂志,2020年5月6日)。

Meanwhile, history shows that for the 1918-1919 so-called “Spanish” Influenza pandemic, the second and third waves were more lethal than the first spring wave (Jeffery K. Taubenberger and David M Morens, “1918年流感:所有大流行病之母," 新出现的传染病 vol. 12,1, 2006)。

因此,关于这个COVID-19第二波,我们在不久的将来会有什么期待?

流行病学家已经建立了各种类型的情景模型,以帮助政策制定者处理该大流行病,并制定尽可能减少死亡人数的对策。本文探讨了四种这样的模型和情景,并强调了它们对未来COVID-19浪潮的启示。将这些情景与中国、新加坡和韩国的现实情况进行简要比较,我们强调了看起来更有可能发生的情景,并强调了进一步研究其他因素的必要性。

作为我们与COVID-19相互作用的结果的波浪

现在人们普遍认为,我们将不得不与COVID-19共存。无论爆发的形式如何,预计这种大流行病都会持续下去,直到实现免疫,假设这是有可能的话。免疫将来自于疫苗接种或自然免疫。根据我们的估计,并考虑到需要制造数十亿剂量的免疫,在2022年冬季之前最好不要实现免疫(见Helene Lavoix, COVID-19大流行,生存与重建, The Red Team Analysis Society2020年3月24日)。这个时间框架没有考虑到开展大规模的疫苗接种活动所需的时间。

考虑到所有国家都措手不及,可能只有韩国例外,行动者们尽可能地处理了COVID-19的第一次爆发或第一波。一系列的措施被制定和应用,包括在全球范围内的严格封锁,这使得他们能够处理突发事件并减少死亡人数。这些措施的主要目的是阻止传染,同时不看到卫生系统崩溃。我们成功做到的不是结束疫情,而是改变其进程。我们避免了立即可能出现的最坏情况(Helene Lavoix, COVID-19大流行的最坏情况基线方案, The Red Team Analysis Society,2020年3月24日)。

然而,付出的代价是活动停止了,给生活方式,包括经济带来了巨大的损失。

现在,我们正在进入一个新的阶段,我们将开始学习与COVID-19共处。我们担心的是,一旦活动重新开始,那么这种流行病将再次蔓延和发展,带来第二波的死亡、痛苦和看到卫生系统崩溃的危险。因此,政治当局正急于设计一系列措施和政策,使我们能够与COVID-19一起生活,而不是被危险冻结,直到另一种死亡带走我们所有人。

第二波和下一波的可能性一般取决于病毒之间的相互作用,特别是SARS-CoV-2的流行病学,以及各方面的反应和行动将设计和实施。

因此,我们的活动既依赖于COVID-19的波浪,同时也有助于创造和塑造它们。

第二波和复发波

帝国理工学院COVID-19反应小组三月研究

首先,我们有帝国学院COVID-19反应小组的有影响力的研究。 非药物干预(NPIs)对降低COVID19死亡率和医疗需求的影响 (16 March 2020). Many governments used this report to build their first wave’s lockdown policies.

(从这一点出发,通过人工智能自动翻译法语)。

在这项研究中,目标是最大限度地减少死亡,这就要求不要让医院不堪重负,尤其是重症监护室的床位要求(ICU)的数量。考虑到的政策措施有以下几点。

  • 家庭中的病例隔离(CI)。
  • Voluntary home quarantine (for 14 days – HQ),
  • 70岁以上人士的社会疏远(SDO)。
  • Social distancing of entire population (similar to lockdown – SD),
  • 关闭学校和大学(PC)。

该研究除其他关键因素外,还考虑了 R0 (R-nought) or basic reproduction number of an infectious disease. This is a measure that represents “the expected number of secondary cases produced by a typical infected individual early in an epidemic” (O Diekmann; J.A.P. Heesterbeek and J.A.J. Metz (1990). "论异质种群中传染病模型中基本繁殖率R0的定义和计算"数学生物学杂志》(Journal of Mathematical Biology 28: 356–382). They “examine values between 2.0 and 2.6”, which is in the range of most estimates. They also take into account the acquired immunity against the SARS-CoV-2 and consider it to be similar to what is obtained against the seasonal influenza, i.e. re-infection cannot reoccur the next season.

