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“群体免疫”或许可行,但是代价有多大?

“群体免疫”或许可行,但是代价有多大?

Lauarie Garrett, John Moore 2020年07月30日
采用群体免疫策略的瑞典出现更多的死亡病例,瑞典经济也没有比其他的国家恢复得更好。

从华尔街到主街,处于新冠疫情中的人们对“群体免疫”给予了厚望。该理念认为,足够数量的人群最终会产生抗体,从而阻止病毒的传播,并抑制疫情的发展。基于这一点,美国总统唐纳德•特朗普也坚定地认为:“病毒将会消失,一定会消失。”

不出所料,新冠病毒群体免疫策略在瑞典失败了。人类通常会公然挑战整个群体的最大利益,劳瑞•加勒特和约翰•摩尔写道。图片来源:ALEXI ROSENFELD—GETTY IMAGES

瑞典政府在春季选择采用群体免疫策略,当时新冠疫情正在诸多欧洲国家肆虐。瑞典人民更赞成自愿控制举措,而不是严格的封锁令。本周,21名瑞典传染病专家发文谴责了这项政策,他们写道:“在瑞典,这一策略导致了死亡、悲伤和痛苦。更重要的是,没有迹象表明瑞典的经济要比其他很多国家更好。眼下,我们已经成为了全世界的一个典型案例,也就是不应该采用哪种方式来应对这一致命的传染病。”

英国在3月也曾经认真考虑过群体免疫策略,但很快因为死亡人数的上升而放弃,而且首相约翰逊也因为感染新冠病毒而住院。

群体免疫的问题在于“群体”一词。约400种疫苗已经被用于全球的禽畜、鱼、宠物和动物园动物:也就是所有那些没有自由意愿的生物。在出现某一疾病时,人们能够通过在某一群体内传播病原体,以牺牲部分群体的代价让幸存者产生免疫力,从而达到保护整个群体的目的。我们也可以通过向种群中足够数量的个体注射疫苗,以更小的生命代价来实现同样的结果。在这两种情况下,需要保护的比例取决于病原体的传染力。例如,如果70%的家养犬都注射了狂犬疫苗,那么全球的犬科群体就能得到保护,而且即便被狗咬也不会传播这种致命的病毒。

人类有其自由意愿,包括选择做各类蠢事的能力,尽管这些蠢事会让自己和他人成为高风险易感人群。这些人对约束感到焦躁不安,对限制十分不满,而且通常会漠视群体的最大利益。

从新冠病毒的建模可以得知,要保护剩余随心所欲的人类群体,那么感染率需要达到65%至70%。因此,在疫情从群体性灾难转变为偶发事件之前,三分之二的美国人口必须对病毒产生抗体。然而,让约2亿美国人感染意味着死亡人数将过百万,这个数字从道德上来讲着实让人无法接受。瑞典10%的人产生了抗体,西班牙流感疫情的幸存者有5%产生了抗体,伦敦参与新冠疫情病患护理的医疗工作者有45%产生了抗体,但这些数字离群体免疫水平都还相差甚远。

一项研究显示,在今春美国10个城市采集的血液标本中,3月/4月疫情高峰期间纽约市的血清阳性率最高,达到了22.7%。然而该市的首席医疗官杰•弗马称,这个数字也没有什么好庆幸的,因为我们很难用“群体免疫”来解释这个现象……要让免疫力在阻隔病毒传播过程中发挥主要作用,这个数字还远远不够。

此外,抗体测试呈阳性并不能保证免疫就能奏效;检测到的抗体可能还不足以对付病毒,或者不具有靶向性。这一点看起来似是而非,但危重病患的抗体反应是最强烈的,包括那些已经死亡的人士。无症状感染者或轻症患者的免疫反应通常较弱。

人们通常认为,那些恢复得快的人拥有强有力的病毒抗体,这种看法是有问题的。我们并不清楚较弱的抗体反应是否能够抵御再感染,而且T细胞免疫机制的触发仍然是一个未解之谜。有越来越多的个体案例报道称,一些个体在感染后得以治愈,而且病毒检测为阴性,但数周后再次被感染并突然生病。这些案例很少,但可能会变得更常见。

