Kids and COVID: why young immune systems are still on top

亲娘啊，大概8号前后开始，到15号翻译完，除去周末，大概用了6天，每天空的时候花大概一个多小时到两个小时翻译一点点，终于弄完了。

nature好难啊，语法倒是没有太多的长难句，生词太多了。

看来很有可能要转战扇贝阅读了。

Innate immunity might be the key to why children have fared better with the virus. But the Delta variant poses fresh unknowns.

天生的免疫力可能是孩子们在对抗COVID-19病毒上比成年人表现更好的关键。但是德尔塔变异体又带来了全新未知的问题。

Early last year, children’s hospitals across New York City had to pivot to deal with a catastrophic COVID-19 outbreak.

去年初，整个纽约的儿童医院不得不转向去应对COVID-19灾难性的爆发。

“We all had to quickly learn — or semi-learn — how to take care of adults,” says Betsy Herold, a paediatric infectious-disease physician who heads a virology laboratory at the Albert Einstein College of Medicine.

“我们必须去快速的学习，或者半学习去照顾成年人”，爱因斯坦医学院的病毒实验室主任兼儿科传染病医生Betsy Herold说。

The reason: while hospitals across the city were bursting with patients, paediatric wards were relatively quiet. Children were somehow protected from the worst of the disease.

原因是：当整个城市的医院都被人满为患的时候，儿科病房却相对平稳。不知为何，孩子们在这场最严重的疾病中被保护了。

Data collected by the US Centers for Disease Control and Prevention from hospitals across the country suggest that people under the age of 18 have accounted for less than 2% of hospitalizations due to COVID-19 — a total of 3,649 children between March 2020 and late August 2021.

US疾控中心公布的从2020年3月到2021年8月底全国医院总计3649名儿童的数据表明，年龄在18岁以下，因为COVID-19住院治疗的人数不超过2%。

Some children do get very sick, and more than 420 have died in the United States, but the majority of those with severe illness have been adults — a trend that has been borne out in many parts of the world.

有一些孩子病情确实很严重，而且全美有超过420名儿童死亡，但是大多数重症患者是成年人，并且在世界上很多地区都有这个趋势。

This makes SARS-CoV-2 somewhat anomalous. For most other viruses, from influenza to respiratory syncytial virus, young children and older adults are typically the most vulnerable; the risk of bad outcomes by age can be represented by a U-shaped curve. But with COVID-19, the younger end of that curve is largely chopped off.

这一点和 SARS-CoV-2相反。对大多数病毒来说，从流感到呼吸道病毒，幼儿和老年人是典型的易感染人群，重症风险和年纪关系可通过U型曲线来表示。但是对于COVID-19，幼儿的曲线被大大的砍掉了。（好难翻译啊，大概就是年纪和重症风险在二维坐标系上是U型曲线，但是在新冠上，U型的左边，即幼儿的部分，曲线被画平了，那不就是y≈x²，大概这样的吧。）

It’s “absolutely remarkable”, says Kawsar Talaat, an infectious-disease physician at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland. “One of the few silver linings of this pandemic is that children are relatively spared.”

位于马里兰Baltimore 约翰霍普金斯大学彭博公共卫生学院传染病医生 Kawsar Talaat说：“太反常了。这场疫情唯一的一点慰藉是，孩子们相对幸免。”

The phenomenon was not entirely surprising to immunologists, however. With other viruses, adults have the advantage of experience. Through prior infection or vaccination, their immune systems have been trained to deal with similar-looking pathogens.

然而，这种现象对免疫学家来说不足为奇。成人在其他的病毒上有经验的优势，通过既往感染或者疫苗，成人免疫系统被训练能对抗相似的病原体。

The novelty of SARS-CoV-2 levelled the playing field, and showed that children are naturally better at controlling viral infections.

SARS-CoV-2的新颖性和运动性？传播性？同等，同时也表明了儿童天生能更好的控制病毒感染。

“We always think of children as germ factories,” says Dusan Bogunovic, an immunologist and geneticist at the Icahn School of Medicine at Mount Sinai, in New York City. But it’s not because their immune systems are ineffective; they’re just inexperienced, he says.