通过这个模型,帝国学院COVID-19反应小组发现,对于一个 R0=2.2,在第一波结束后,一旦放松对全体居民的社会疏散措施,学校和大学重新开放,假设所有其他措施保持不变,新的一波开始。它引发了在放松措施开始一个月后,需要开始一个新的全民社会疏散和学校和大学关闭的时期。

As a whole, over two years, the full range of measures “is in force approximately 2/3 of the time” (p.12). In two years, we thus have, excluding the first wave, eleven waves of two months each, however the apex of each wave is lower. The second wave thus starts immediately once the lockdown stops, but starts being experienced as such one month after the exit strategy, when the need for SD is triggered.

帝国学院COVID-19反应小组 – 16 March study, p. 12 – “Figure 4: Illustration of adaptive triggering of suppression strategies in GB, for R0=2.2, a policy of all four interventions considered, an “on” trigger of 100 ICU cases in a week and an “off” trigger of 50 ICU cases.”

虽然还需要进一步监测,但这似乎与中国和韩国出现的新集群大致相符。然而,在这两个国家,我们离帝国理工学院估计的从禁闭状态退出后一个月在ICU的需求还很远,如上图所示。

The Harvard T.H. Chan School of Public Health’s model

Scientists of the Harvard T.H. Chan School of Public Health created a model allowing notably for different sensitivity of the virus to seasonality (Stephen M. Kissler, et al. “预测SARS-CoV-2在后流行期的传播态势“, 科学,2020年4月14日)。

It obtained scenarios similar to those of the Imperial College, with recurring waves into 2022 “requiring social distancing measures to be in place between 25% (for wintertime R0 = 2 and seasonality…) and 75% (for wintertime R0 = 2.6 and no seasonality …) of that time”.

很明显,越低 R0 考虑,季节性因素越重要,社会疏远期就越短。

Here, as for the Imperial College’s model, the second wave would start immediately as social distancing measures are relaxed. In the Harvard model, in the U.S. case, new social distancing measures would be needed one month after the end of SD if the virus is not seasonal. If the virus is seasonal and if the first wave took place in Spring, as is more or less the case in the U.S., new social distancing measures would be needed 2,5 months after the end of SD.

5月份在韩国和中国出现的新群组倾向于表明,该病毒不是或不具有强烈的季节性。无论如何,新加坡的病例和4月的浪潮表明,高温和潮湿似乎并不能阻止病毒和疾病的发生。

CIDRAP的三种可能情况

On 30 April 2020, the Centre for Infectious Disease Research and Policy (CIDRAP) of the University of Minnesota published “COVID-19大流行的未来:从流感大流行中吸取的教训,” (Kristine Moore, MD, MPH, Marc Lipsitch, DPhil, John Barry, MA, and Michael Osterholm, PhD, MPH).

CIDRAP指出了流感和SARS-CoV-2之间有用的相似之处,但也有不同之处,特别是后者的病毒传播性更强,它概述了三种可能的情况。这些设想给出了未来流感浪潮的前景,但还不够精确,无法估计第二波浪潮何时开始。

The first scenario of the CIDRAP is very similar to the scenario of the Imperial College and of Harvard T.H. Chan School of Public Health. According to this first scenario, “the first wave of COVID-19 in spring 2020 is followed by a series of repetitive smaller waves that occur through the summer and then consistently over a 1- to 2-year period, gradually diminishing sometime in 2021.” The strength and timing of waves may vary with the efficiency of the controlling measures taken as well as according to other demographic and geographic factors. This first scenario also expects that full SD measures may have to be implemented regularly.

CIDRAP’s second scenario is inspired by the pattern of the 1918-1919 Spanish Flu pandemic. “The first wave of COVID-19 in spring 2020 is followed by a larger wave in the fall or winter of 2020 and one or more smaller subsequent waves in 2021.” Thus, the main difference with the Imperial College and Harvard scenarios is first about intensity. The second wave is the most lethal. Second, it is about timing. The second wave would take place in the next fall or winter. Finally it is about the number of subsequent waves following the second one, creating two sub-scenarios: only one further wave or subsequent smaller waves.

