对新冠疫情的监测发现，儿童的发病率较低，症状也较轻。这是为什么呢？科学家认为，这可能是因为儿童经常得感冒，免疫系统已经做好了充分准备。
Children may be protected from coronavirus because they catch so many colds, scientists have suggested.
科学家指出，儿童经常感冒可能会保护他们免受新冠病毒的伤害。
Figures from the Office for National Statistics (ONS) suggest children are just as likely to pick up the virus, but few ever develop serious disease, or even show symptoms.
英国国家统计局的数据显示，儿童和大人一样容易感染新冠病毒，但是发展成重症的儿童没有多少，有些甚至没有表现出症状。
Now scientists have suggested that children may be resistant because their immune systems are already well primed by the common cold.
现在科学家指出，儿童对新冠病毒可能有抵抗力，因为普通感冒已经让他们的免疫系统做好了充分准备。
The common cold is caused by four different types of coronavirus which circulate in the community and are largely harmless. But while adults pick up a cold around two to four times a year, school age children catch an average of 12 colds annually, studies have shown.
普通感冒是由社区中流行的四种不同的冠状病毒引起的，大部分都是无害的。但是研究显示，成年人每年大约感冒两到四次，学龄儿童每年平均感冒12次。
Professor Sir John Bell, Regius Professor of Medicine, University of Oxford told the House of Lords Science and Technology Select Committee, that it may allow youngsters to build up some ongoing resistance that adults do not have.
牛津大学医药学钦定讲座教授约翰·贝尔爵士告诉上议院科学技术特别委员会说，这可能会让儿童建立起成年人没有的抵抗力。
“How you respond may be due to the state of your existing immunity to coronaviruses generally,” he told peers.
他告诉同行说：“你对病毒的反应可能要归因于你对冠状病毒群体的现有免疫力状况。”
“There is an interesting speculation at the moment, that suggests that many people in young or middle aged groups may have T-cells that can already see coronavirus. It may well be able to provide some protection against this pathogen when it arrives.
“现在有一种有趣的猜测，就是许多年轻人或中年人可能拥有接触过冠状病毒的T淋巴细胞。当人体感染冠状病毒后，这种细胞很可能会保护人体不受病原体侵害。”
“A lot of kids get seasonal coronaviruses and it’s pretty common in our population and many will have quite a strong immunity to coronaviruses generally.
“很多孩子都会感染季节性冠状病毒，这种病毒在我们的人口中相当普遍，许多人对冠状病毒群体都已拥有相当强的免疫力。”
“That is unproven, but there is evidence now for cross-reactivity at T-cell level at least, and that well might help dampen the effects of the virus when we get it.”
“这还没有经过证实，但是现在有证据表明病毒至少在T淋巴细胞层面会发生交叉反应，这会在感染时降低病毒的危害性。”
Studies have shown that by the age of four, some 70 percent of children already have antibodies against seasonal coronavirus, which could offer important protection.
过去的研究显示，大约70%的儿童在四岁前已经对季节性冠状病毒拥有抗体，该抗体能提供重要的保护作用。
Professor Adrian Hayday, Chair, Department of Immunobiology, King's College London said the immune systems of young people may simply be better at reacting to new viruses.
伦敦国王学院免疫生物学部主任阿德里安·黑戴教授表示， 年轻人的免疫系统可能就是更善于应对新病毒。
“All adults past a certain age - 30 to 35 - eventually have no thymus so their T-cells work by looking at whether they have seen something before, whereas children are very good at seeing things that are completely unknown.
“所有超过一定年龄——30到35岁——的成年人最后胸腺组织都会消失，所以他们的T淋巴细胞是否发挥作用取决于他们是否感染过这种病毒，而孩子们的T淋巴细胞则非常善于应对完全陌生的病毒。”
The scientists also said that older people may suffer from immune cell ‘senescence’ where their immune cells start to shut down but are not cleared away and replaced with a working version.
科学家还表示，老年人可能遭受了免疫细胞的“老化”，他们的免疫细胞开始停工，但却没有被清除，也没有能工作的免疫细胞来替代。
senescence[sɪˈnesns]: n. 衰老
But Prof Bell said for most people coronavirus was not a serious illness.
但是贝尔教授说，对于大多数人而言新冠病毒不会发展成重病。
“The people who get severe disease and die, the vast majority are elderly people and when young people get this disease they tend not to suffer very much.
“发展成重症而死亡的绝大多数人都是老年人，如果年轻人感染了病毒，他们一般都不会太严重。”
“That might be the state of people’s immune system at different ages. 70 percent of the people who get this are completely asymptomatic, so at one end of the spectrum this is not a bad viral disease, at the other end it’s terrible.
“这可能是因为人的免疫系统在不同年龄的状态不一样。感染新冠病毒的人有70%完全没有症状，因此从一边来看这不是一种很糟糕的病毒性疾病，但从另一边来看这个病非常危险。”
“The vast majority of people who get this disease don’t even know they’ve had it.”
“绝大多数感染病毒的人甚至都不知道自己已经感染上了。”