关键问题在于期限:新冠病毒免疫能力能够持续多长时间?我们依然处于这场疫情的初期。没有研究能够在超过三个月的时间内跟踪人们的免疫反应。研究结果则是喜忧参半。在纽约市,当地研究人员称,人们似乎在三个月之后依然有着强劲的免疫力。但伦敦的一项调查显示,免疫力在这个期间会逐渐变弱。在中国万州地区,40%的无症状感染者和12.9%的新冠病患很快成为了无抗体人群。

这类发现并不令人吃惊。人体对于引发普通感冒的冠状病毒的免疫力在一年之后就会消失,因此人们会不断得感冒。没有人会去探讨用群体免疫疗法来对付感冒病毒,因为这种做法毫无作用。

如果以感染为手段的群体免疫疗法无法奏效,那么我们就需要使用疫苗。Operation Warp Speed(一家公私合营项目,旨在加速新冠疫苗开发和配送)的多个候选疫苗已经在人体试验中激发了抗体和T细胞,但至于这些疫苗是否能够防止感染或缓解病症严重程度,现在做结论还为时尚早。只有大规模的疗效试验才可以提供这些急需的答案。然而,疫情的紧急性以及带来的其他压力可能意味着,远在我们了解这些疫苗的保护时限之前,它们可能已经得到了大规模应用批准。至于疫苗是否能够让70%的人群维持免疫力,没有人会愿意为此等上一年的时间。

可以预测的是,首款获批新冠疫苗所带来的免疫力将随着时间的流逝逐渐消失,因此需要多次进行加强注射。

当然,疫苗只有在广泛接种之后才能带来群体免疫。意见调查显示,很多美国“群体”人员已经决定拒绝使用新冠疫苗。5月的调查结果显示,仅有49%的人愿意注射疫苗,31%的人表示不确定,但有20%的人在任何情况下都会拒绝。7月的调查亦得到了类似发人深省的结果。一个科学特别小组警告说,Operation Warp Speed疫苗举措“基于一个令人信服但缺乏依据的假设:‘如果我们开发疫苗,那么人们就会接种。’”

为了提振公众信心,我们必须确保疫苗只有在疗效和安全性得到严格的检测通过之后才能获批。任何贸然的政治干预以及有碍安全评估的选举年政治手段,可能会进一步助长公众的不信任心理,继而让大众免疫接种成为空谈。

正如一名知名经济学家所说的那样:“绝对的经济恢复取决于新冠疫情的消失。现实在于,疫苗的时间线、疗效、成本和配送都存在一些问题,我们认为市场和公众意见并未充分意识到这些问题。”

只要人类行为允许新冠病毒在群体中传播,这种致命的病毒就不会简单地“消失”。华尔街式的奇迹——全体人群会突然获得强有力的持续免疫力,并允许全球经济回归2019年的水平——是不现实的。在研发出某款疫苗或多种疫苗、并通过在全球范围内使用来赋予人类群体免疫力之前,人类必须按照自由意愿,通过使用口罩、社交隔离和一些有效的常识性老办法,来保护自身和其他人群。(财富中文网)

劳瑞•加勒特是获得过普利策奖的科普文章作者,著有《背叛信任:全球公共卫生的倒塌》(Betrayal of Trust: The Collapse of Global Public Health)一书以及其他书作,他也是MSNBC新闻的科学撰稿人。

约翰•摩尔是威尔康奈尔医学院微生物学和免疫学教授,他一直在研究艾滋病病毒,最近在研究新冠病毒,中和抗体以及S糖蛋白。

译者:Feb

从华尔街到主街,处于新冠疫情中的人们对“群体免疫”给予了厚望。该理念认为,足够数量的人群最终会产生抗体,从而阻止病毒的传播,并抑制疫情的发展。基于这一点,美国总统唐纳德•特朗普也坚定地认为:“病毒将会消失,一定会消失。”

瑞典政府在春季选择采用群体免疫策略,当时新冠疫情正在诸多欧洲国家肆虐。瑞典人民更赞成自愿控制举措,而不是严格的封锁令。本周,21名瑞典传染病专家发文谴责了这项政策,他们写道:“在瑞典,这一策略导致了死亡、悲伤和痛苦。更重要的是,没有迹象表明瑞典的经济要比其他很多国家更好。眼下,我们已经成为了全世界的一个典型案例,也就是不应该采用哪种方式来应对这一致命的传染病。”