“我们一般把儿童当成细菌工厂”，免疫学兼遗传学家Dusan Bogunovic（头衔就省了，太长了。）说：“这倒并不是因为他们的免疫系统无效，是因为免疫系统没有任何经验。”

Research is beginning to reveal that the reason children have fared well against COVID-19 could lie in the innate immune response — the body’s crude but swift reaction to pathogens.

研究开始展示了儿童在应对COVID-19上表现更好的原因可能是天生的免疫反应--身体应对病原体天然又迅速的反应。

pathogens：病原体

Kids seem to have an innate response that’s “revved up and ready to go”, says Herold. But she adds that more studies are needed to fully support that hypothesis.

孩子们似乎有天生的反应，即“做好准备随时出击”，Herold说。但是她补充道，还需要更多的研究来完全支持这个假设。

revved up：做好准备的

The emergence of the Delta variant has made finding answers more urgent. Reports suggest that in the United States and elsewhere, children are starting to make up a larger proportion of reported infections and hospitalizations. These trends might be due to Delta’s high transmission rate and the fact that many adults are now protected by vaccines.

德尔塔变异病株的出现使得寻找答案更加紧迫。调查显示，在全美及其他地区，报道的儿童感染和住院率开始变得更高。这种趋势可能是因为德尔塔病株有更高的传染率，而且许多成人注射了疫苗。

For now, there is no clear evidence that children are more vulnerable to or more affected by Delta compared with earlier variants. But SARS-CoV-2, like all viruses, is constantly mutating and becoming better at evading host defences, and that could make understanding childhood’s protective benefits more important. “We haven’t paid much attention to age-related differences in immune responses because it hasn’t had huge clinical implications previously,” says Lael Yonker, a paediatric pulmonologist at Massachusetts General Hospital in Boston. “COVID-19 highlights that we need to better understand these differences.”

到目前为止，没有明确的证据显示，和之前的变体相比，儿童对德尔塔病毒更易感染或更易受到影响。但是SARS-CoV-2，和所有病毒类似，不断突变以更好的躲避宿主的防御，这也许可以理解童年的保护尤其重要。“我们还没有在与年龄相关的免疫反应差异上花太多的注意力，因为它没有太大的临床意义，”Lael Yonker（头衔略）说，“COVID-19提醒我们需要更好的去理解这些差异。”

Brainstorming ideas

Why are children better than adults at controlling SARS-CoV-2? At first, researchers thought that children were simply not getting infected as often. But the data show that they are — at least nearly (children under age ten might be slightly less susceptible).

为什么儿童比成人能更好的防控SARS-CoV-2？一开始，研究人员认为儿童仅仅是和以往一样不受感染。但是，数据表明他们---至少几乎（儿童在10岁以下可能稍微不易感染）。

The American Academy of Pediatrics found that, up until late last month, some 15% of all COVID-19 cases in the United States had been in individuals aged under 21 — that’s more than 4.8 million young people (see ‘Young and infected’). And a survey in India that tested people for antibodies against SARS-CoV-2, which are produced after infection or vaccination, found that more than half of children aged 6–17 — and two-thirds of the population overall — had detectable antibodies.

美国儿科学会发现，直到上个月，在全美COVID-19案例中有15%的确诊人数年纪在21岁以下----那是超过480万年轻人。一项在印度的调查，检测人们在感染或者注射疫苗后产生的SARS-CoV-2抗体，发现有过半的年纪在6-17岁的儿童，总共有三分之二的人群，检测出了抗体。

Source: American Academy of Pediatrics and the Children’s Hospital Association

Clearly, children are getting infected. So maybe the virus can’t replicate in them as well as it does in adults. Some researchers proposed that children might have fewer ACE2 receptors, which the virus uses to enter and infect cells. There is conflicting evidence on age-related differences in ACE2 expression in the nose and lungs, but scientists who measured the ‘viral load’ — the concentration of viral particles — in people’s upper airways have seen no clear difference between children and adults.

很明显，儿童也在感染。可能病毒不能像在成人体内那样复制自己。一些研究人员提出，儿童的ACE2受体可能少一些，病毒可以利用它进入并感染细胞。在与年纪相关的鼻子和肺部的ACE2表现差异上存在相互矛盾的证据，但是检测病毒载量的科学家----主要关注点在病毒颗粒----在儿童和成人的上呼吸道没有发现明显的差异。

In one analysis of 110 children, posted as a preprint on 3 June, researchers found that infants through to teenagers could have high viral loads, especially soon after being infected. “Not only is the virus there and detectable, but it’s live virus,” which means these individuals are also infectious, says Yonker, who led the study.

