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Guidance for health-care workers is, therefore, clear: wear masks. Advice for members of the public has been more variable.
因此，對醫護工作者的指導方針很明確：戴口罩。對公眾的建議則更加多變。
Since the start of the outbreak the WHO and the CDC have advised people to avoid the use of masks
自疫情爆發以來，WHO和CDC就建議大家不要使用口罩，
unless they are in direct contact with symptomatic covid-19 patients. This is because such masks are a scarce resource.
除非他們和有癥狀的covid-19病患有直接接觸。這是因為這類口罩是一種稀缺資源。
At the end of February Jerome Adams, America's surgeon-general, beseeched his fellow citizens on Twitter to "seriously people—STOP BUYING MASKS!"
二月底，美國衛生部長杰羅姆·亞當斯在推特上懇求他的同胞們“嚴肅點——不要再買口罩了!”
because a run on them might cause supply problems for health-care workers.
因為對它們的持續購買可能會導致醫護工作者的口罩供應問題。
A month or so later, the advice seems to be changing. The CDC now encourages the populace to wear homemade coverings for their mouths and noses.
大約一個月后，這個建議似乎改變了。CDC現在鼓勵民眾戴自制的口罩。
Dr Adams himself starred in an official video demonstrating how to use rubber bands around folded pieces of cloth to make DIY masks.
亞當斯醫生本人在一段官方視頻中擔任主角，演示如何用橡皮筋纏在折疊的布片上自制面具。
Recently, the Czech Republic and Slovakia started requiring anyone stepping out into certain public places to use nose and mouth coverings.
最近，捷克共和國和斯洛伐克開始要求任何進入某些公共場所的人都要遮住自己的鼻子和嘴巴。
The same rule applies in Lombardy, in northern Italy, which was the centre of the covid-19 outbreak in that country.
意大利北部的倫巴第也采取了同樣規定，那里是該國covid-19疫情的中心。
And Austria now requires masks in places such as supermarkets and pharmacies.
奧地利現在要求在超市和藥店等地方戴口罩。
The changing advice is testament to an evolving understanding of SARS-COV-2 itself,
不斷變化的建議證明了對SARS-COV-2本身的不斷的理解，
and also to continuing debate among scientists about how far previous research on the effectiveness of masks can usefully be brought to bear on the current crisis.
也證明了科學家們對以往關于口罩有效性的研究在多大程度上能夠有效地應對當前危機的爭論仍在繼續。
It might seem intuitively obvious that having people cover their noses and mouths in public would be useful.
讓人們在公共場合捂住鼻子和嘴似乎是很有用的。
In fact, the science of the matter is not clear-cut.
事實上，這個問題的科學依據并不明確。
Extrapolating to the laity the research which shows that masks and respirators are effective for those who work in health care is actually problematic.
表明口罩和防毒面具對那些在醫護工作者是有效的研究實際上是有問題的。
One reason is that doctors and nurses are better-trained than others in how to wear these devices.
一個原因是醫生和護士在如何佩戴這些設備方面比其他人更專業。
For example, surgical masks work less well when they become moist, and so need to be replaced regularly throughout the day.
例如，當口罩變得潮濕時，效果就不太好了，因此需要在一天中定期更換口罩。
Health-care workers will do this routinely. A member of the public might not.
這是醫護工作者常規做法。公眾可能不會。
As to N95 respirators, they are notoriously difficult to fit in a way that seals them properly to a user's face.
至于N95口罩，它們是出了名的難戴，很難把它們正確地密封在使用者的臉上。
Yet not fitting them correctly can negate their benefits—as can touching the front of a mask, or taking it off in the wrong way and so contaminating your hands.
然而，錯誤的佩戴可能會抵消它們的好處——就像觸摸口罩的正面，或以錯誤的方式摘下口罩，從而污染你的雙手一樣。
Nor do masks and respirators protect people's eyes from virus particles. Only close-fitting goggles can do that.
口罩和防毒面具也不能保護人們的眼睛免受病毒顆粒的侵害。只有貼身的護目鏡才能做到這一點。
Finally, as Susan Michie, a health psychologist at University College London, observes, people might feel a false sense of security when wearing masks,
最后，倫敦大學學院的的健康心理學家Susan Michie觀察到，人們戴口罩時可能會產生一種虛假的安全感，
and thus pay less attention to other important behaviours such as social distancing and handwashing.
從而對社交距離和洗手等其他重要行為關注較少。
This does not, of course, show that masks for the public are of no use. A better way to think about them in this context might be that,
當然，這并不能說明公眾戴口罩是沒有用的。在這種情況下，更好的思考方法可能是，
rather than helping healthy people shield themselves from infection,
與其幫助健康的人保護自己免受感染，
they could be used to stop those who are already infected broadcasting the virus into the air around them.
不如用口罩來阻止那些已經感染病毒的人向周圍的空氣傳播病毒。
Given that much transmission of SARS-COV-2 is suspected to occur before someone who has the virus actually shows any symptoms,
鑒于我們懷疑SARS-COV-2的大量傳播是發生在患者真正表現出任何癥狀之前，
encouraging everyone to wear masks in public regardless of whether they are symptomatic could be a useful way to break the chain of transmission.
因此鼓勵所有人在公共場合戴口罩，不管他們是否有癥狀，這可能是打破病毒傳播鏈條的一種有效方法。
A study published in the current edition of Nature Medicine backs this idea up.
發表在最新一期《自然醫學》期刊雜志上的一項研究支持了這一觀點。
Ben Cowling, an epidemiologist at Hong Kong University, measured the amount of virus shed, in half an hour of breaths and coughs,
香港大學的流行病學家Ben Cowling檢測了參與者在半小時內呼吸和咳嗽中排除的病毒數量，
by participants infected with a variety of respiratory viruses, including influenza, rhinovirus and coronaviruses (though not SARS-COV-2).
這些參與者感染了各種呼吸道病毒，包括流感、鼻病毒和冠狀病毒（雖然不是SARS-COV-2） 。
In the case of those with coronaviruses, 30% of droplets and 40% of aerosol particles exhaled by participants without a surgical face-mask on contained virus particles.
在對冠狀病毒參與者的檢測中，沒有戴醫用口罩的參與者呼出的30%的飛沫和40%的氣溶膠顆粒含有病毒顆粒。
When they wore masks, that dropped to zero.
當他們戴上口罩時，這個數字降為零。
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