英国在3月也曾经认真考虑过群体免疫策略,但很快因为死亡人数的上升而放弃,而且首相约翰逊也因为感染新冠病毒而住院。

群体免疫的问题在于“群体”一词。约400种疫苗已经被用于全球的禽畜、鱼、宠物和动物园动物:也就是所有那些没有自由意愿的生物。在出现某一疾病时,人们能够通过在某一群体内传播病原体,以牺牲部分群体的代价让幸存者产生免疫力,从而达到保护整个群体的目的。我们也可以通过向种群中足够数量的个体注射疫苗,以更小的生命代价来实现同样的结果。在这两种情况下,需要保护的比例取决于病原体的传染力。例如,如果70%的家养犬都注射了狂犬疫苗,那么全球的犬科群体就能得到保护,而且即便被狗咬也不会传播这种致命的病毒。

人类有其自由意愿,包括选择做各类蠢事的能力,尽管这些蠢事会让自己和他人成为高风险易感人群。这些人对约束感到焦躁不安,对限制十分不满,而且通常会漠视群体的最大利益。

从新冠病毒的建模可以得知,要保护剩余随心所欲的人类群体,那么感染率需要达到65%至70%。因此,在疫情从群体性灾难转变为偶发事件之前,三分之二的美国人口必须对病毒产生抗体。然而,让约2亿美国人感染意味着死亡人数将过百万,这个数字从道德上来讲着实让人无法接受。瑞典10%的人产生了抗体,西班牙流感疫情的幸存者有5%产生了抗体,伦敦参与新冠疫情病患护理的医疗工作者有45%产生了抗体,但这些数字离群体免疫水平都还相差甚远。

一项研究显示,在今春美国10个城市采集的血液标本中,3月/4月疫情高峰期间纽约市的血清阳性率最高,达到了22.7%。然而该市的首席医疗官杰•弗马称,这个数字也没有什么好庆幸的,因为我们很难用“群体免疫”来解释这个现象……要让免疫力在阻隔病毒传播过程中发挥主要作用,这个数字还远远不够。

此外,抗体测试呈阳性并不能保证免疫就能奏效;检测到的抗体可能还不足以对付病毒,或者不具有靶向性。这一点看起来似是而非,但危重病患的抗体反应是最强烈的,包括那些已经死亡的人士。无症状感染者或轻症患者的免疫反应通常较弱。

人们通常认为,那些恢复得快的人拥有强有力的病毒抗体,这种看法是有问题的。我们并不清楚较弱的抗体反应是否能够抵御再感染,而且T细胞免疫机制的触发仍然是一个未解之谜。有越来越多的个体案例报道称,一些个体在感染后得以治愈,而且病毒检测为阴性,但数周后再次被感染并突然生病。这些案例很少,但可能会变得更常见。

关键问题在于期限:新冠病毒免疫能力能够持续多长时间?我们依然处于这场疫情的初期。没有研究能够在超过三个月的时间内跟踪人们的免疫反应。研究结果则是喜忧参半。在纽约市,当地研究人员称,人们似乎在三个月之后依然有着强劲的免疫力。但伦敦的一项调查显示,免疫力在这个期间会逐渐变弱。在中国万州地区,40%的无症状感染者和12.9%的新冠病患很快成为了无抗体人群。

这类发现并不令人吃惊。人体对于引发普通感冒的冠状病毒的免疫力在一年之后就会消失,因此人们会不断得感冒。没有人会去探讨用群体免疫疗法来对付感冒病毒,因为这种做法毫无作用。

如果以感染为手段的群体免疫疗法无法奏效,那么我们就需要使用疫苗。Operation Warp Speed(一家公私合营项目,旨在加速新冠疫苗开发和配送)的多个候选疫苗已经在人体试验中激发了抗体和T细胞,但至于这些疫苗是否能够防止感染或缓解病症严重程度,现在做结论还为时尚早。只有大规模的疗效试验才可以提供这些急需的答案。然而,疫情的紧急性以及带来的其他压力可能意味着,远在我们了解这些疫苗的保护时限之前,它们可能已经得到了大规模应用批准。至于疫苗是否能够让70%的人群维持免疫力,没有人会愿意为此等上一年的时间。