发表在6月3日的预印本上的一项关于110名儿童的分析中，研究人员发现婴幼儿到青少年都可能有较高的病毒载量，尤其是在感染不久后。领导这项研究的Yonker说：“不仅仅是那些病毒在那里而且可以检测到，并且是活性病毒，这意味着这些个体也是具有传染性的。”

Another proposal is that children, who seem to be sniffling all year round, might be more exposed to other coronaviruses that cause the common cold, and therefore have a squad of antibodies at the ready with some ability to latch on to the pandemic coronavirus. But the weight of evidence suggests that adults also have this immunity. Strikingly, these ‘cross-reactive’ antibodies don’t offer any special protection — if anything, they could lead to a misguided response.

另一种提议是，儿童一年到头都在擤鼻子，更容易暴露在造成普通感冒的冠状病毒中，也因此有一系列的抗体有能力随时做好准备去对抗流行性冠状病毒。但是，大量的证据表明成人也有这种免疫力。引人注意地是，这些交叉反应抗体不能提供任何特殊的保护，更有可能的是，甚至会导致错误的反应。

weight：这里是大量的意思，不是比重。

if anything：总之，更可能的是

Having largely discounted these hypotheses, Herold and her colleagues set out to look at whether there was something specific in children’s immune response that gave them a benefit.

通过大量的否定这些假设，Herold和她的同事开始研究儿童的免疫反应是否有一些特别的东西能给他们带来益处。

Some clues were circulating in the blood of those who have been infected. In a study4 comparing 65 individuals aged under 24 with 60 older people, Herold and her colleagues found that, overall, the younger patients (who had milder symptoms) produced similar levels of antibodies to the older cohort.

有一些线索在那些感染过的人群的血液中。在一个对比了65名24岁以下和60岁老年人的研究中，Herold和她的同事发现，总体上年轻的患者（轻症患者）和老年人产生了同等水平的抗体。

But they had reduced levels of specialized antibodies and cells related to the adaptive immune response, the arm of the immune system that learns about a pathogen and helps to quickly quash it if it ever returns. Specifically, kids had lower levels of ‘neutralizing’ antibodies that block SARS-CoV-2 from infecting cells; antibodies that label infected cells to be gobbled up and destroyed by other cells; and white blood cells known as regulatory and helper T cells.

但是他们降低了和适应性免疫反应相关的特殊抗体和细胞的水平，作为免疫系统的左膀右臂，学会了解病原体，当他们再次到来时可以帮助快速消灭它。尤其注意的是，儿童有更低的阻碍SARS-CoV-2 感染细胞的‘中和’抗体水平，抗体标记感染细胞以便其他细胞吞噬和破坏，白细胞被称作协调性T细胞和辅助性T细胞。

By contrast, the children in the study had higher levels of the signalling proteins interferon-γ and interleukin-17, which alert the immune system to the arrival of a pathogen.

相反，研究中儿童拥有更高的警告免疫系统有病原体的信号蛋白干扰素-γ和白细胞介素-17水平。

These were probably produced by cells that line the airways, and are involved in mediating innate immunity.

这些可能是由呼吸道细胞产生的，同时也参与到先天免疫反应中。

Herold suspected that the children mounted a less robust adaptive immune response because their innate response was more efficient at eliminating the threat.

Herhold怀疑儿童的免疫反应不是太稳固，因为他们的自身反应对消灭威胁十分有效。

An overactive adaptive response in adults, she says, could be causing some of the complications in COVID-19.

成年人中，一种过度活跃的适应性反应可能会造成一些COVID-19的并发症。

Another study5, by researchers in Hong Kong, of adults and children infected with SARS-CoV-2 also found that the adaptive response — specifically that of T-cells — was less potent in children, suggesting that something was happening early on that triggered the difference, says study co-author Sophie Valkenburg at the University of Hong Kong.

香港的研究人员在另一项研究感染SARS-CoV-2的成年人和儿童中也发现了这种适应性反应，尤其是那些T细胞，在儿童身上作用很少，表明早期发生了什么事导致了这些差异，XXXX说。

But, she says, other factors such as reduced inflammation and a more targeted adaptive response could also be important.

