全球新冠开始神秘大撤退！专家也不解

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《新冠，正在撤退》！

这是纽约时报刊发于10月4日的独家报道，标题令人振奋。

纽约时报报道显示，过去一个月，美国新增病例数下降了三分之一以上。具体原因尚不清楚，同时也不能保证病例数将在未来持续下降。但结合现阶段的转折点，以及其持续时长来看，全球医学界已开始关注这一特殊变化。

自今年9月1日以来，美国每日新增病例数量显著下降了35%。而自8月底以来，全球范围内的病例数也显著下降了30%以上。上周，美国斯克里普斯研究所（Scripps Research）的埃里克·托波尔（Eric Topol）博士写道：“这是数月来所观察到的特别良好的情况。”

目前，各国专家也不清楚染疫人数为何急剧下降，不过其中的确存在一种神秘的“两个月的循环周期”：即升温2个月后接着衰退2个月，但专家强调这不代表疫情就此终结。

此外，根据Worldometer统计，若自8月19日疫情高峰起算，单日新增人数一度达74.6万人，但10月4日单日新增人数已降至34.5万人，下降幅度超过53%。

对于上述的2个月神秘周期，许多人猜测可能和季节性或是社交距离政策有关，不过纽约时报指出，2个月周期在各个季节都发生过，甚至在人们没有严格遵守社交距离政策的时候也出现过。

因此最符合常理的解释是病毒的生物性，结合了人类的社交行为。例如：不同的变异毒株特易传染特定的人类族群，当这些脆弱族群都已经感染过后，病毒自然就消退了。另外，也可能是每一种变异株需要2个月的时间，才能在一般大小的社区中传播。

纽约时报认为，隔离封锁措施的确发挥了作用，因为一旦疫情数量开始飙升，人们就会变得愈发谨慎。但明尼苏达大学流行病学家欧斯特荷姆（Michael Osterholm）认为，保持社交距离其实不如我们以为的那么重要，因为目前数百万美国儿童已经返校上课，近期的确诊人数却仍持续下降。

只是不管出于什么原因，两个月的神秘周期一直在不断循环，而且这在全球的数字中是显然可见的。今年，美国病例数目从2月底到4月底上升，然后下降到6月底。紧接着，又在8月底再次上升，此后一直处于下降趋势。

不仅如此，更鼓舞人心的消息是，新冠重症病例也在不断下降。自9月1日以来，因新冠住院的美国患者下降了约25%。而自9月20日以来，每日死亡人数也已经下降了10%。这是自初夏以来，美国疫情死亡人数的首次持续下降。

“最后一波大浪潮”?

如今，科学家对这种神秘周期存有太多疑问，甚至希望以此解开新冠之谜。

然而纽约时报强调，新冠病毒的两个月周期并不是什么铁定的科学规律，因为目前世界各地也存在很多例外。

例如，英国过去两个月的病例数量并没有持续下降，而是显得起伏不定。此外，随着美国寒冷天气的到来，人们将不断增加室内活动，届时是否会导致秋冬病例激增也未可知。因此，新冠大流行的发展仍然存在高度不确定性。

但这种不确定性也许暗示着，人们的未来会变得很乐观，因为越来越多的民众已接种至少一剂疫苗。此外，纽约时报称目前有一半的美国人或已感染新冠病毒，这甚至赋予了他们一些自然免疫力。

最终，只要人们的免疫系统进化得足够完善，像Delta那样具有破坏性的新一波疫情几乎永远不可能发生。

不过，许多科学家认为，新冠病毒也不会很快消失，它将循环往复多年。但疫苗可以将新冠转变为一种可控制的疾病，致使其与流感或普通感冒没有太大区别。

纽约时报结尾处写道：无论今秋人们会迎来什么，可以肯定的是，疫情最严重的阶段已经过去。

来自中国的消息：

在近期的第五届中阿博览会大健康产业论坛暨第三届“互联网+医疗健康”应用大会上。中国工程院院士钟南山和复旦大学附属华山医院感染科主任、国家传染病医学中心主任文宏医生都对疫情现状发表了重要讲话。

钟南山表示，Delta病毒重在预防，中国超80%人口接种新冠疫苗后，有望在年底建立有效的群体免疫。

钟南山分析了中国多个省市近三个月来Delta病毒株局部传播情况，他表示，Delta病毒株具有传染性强、潜伏期短、病毒载量高、转阴时间长的特点。

以广州发现的Delta病毒株为例，其传播链根据统计，大概1个可以传（染）4个，4个再传16个，以这样的比例，Delta病毒株经过四代后会大量传播。

他补充道：“所以现在（针对Delta病毒株），最关键的不是治疗，而是预防，要切断它的传播，这样才能够解决问题。”

关于群体免疫，钟南山表示：现在全世界都是采用大规模的疫苗接种来建立群体免疫，而这至少需要2~3年时间的全球协作。

在谈到什么时候可以做到回国免除隔离的问题时，复旦大学附属华山医院感染科主任、国家传染病医学中心主任张文宏没有明确表示。

但张文宏进一步说明：“世界各国有条件地恢复人员往来，今年下半年就会开始。我们希望中国在2022年上半年可以有条件地跟一些国家恢复往来，这取决于打疫苗的速度。”

中国目前正向全球其他国家大量供应疫苗，但由于其他更多国家疫苗供不应求，全球70多亿人口全部完成接种也得好几年。所以说，不管对于中国还是其他国家，开放国境这件事情都急不来。一步步稳扎稳打才能最大程度在开放的同时保持本土的安全。

但是可以确定的是，针对一些疫苗打得不错、发病率低的国家有条件地恢复往来，今年下半年就会开始。

纽约时报报道英文原文：

Covid, in Retreat

Covid-19 is once again in retreat.