可以预测的是,首款获批新冠疫苗所带来的免疫力将随着时间的流逝逐渐消失,因此需要多次进行加强注射。

当然,疫苗只有在广泛接种之后才能带来群体免疫。意见调查显示,很多美国“群体”人员已经决定拒绝使用新冠疫苗。5月的调查结果显示,仅有49%的人愿意注射疫苗,31%的人表示不确定,但有20%的人在任何情况下都会拒绝。7月的调查亦得到了类似发人深省的结果。一个科学特别小组警告说,Operation Warp Speed疫苗举措“基于一个令人信服但缺乏依据的假设:‘如果我们开发疫苗,那么人们就会接种。’”

为了提振公众信心,我们必须确保疫苗只有在疗效和安全性得到严格的检测通过之后才能获批。任何贸然的政治干预以及有碍安全评估的选举年政治手段,可能会进一步助长公众的不信任心理,继而让大众免疫接种成为空谈。

正如一名知名经济学家所说的那样:“绝对的经济恢复取决于新冠疫情的消失。现实在于,疫苗的时间线、疗效、成本和配送都存在一些问题,我们认为市场和公众意见并未充分意识到这些问题。”

只要人类行为允许新冠病毒在群体中传播,这种致命的病毒就不会简单地“消失”。华尔街式的奇迹——全体人群会突然获得强有力的持续免疫力,并允许全球经济回归2019年的水平——是不现实的。在研发出某款疫苗或多种疫苗、并通过在全球范围内使用来赋予人类群体免疫力之前,人类必须按照自由意愿,通过使用口罩、社交隔离和一些有效的常识性老办法,来保护自身和其他人群。(财富中文网)

劳瑞•加勒特是获得过普利策奖的科普文章作者,著有《背叛信任:全球公共卫生的倒塌》(Betrayal of Trust: The Collapse of Global Public Health)一书以及其他书作,他也是MSNBC新闻的科学撰稿人。

约翰•摩尔是威尔康奈尔医学院微生物学和免疫学教授,他一直在研究艾滋病病毒,最近在研究新冠病毒,中和抗体以及S糖蛋白。

作者:Lauarie Garrett, John Moore

译者:Feb

From Wall Street to Main Street, much hope in the COVID-19 crisis has been placed on “herd immunity,” the idea that a sufficient number of people will eventually develop antibodies to stop virus spread and curtail the pandemic. That thinking is behind President Donald Trump’s insisting, “The virus will disappear. It will disappear.”

The Swedish government chose to pursue herd immunity during the spring when COVID-19 overwhelmed many European nations, favoring voluntary control measures over strict lockdown procedures. This week, 21 Swedish infectious diseases experts denounced the policy, writing, “In Sweden, the strategy has led to death, grief, and suffering, and on top of that there are no indications that the Swedish economy has fared better than in many other countries. At the moment, we have set an example for the rest of the world on how not to deal with a deadly infectious disease.”

The United Kingdom also flirted with a herd immunity strategy in March, but it soon backtracked as the death toll rose and Prime Minister Boris Johnson was hospitalized with COVID-19.

The problem with herd immunity is the word “herd.” Some 400 vaccines are used on livestock, fish, pets, and zoo animals worldwide: all creatures without free will. A herd can be protected against a disease by allowing a pathogen to spread within it, killing some but leaving the survivors resistant to infection. The same outcome can be achieved, at less cost in lives, by vaccinating a sufficient percentage of the herd. In both scenarios, the percentage needing protection depends on the pathogen’s infectiousness. For example, if 70% of domestic dogs are vaccinated against rabies, the worldwide canine herd is protected and dog bites do not transmit this lethal virus to humans.

In a democracy, humans have free will, including the ability to choose to do idiotic things that put themselves and others at high risk for infection. They chafe at restriction, bridle at confinement, and often defy the best interests of the herd.

Modeling of SARS-CoV-2 indicates that an infection rate of 65% to 70% is needed to protect the rest of our freewheeling human herd. Thus, two-thirds of the U.S. population must become resistant to the virus before our epidemic shifts from collective catastrophe to isolated incidents. But allowing infection of about 200 million Americans translates to more than 1 million deaths, a morally reprehensible toll. The 10% antibody-positive rate among Swedes, the 5% seen in survivors of Spain’s epidemic, and even the 45% found among London health care workers involved in COVID-19 patient care come nowhere near herd immunity levels.