但是，她说，其他比如降低炎症和更多目标自适应性反应的因素同样也很重要。

The researchers found that infected children had lower levels of cells known as monocytes, including inflammatory monocytes, which act as a bridge between the innate and adaptive immune systems. But these children did have higher levels of T follicular helper cells, which are important for making an early antibody response.

研究人员发现，感染的儿童有更低水平的单核细胞，包括作为自身和适应性免疫系统桥梁的炎症单核细胞。但是这些儿童有较高的T滤泡辅助细胞水平，这些对早期的抗体反应很重要。

First responders

Herold and her colleagues have since tried to measure more directly the innate response in children. They took nose and throat swabs from people arriving at the emergency department, including 12 children with milder disease and 27 adults, some of whom died. The children had higher levels of signalling proteins such as interferons and interleukins, and higher expression of the genes that code for such proteins2.

Herold和同事们也曾尝试去测量儿童更直接的自身反应。他们从急诊室采集了轻症12名儿童和27名成人的鼻咽拭子，他们其中有一些人已经过世了。儿童有更高的例如干扰素和中间蛋白的信号蛋白水平，还有较高的对这种蛋白编码的基因数量。

One broad category of immune cells that could be playing an important part in children, says Yonker, are innate lymphoid cells, which are among the first to detect tissue damage and secrete signalling proteins that help to regulate the innate and adaptive immune responses.

一种广泛分类的免疫细胞可能在儿童体内起了重要作用，就是先天淋巴细胞，一种最先检测到组织损伤并分泌信号蛋白以帮助调节自身和自适应免疫反应。

In one study6 posted as a preprint on 4 July, Yonker and her colleagues found that the number of innate lymphoid cells in the blood of people who did not have COVID-19 declined with age and was lower in men — mirroring the greater risk of severe disease observed in older men.

发表在7月4日的预印本上的一项研究，Yonker和她的同事们发现血液中的先天淋巴细胞在没有感染COVID-19的人群中随着年龄降低，在男性中中较低。也反映了老年男性患重症的风险更大。

Adults with severe disease and children with symptoms also had reduced levels of these cells.

重症的成年人和有症状的儿童这些细胞的水平也降低了。

Compared with adults, children recently infected with SARS-CoV-2 have also been found to have higher levels of activated neutrophils, cells that are on the front line in the response to unfamiliar invaders7. Neutrophils ingest viral particles before they have a chance to replicate, says Melanie Neeland, an immunologist at the Murdoch Children’s Research Institute (MCRI) in Melbourne, who led the work. Furthermore, they become less effective with age.

和成年人相比，近期感染 SARS-CoV-2的儿童也被发现有更高的活跃中性粒白细胞水平，一种对抗不熟悉的入侵者时首先做出反应的细胞。中性粒白细胞在他们复制之前摄取病毒颗粒，此外，他们随着年纪的增长效果会下降。

Epithelial cells that line the insides of the nose could also be coordinating the quick response.

鼻子内的上皮细胞也可能参与到这种快速反应中。

In children, these cells are flush with receptors that can recognize molecules commonly found in pathogens; specifically, researchers have found that children have significantly higher expression of genes encoding MDA5, a receptor known to recognize SARS-CoV-2, than do adults.

在儿童中，这些细胞充满了能识别病原体中的常见分子的受体，特别是研究人员发现儿童比成年人有明显较高的一种被称为识别SARS-CoV-2的编码MDA5的基因表达。

After spotting the viral intruder, these cells immediately trigger the production of interferons.

发现病毒入侵后，这些细胞立刻触发干扰素的产生。

“For us adults, it takes two days to ramp up the viral defence system to a level that we see from day zero with children,” says study co-author Roland Eils, a scientist in computational genomics at the Berlin Institute of Health. “It’s the time lag which makes the difference between children and adults.”

“对于我们成年人来说，将病毒防护系统提升到一个水平需要花费两天的时间，儿童却只需要不到一天。这种成人和儿童间的差异是时间延迟造成的。”Roland Eils说。

这段完全不了解啥子意思，that we see from day zero with children 和 time lag 不晓得怎么翻译。

Studies of rare, inherited, immune disorders also point to a predominant role for innate immunity in thwarting respiratory pathogens such as influenza.

