Scientists seek reason why coronavirus has less impact on children

双语阅读 | 金融时报：科学家研究，新冠肺炎对儿童的影响较小？

The children of China provided the first clue that Covid-19 does not spread its ill-effects equitably across the generations. The young, except those with underlying health conditions, appear to be escaping the worst of this pandemic.

中国的孩子最先展示出，新型冠状病毒肺炎（COVID-19，即2019冠状病毒病）并没有均等地在所有年龄段的人群中传播其严重影响。除了存在基础健康问题的人，年轻人似乎不在此次病毒影响最大的人群之列。

One early study showed that, of more than 700 children known to have close contact with a confirmed case or to live in a recently affected household, only 10 tested positive. Of those children, all under 15 years old, none needed respiratory support or intensive care. A study in the journal Paediatrics, released early and subject to revision, noted one death in more than 2,000 confirmed and suspected child cases.

一项早期研究显示，在逾700名已知与确诊病例有过密切接触、或是家中最近有人确诊感染的儿童中，只有10人新冠病毒检测结果呈阳性。这10名儿童均不满15岁，且没有一人需要呼吸支持或重症监护。一项早期发表在《儿科学》(Paediatrics)杂志上、可能会有修正的研究指出，在逾2000例新冠肺炎确诊和疑似儿童病例中，只有一人死亡。

Now attention is turning to the scientific reasons for the age discrepancy. One UK academic hopes to start a study into whether young lungs lack an appropriate “lock” that can be picked by the virus to gain entry into the body’s respiratory machinery.

现在人们开始关注不同年龄群体存在这种差异的科学原因。英国一位学者希望开展一项研究，探讨年轻人的肺是否缺少一种合适的“锁”，让新冠病毒无法借以进入呼吸系统。

Covid-19 is not the first coronavirus disease to home in on older people: age was also a risk factor in the 2002-03 Sars epidemic. While children and adolescents seemed susceptible to infection, showing symptoms such as fever, cough and vomiting, their illnesses tended to be milder and shorter with, as one paper asserts, no child deaths.

新冠肺炎并不是第一种针对老年人的冠状病毒疾病：在2002-03年间爆发的“非典”(SARS)疫情中，年龄同样是一个风险因素。虽然儿童和青少年似乎易受感染，并表现出发烧、咳嗽和呕吐等症状，但他们往往病情较轻且病程较短，而且正如一篇论文所称，没有儿童因此死亡。

In order to infect an animal or a person, a virus must hijack cell machinery so it can start replicating. That means finding an entry point into cells in the first place. The coronaviruses that cause Sars and Covid-19 share an important feature: they use the same “keyhole” to enter cells, called the ACE2 receptor. The receptors are primed to latch on to the ACE2 protein, which helps to regulate heart and kidney function as well as lung development ( remdesivir, a Sars antiviral that targets ACE2 receptors, is being trialled as a Covid-19 treatment).

为了感染动物或人类，病毒必须要劫持细胞机制，这样它才能开始复制。这意味着，病毒首先需要找到进入细胞的入口。导致“非典”和新冠肺炎的这两种冠状病毒有一个重要的共同特征：它们利用了同样的“锁孔”进入细胞，这个“锁孔”被称为ACE2受体。这些受体可用于附着到ACE2蛋白上——这种蛋白有助于调节心脏和肾脏功能、促进肺部发育。（一种针对ACE2受体的抗“非典”病毒药物瑞德西韦(remdesivir)正作为新冠肺炎治疗药物进行试验。）

Calum Semple, professor of child health and outbreak medicine at Liverpool University, theorises that ACE2 receptors in children’s lungs provide a poor fit for this viral key: “We know that lung development doesn’t finish until the teenage years. My hypothesis, and it is just that, is that ACE2 is highly regulated in lung development. Because of this regulation, the ‘lock’ might be expressed differently in kids’ lungs.”

利物浦大学(Liverpool University)儿童健康与疾病爆发医学教授卡卢姆•森普尔(Calum Semple)推测，儿童肺部的ACE2受体与这种病毒的钥匙无法很好地适配：“我们知道，肺部发育直到青少年时期才会结束。我的假设是——仅仅是假设——ACE2在肺部发育过程中受到高度调控。由于这种调控，儿童肺部‘锁’的形式可能有所不同。”

These cellular locks might also look different in children’s upper and lower airways, and explain why they become infected — and able to transmit Covid-19 — but do not show the same progression to severe symptoms. The virus can only descend so far before being barred.

这些细胞锁在儿童的上呼吸道和下呼吸道中可能也有所不同，这就解释了为什么他们也会被感染——并能传播新冠病毒——但不会发展出严重的症状。新冠病毒在被阻挡之前只能沿着呼吸道有限地向下蔓延。

Prof Semple, who heads the UK’s clinical studies response to emerging infections, has recruited more than 2,500 adult and child Covid-19 patients to test this hypothesis, among others. Studies will also examine other crucial aspects of the pandemic: which treatments work best; why people with underlying health conditions fare poorly; and why men outnumber women in Covid-19 hospital admissions.

森普尔教授是英国应对新发传染病临床研究的负责人，他已经招募了逾2500名成人和儿童新冠肺炎患者来验证这一假设以及其他假设。研究还将验证这场大流行病的其他关键问题：哪种治疗方法效果最好、为什么有基础健康问题的人情况更糟糕、以及为什么因新冠肺炎入院治疗的男性多于女性。

Other researchers suggest children may enjoy some immunity to Covid-19 via cross-exposure to other coronaviruses associated with common colds. Prof Semple disagrees, saying in that case babies, with no prior immunity, would be especially at risk of severe illness, as they are with influenza and respiratory syncytial virus (RSV puts an estimated 3m under-fives in hospital annually). That is not borne out clinically.

其他研究人员表示，儿童可能会通过交叉接触其他与普通感冒相关的冠状病毒，从而对新冠病毒有一定的免疫力。森普尔教授并不认同这种观点，他表示，如果是这样，没有预先免疫力的婴儿会特别容易出现重症，就像他们感染流感和呼吸道合胞病毒(RSV)时一样（RSV每年会导致约300万名5岁以下儿童住院）。这种观点没有得到临床证实。

While babies and children are not succumbing to the same degree as adults, it is a mistake to think they are invincible. The Paediatrics study noted that nearly 6 per cent of child patients in China became severely or critically ill, despite only one death being recorded. The US has reported the first death of an infant with Covid-19, although the exact cause of death has not been confirmed.

虽然婴儿和儿童因新冠肺炎致死的程度不会像成年人那样严重，但认为他们完全不会被这种病毒打倒，也是错误的。《儿科学》的研究指出，尽管只出现了一例死亡病例，但中国近6%的儿童患者病情严重或危重。美国已报告了感染新冠肺炎婴儿的首例死亡，尽管目前尚未证实其确切的死亡原因。

Even if they are rarely victims, children are still generous spreaders. While so much remains unknown about Covid-19, particularly long-term health outcomes, the precautionary principle should continue to govern our response.

虽然很少有儿童感染新冠肺炎，但他们会大量传播这种病毒。尽管目前在新冠肺炎、尤其对其造成的长期健康影响，仍存在许多未知之处，我们仍应继续以预防的原则继续应对病毒。