A study of blood samples collected this spring in 10 U.S. cities found the highest seropositivity rate, 22.7%, was in New York City at its March/April epidemic peak. The city’s chief medical officer, Jay Varma, says, however, that this antibody rate offers no solace, since “herd immunity is a very unlikely explanation…We’re not nearly at a level where we would expect that immunity would play a major role in decreasing transmission.”

Moreover, a positive result on an antibody test does not guarantee protective immunity; the detected antibodies may be neither strong enough to counter the virus nor targeted appropriately. It seems paradoxical, but the strongest antibody responses are seen in the sickest patients, including those who die. People with asymptomatic or mild infections usually develop weak responses.

The common perception that someone who recovered quickly had strong antibodies that “beat the virus” is flawed. It’s unknown whether the weaker antibody responses are protective against reinfection, and we’re still foggy on how T cell immunity kicks in. Isolated cases are increasingly reported of individuals who survived COVID-19, tested negative for the virus, and then weeks later were reinfected and took ill. These cases are rare but may become more common.

The key issue is duration: How long does immunity to SARS-CoV-2 last? We are still very early in this pandemic. No studies have tracked immune responses in people for much longer than three months. Results are mixed. In New York City, local researchers say people seem to still be robustly immune after three months. But a London study saw immunity waning strongly over that period, and in the Chinese district of Wanzhou, 40% of asymptomatically infected people and 12.9% of COVID-19 cases rapidly became antibody-negative.

Such findings should come as no surprise. Immunity to the related coronaviruses that cause common colds wanes after about a year, so people can catch colds over and over again. Nobody discusses herd immunity for common cold viruses—because there is no such thing.

If herd immunity via infections is off the table, the world needs a vaccine. Several Operation Warp Speed (a public-private program designed to speed up COVID-19 vaccine development and distribution) vaccine candidates have elicited antibodies and T cells in human trials, but it’s too early to tell whether any will protect against infection or reduce the severity of disease. Only large-scale efficacy trials can provide those much-needed answers. However, the urgency of the pandemic and other pressures will probably mean that vaccines will be approved for mass use well before we know their duration of protection. Nobody wants to wait a full year to see if immunity is sustained for 70% of the human herd.

It is quite foreseeable that immunity to the first approved COVID-19 vaccines will diminish over time, requiring frequent booster injections.

Of course, a vaccine can only confer herd immunity if it is widely used. Opinion surveys show many American “herd” members have already decided to reject a SARS-CoV-2 vaccine. Polling results in May found only 49% would take it, and 31% were unsure, while 20% would refuse a vaccine under any circumstances. A July survey found similarly sobering results. A scientific task force has warned that the Operation Warp Speed vaccine effort “rests upon the compelling yet unfounded presupposition that ‘if we build it, they will come.’”

To boost public confidence, it is essential that vaccines are approved only after both efficacy and safety are rigorously proved. Any rushed political interventions and election year politics that compromise safety assessments could render mass immunization impossible by further fostering public distrust.

As prominent economists have put it, “Absolute economic recovery rests on the eradication of COVID-19. The reality is that the timeline, efficacy, cost, and distribution of a vaccine all introduce factors that we do not believe are appropriately reflected in the markets and public sentiment.”

This killer coronavirus will not simply “disappear” as long as human behavior allows it to spread within the herd. A Wall Street miracle, where powerful, lasting immunity emerges en masse and allows the world economy to return to its 2019 ways, is delusional. Until a vaccine or multiple vaccines are developed and used on a global scale to confer herd immunity, human beings must exercise free will to protect themselves and the rest of the human herd by using masks, social distancing, and good old-fashioned common sense.

Laurie Garrett is a Pulitzer Prize–winning science writer, author of Betrayal of Trust: The Collapse of Global Public Health and other books, and a science contributor for MSNBC News.

John Moore is a professor of microbiology and immunology at Weill Cornell Medicine who has conducted research on HIV and, more recently, SARS-CoV-2, neutralizing antibodies, and spike glycoproteins.

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