对罕见、遗传免疫疾病研究也指出，自身免疫在抑制流感类呼吸病原体起主导作用。

Isabelle Meyts, a paediatric immunologist and physician at the Catholic University of Leuven in Belgium, regularly sees children with immune disorders. When the pandemic hit, she prepared a plan to protect them. “The patients I was most scared for were actually the patients who have innate immune defects,” says Meyts.

Isabelle Meyts定期看患有免疫疾病的儿童。当疫情来的时候她准备了一个方案去保护他们。“我真正害怕的病人，是那些有先天免疫缺陷的病人。”

Her hunch has so far proved correct. Children with disorders affecting their adaptive immune response — those who don’t produce antibodies or have faulty B-cell and T-cell production, for example — did not encounter problems when infected with SARS-CoV-2.

她的直觉已经被证明是正确的。患有疾病的儿童会影响他们的自适应免疫反应，他们不能产生抗体或者产生有缺陷的B细胞和T细胞，比如，当感染SARS-CoV-2不会遇到问题。（应该是说会感染上SARS-CoV-2吧，越来越难了。）

Among those that became severely ill were children with shortcomings in their innate immune response, she says. “It’s not really the adaptive immune system that is helping you to beat this virus.”

在那些自身免疫反应有缺陷的儿童中发展成重症，她说：“实际上也不是自适应免疫系统在帮你对抗病毒。”

A study in adults also found that a small number of people with severe COVID-19 have mutations that disrupt type 1 interferon activity, which plays a part in the innate immune response to viruses.

一项成人的研究中也发现，一小部分感染了COVID-19重症患者中有感染1型干扰素活动的变体，这种干扰素在对抗病毒的先天免疫反应中发挥作用。

Separate analyses found that one in ten people with life-threatening COVID-19 produced antibodies that blocked the activity of these interferons, and that the prevalence of such antibodies increases with age in people who have not previously been infected with the coronavirus.

单独的分析发现影响生命的COVID-19重症患者有十分之一产生了阻碍这些干扰素活动的抗体，这种抗体的流行率在那些之前没有感染过冠状病毒的人中随着年纪增加。

But, an overactive innate response might be detrimental as well. People with Down’s syndrome, for example, are more at risk of severe COVID-19, which Meyts says could be because the extra chromosome they have contains several genes involved in the type 1 interferon response. There is an intriguing balance to be struck between a deficient initial response and an excessive one, says Meyts. “It needs to be exactly right on the spot, and the timing needs to be perfect.”

但是，过度的先天反应也可能不利。比如，患有唐氏综合征的人，有更高的重症风险，可能是因为他们包含的多余的染色体上有一些参与到1型干扰素反应的基因。在初始反应不足和过度反应之间有一个有趣的平衡。它需要恰好在一个点上，时间也需要刚刚好。

Tickling bad memories

Innate immunity is hardly the whole story, say researchers, especially given how interconnected it is with the adaptive response.

研究人员说，自身免疫不是全部的问题，尤其是考虑到他和适应性反应的内部联系。

“The idea that the immunologic tone is different in children seems likely,” says Laura Vella, an immunologist and paediatric infectious-diseases researcher at the Children’s Hospital of Philadelphia, Pennsylvania. “But what’s contributing to that difference?” It could be many things working together, she says.

“关于儿童的免疫张力差异的观点似乎是有可能的，”Laura Vella说。“但是，是什么造成了这种差异呢？”可能是多种原因共同造成的。她说。

Some researchers propose that years of exposure to other human coronaviruses could mean that adult immune systems approach SARS-CoV-2 the way they would those other viruses, resulting in a less effective response — a concept known as 7. By contrast, kids could be producing a fresh, more finely tuned response to a brand-new virus.

一些研究人员提出了一种抗原原罪说，即多年暴露在人类其他冠状病毒中可能意味着成年人的免疫系统会像接近其他病毒一样对抗SARS-CoV-2，这就导致了更低效的反应。相反，儿童可能会产生一个针对新病毒的全新的更精细的反应。

Amy Chung, an immunologist at the Peter Doherty Institute for Infection and Immunity in Melbourne, Australia, has seen some evidence of this in an expansive study of antibodies in the blood of a few hundred children and adults, including 50 infected with SARS-CoV-2. She and her colleagues found that adults had more cross-reactive antibodies targeted at parts of SARS-CoV-2 that were similar to bits of other coronaviruses, whereas children tended to produce a broader range of antibodies against all sections of the virus.