Considering what is happening in China, Singapore and South Korea, the timing does not seem to correspond. The difference probably comes from the measures implemented for the COVID-19, which are likely to have “artificially” stopped the first wave, compared with the 1918 Influenza pandemic. However, the possibility of a more lethal second wave is serious enough to keep this scenario and further detail comparatively the 1918 pandemic and the COVID-19.

The third CIDRAP scenario is different from the previous models. It envisions that “the first wave of COVID-19 in spring 2020 is followed by a “slow burn” of ongoing transmission and case occurrence, but without a clear wave pattern.” In that case the most severe social distancing measures will not have to be reimplemented but “cases and deaths will continue to occur”.

This scenario does not fit what took place in Singapore. It may be, however, too early to discard it. It may also not be universal. In some countries, excess death and sufferings are not acceptable, while there is always the risk that contagion spreads again exponentially. Thus, even a few cases would trigger SD measures, as possibly in New Zealand, or in Shulan in China (e.g. Amy Gunia, “为什么新西兰的消除冠状病毒战略不太可能在大多数其他地方奏效?“, 时间,2020年4月28日;同上)。

流动性和第二波

最近的研究也是由帝国学院COVID-19反应小组进行的,重点是意大利(报告20:利用流动性来估计意大利COVID-19的传播强度:国家以下各级的分析与未来的设想,2020年5月4日)。

It models scenarios for a relaxation of isolation measures on 4 May 2020, using increase in mobility as a proxy. A second wave is quasi in-built in their model as mobility is the parameter used to make “the time related reproduction number or effective reproduction number (Rt)” change. Thus, what the model tells us is the extent of infection and death in excess, i.e. the size of the wave.

在所模拟的第一种情况下,流动性比封锁前的水平增加了20%,而在第二种情况下,流动性增加了40%。然而,这些情况并没有考虑到其他反COVID-19的措施,如学校关闭、卫生、口罩或测试和接触追踪。它只关注了流动性因素。

第一个发现,不出所料,就是情况因地区而异。 这可能表明,例如中国或德国处理COVID-19的方式可能是未来的方向,至少就流动性因素而言。

在情景1(20%流动性)中,超额死亡人数大约在2020年6月8日在皮埃蒙特、6月20日在威尼托和7月13日在托斯卡纳上升到100人以上,然后以指数形式上升。

在情景2(40%流动性)中,超额死亡人数大约在5月28日在皮埃蒙特,6月4日在威尼托,6月10日在托斯卡纳,6月22日在伦巴第,7月4日在艾米利亚-罗马涅和利古里亚上升到100以上,然后呈指数增长。

正如作者所强调的,这些情况必须被视为最坏的情况,因为知道其他措施将被实施。

因此,除了CIDRAP的第三种情况,所有的流行病学模型都表明我们将面临第二波。大多数模型还考虑了以下反复出现的浪潮。

现在,与中国、韩国和新加坡的疫情动态进行简单的比较,往往表明预计会出现反复的模型和情景是最有可能的。这也可能表明,除了新加坡的情况,模型在第二波的时间方面是悲观的。然而,在新加坡,流行病学模型中没有包括的其他因素也在起作用。同时,第二波的规模从而致命性仍然是一个高影响的不确定性,必须仔细考虑。

因此,我们能否找到其他有助于改善对未来浪潮评估的因素?这些因素将使预见性更加可操作。因此,它们将有助于设计有效的政策。这就是我们将在下一篇文章中看到的内容。

进一步的参考书目

Taubenberger, Jeffery K, and David M Morens."1918年流感:所有大流行病之母." 新出现的传染病 vol. 12,1 (2006):15-22. doi:10.3201/eid1201.050979

特色图片。图片来源 Elias Sch. 德 淘宝网 [公共领域]

由Dr Helene Lavoix (MSc PhD Lond)发布

Helene Lavoix博士伦敦大学博士(国际关系) ,是Red Team Analysis Society的总裁/CEO。她专门研究国际关系、国家和国际安全问题的战略预见和早期预警。她目前的工作重点是乌克兰战争、国际秩序和中国的崛起、行星越轨行为和国际关系、战略预见和预警方法、激进化以及新技术和安全。

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