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All this suggests that the number of infected people unwittingly infecting others could be quite large.
所有這些都表明，被感染者的人數可能相當龐大。
What is unclear is how infectious these people actually are.
現在還不清楚這些人到底有多大的傳染性。
That is what the second strand of research on the asymptomatic and presymptomatic transmission of SARS-COV-2 deals with.
這是關于SARS-COV-2無癥狀和癥狀前傳染的第二部分研究。
It draws on various laboratory studies.
它利用了各種實驗室研究。
In several of these the amount of the virus in nasal and throat swabs taken from infected people
在其中幾個研究中，從無癥狀感染者鼻腔和咽喉拭子中采集的病毒量
who were presenting no symptoms at the time was similar to the amount found in those who had symptoms.
和那些有癥狀的人的病毒量相似。
Indeed, for those who do go on to develop symptoms, the amount of virus they have in them peaks close to the onset of those symptoms,
確實，對于那些繼續出現癥狀的人來說，他們體內的病毒數量在這些癥狀出現之前達到頂峰，
which suggests that it may be easily transmissible at an early stage of infection.
這表明在感染的早期階段，它可能極易傳播。
As a persistent cough is a common symptom, it might be expected that those who are symptomatic are more effective in spreading the virus than those who are not.
持續的咳嗽是一種常見的癥狀，因此有癥狀的人比沒有癥狀的人更能有效地傳播病毒。
Contrariwise, however, those with symptoms often feel unwell and take to their beds.
但相反，那些有癥狀的病人通常會因為不舒服而臥床休息。
They are, therefore, coughing mainly onto their sheets and blankets rather than onto strangers in the street.
因此，他們主要是對著床單和毯子咳嗽，而不是對著街上的陌生人。
The third strand of research into the question of silent spreading is mathematical modelling.
關于寂靜傳染問題研究的第三部分是數學建模。
One such study was published in Science on March 31st by Luca Ferretti of Oxford University and his colleagues.
牛津大學的Luca Ferretti和他的同事在3月31日的《科學》雜志上發表了一項這樣的研究。
It used data on 40 infected people for whom the source of their infection was known with high probability,
該研究40名感染患者的數據，這些患者的感染源基本已知，
and the timing of their symptoms and those of the people who infected them was well documented.
而且他們出現癥狀的時間和感染他們的人都有詳細的記錄。
The researchers estimate that between a third and a half of transmission occurs from people who are without symptoms at that point—
研究人員估計，三分之一到二分之一的傳染發生在當時沒有癥狀的人身上——
a result which broadly agrees with estimates from similar studies by others.
這一結果與其他類似研究得出的估計大致一致。
Collectively, all this research may help explain why SARS-COV-2 has spread with such ferocity.
總的來說，所有這些研究可能有助于解釋為什么SARS-COV-2傳播地如此兇猛。
But the study, in particular, of those who are infected but never present symptoms is also crucial to understanding how that spread may ebb—
但這項研究，特別是對那些無癥狀感染者的研究，對理解這種傳播將如何減弱也至關重要——
for the pool of those who have been infected and are, therefore, immune to reinfection at least in the short term also includes these people.
因為這些患者也屬于因被感染而對再次感染有短期免疫的人群。
Pandemics end when the pathogen causing them runs out of individuals to infect. Some of those susceptible will have died.
當引起流行病的病原體沒有足夠的個體可以感染時，流行病就結束了。其中一些易感者將會死亡。
Enough of the rest would then be immune for the population to have developed "herd immunity".
剩下的人就獲得免疫力，從而形成“群體免疫”。
In the case of the current pandemic of SARS-COV-2, the more silent infections there have been, the faster this herd immunity will arrive.
在當前SARS-COV-2大流行的情況下，寂靜傳染病例越多，這種群體免疫到來得越快。
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