免疫学家Amy Chung在一项对几百个儿童和成人血液中的抗体的广泛研究中，发现了一些证据，其中包括感染了SARS-CoV-2的50人。她和同事们发现，成年人有更多的针对SARS-CoV-2部分的交叉反应抗体，这部分和冠状病毒相似。与此同时，儿童更倾向于产生更大范围的对抗病毒所有部分的抗体。

Researchers are also looking at other factors that are known to worsen with age, such as the ability to control inflammation and heal damaged tissue. Children are less prone to clots forming in blood vessels, and this could offer some protection, says Vera Ignjatovic, a biochemist who studies paediatric haematology at the MCRI.

研究人员也在寻找其他已知的随着年纪增长而恶化的因素，比如控制炎症和自愈组织损伤自愈的能力。“儿童不太容易形成血凝块，这可能也提供了一些保护，”生化学家Vera Ignjatovic说。

Of course, not all children have asymptomatic or mild infection. Some, many of whom have underlying conditions such as chronic heart disease or cancer, get serious pneumonia.

当然，不是所有的孩子都是无症状或者轻症。有一些有基础疾病的，比如慢性心脏病或者肿瘤，会造成严重的肺炎。

And estimates vary widely for the prevalence of ‘long COVID’, in which symptoms persist for months or more.

对长期新冠病毒流行率的估计差异很大，即症状持续数月或者更久。

A recent preprint suggested that up to 14% of young people who test positive for COVID-19 have multiple symptoms three months after the diagnosis.

一项近期的预发行本表明，有高达14%的年轻人检测出阳性三个月后出现多种症状。

And a small group of otherwise healthy children — some 3 out of 10,000 infected individuals aged under 21 — experience a condition known as multi-system inflammatory syndrome in children (MIS-C).

一小部分原本健康的孩子---万分之三感染个体在21岁以下，经历了一种被称为多系统炎症综合征的情况。

They generally respond well to the initial infection, but about a month later are admitted to hospital with a host of symptoms, from heart failure to abdominal pain and conjunctivitis, with minimal damage to the lungs. “It’s a sick group of kids,” says Vella.

他们一开始对初期症状反应良好，但是一个月后就因为一系列的并发症入院，从心脏衰竭到腹部疼痛及结膜炎，对肺部的损害最小。Vella说，这是一群生病的孩子。？？？？

Michael Levin, a paediatrician and infectious-diseases physician at Imperial College London, thinks MIS-C is probably the result of an outsized antibody or T-cell reaction to the infection. But despite hundreds of papers on the topic, “exactly what distinguishes children who get MIS-C from the rest of the child population is completely unknown”, says Levin.

XXXX的儿科兼传染病医生Levin认为， MIS-C可能是感染后抗体或者T细胞过大的结果。“尽管有数百篇关于这个话题的论文，获得MIS-C的儿童和其他儿童的区别到底在哪里还是未知的。” Levin说。

As the pandemic wears on, researchers worry that the virus could evolve in ways that thwart some part of kids’ innate protection.

随着疫情的传播，研究人员担心病毒会以某种方式进化，可能会阻碍儿童的先天保护。

Some researchers have found that the Alpha variant, which was dominant in some parts of the world for a time, developed tricks that allowed it to suppress the body’s innate immune response.

一些研究人员发现一度在世界上部分地区占主导的α病毒，进化出了可以抑制自身免疫反应的能力。

They worry that Delta could do the same. For now, increased hospitalizations of children in regions where Delta is circulating seem to be the result of its enhanced infectivity across all ages, coupled with the fact that many adults are vaccinated or have already been infected with SARS-CoV-2. But researchers are watching carefully.

他们担心德尔塔病株也会这样进化。目前，在德尔塔传播的地区的儿童住院人数在增加，似乎是它在全年龄段增强的传染性导致的，再加上许多成人已经注射疫苗或者已经被SARS-CoV-2感染过的事实。

“Almost all viruses have developed ways of evading the innate immune system, and COVID-19 is no exception to that rule,” says Herold. “Right now — knock on wood — the kids are still winning with their innate immunity.” But for how much longer? “We don’t know.”

“几乎所有的病毒都会进化以躲避天生的免疫系统，COVID-19也不例外。幸好当前孩子们的先天免疫力占上风，但是又能持续多久呢？我们也不知道。”Herhold说。