The reasons remain somewhat unclear, and there is no guarantee that the decline in caseloads will continue. But the turnaround is now large enough — and been going on long enough — to deserve attention.

The number of new daily cases in the U.S. has fallen 35 percent since Sept. 1:

Worldwide, cases have also dropped more than 30 percent since late August. “This is as good as the world has looked in many months,” Dr. Eric Topol of Scripps Research wrote last week.

These declines are consistent with a pattern that regular readers of this newsletter will recognize: Covid’s mysterious two-month cycle. Since the Covid virus began spreading in late 2019, cases have often surged for about two months — sometimes because of a variant, like Delta — and then declined for about two months.

Epidemiologists do not understand why. Many popular explanations, like seasonality or the ebbs and flows of social distancing, are clearly insufficient, if not wrong. The two-month cycle has occurred during different seasons of the year and occurred even when human behavior was not changing in obvious ways.

The most plausible explanations involve some combination of virus biology and social networks. Perhaps each virus variant is especially likely to infect some people but not others — and once many of the most vulnerable have been exposed, the virus recedes. And perhaps a variant needs about two months to circulate through an average-sized community.

Human behavior does play a role, with people often becoming more careful once caseloads begin to rise. But social distancing is not as important as public discussion of the virus often imagines. “We’ve ascribed far too much human authority over the virus,” as Michael Osterholm, an infectious-disease expert at the University of Minnesota, has told me.

The recent declines, for example, have occurred even as millions of American children have again crowded into school buildings.

Hospitalizations, too

Whatever the reasons, the two-month cycle keeps happening. It is visible in the global numbers, as you can see in the chart below. Cases rose from late February to late April, then fell until late June, rose again until late August and have been falling since.

The pattern has also been evident within countries, including India, Indonesia, Thailand, Britain, France and Spain. In each of them, the Delta variant led to a surge in cases lasting somewhere from one and a half to two and a half months.

In the U.S., the Delta surge started in several Southern states in June and began receding in those states in August. In much of the rest of the U.S., it began in July, and cases have begun falling the past few weeks. Even pediatric cases are falling, despite the lack of vaccine authorization for children under 12, as Jennifer Nuzzo of Johns Hopkins University told The Washington Post. 

The most encouraging news is that serious Covid illnesses are also declining. The number of Americans hospitalized with Covid has fallen about 25 percent since Sept. 1. Daily deaths — which typically change direction a few weeks after cases and hospitalizations — have fallen 10 percent since Sept. 20. It is the first sustained decline in deaths since the early summer.

‘The last major wave’?

This is the part of the newsletter where I need to emphasize that these declines may not persist. Covid’s two-month cycle is not some kind of iron law of science. There have been plenty of exceptions.

In Britain, for example, caseloads have seesawed over the past two months, rather than consistently fallen. In the U.S., the onset of cold weather and the increase in indoor activities — or some other unknown factor — could cause a rise in cases this fall. The course of the pandemic remains highly uncertain.

But this uncertainty also means that the near future could prove to be more encouraging than we expect. And there are some legitimate reasons for Covid optimism.

The share of Americans 12 and over who have received at least one vaccine shot has reached 76 percent, and the growing number of vaccine mandates — along with the likely authorization of the Pfizer vaccine for children ages 5 to 11 — will increase the number of vaccinations this fall. Almost as important, something like one-half of Americans have probably had the Covid virus already, giving them some natural immunity.

Eventually, immunity will become widespread enough that another wave as large and damaging as the Delta wave will not be possible. “Barring something unexpected,” Dr. Scott Gottlieb, a former F.D.A. commissioner and the author of “Uncontrolled Spread,” a new book on Covid, told me, “I’m of the opinion that this is the last major wave of infection.”

Covid has not only been one of the worst pandemics in modern times. It has been an unnecessarily terrible pandemic. Of the more than 700,000 Americans who have died from it, nearly 200,000 probably could have been saved if they had chosen to take a vaccine. That is a national tragedy.

Covid also isn’t going to disappear anytime soon. It will continue to circulate for years, many scientists believe. But the vaccines can transform Covid into a manageable disease, not so different from a flu or common cold. In the past few weeks, the country appears to have moved closer to that less grim future.

Whatever this autumn brings, the worst of the pandemic is almost certainly behind us.

https://www.nytimes.com/2021/10/04/briefing/covid-caseload-retreat-us-cases.html

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