从发表在《临床传染病》上的综合研究来看，自1930年确认第一例猪流感传染人类的病例以来，世界上被感染的人只有数十位。

According to a comprehensive study published in the journal Clinical Infectious Diseases, swine flu had infected only several dozen people in the world since it was first identified in 1930.

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感染上禽流感的人类的死亡率是50%，但是迄今为止，被感染的人类大多数是通过与被感染鸟类的直接接触而传染上的。

Death rates for human infected are around 50 percent but, so far, humans have been infected mostly by direct handling with infected birds.

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一旦病毒从动物身上“溢出”到从事相关职业的人身上譬如狩猎，农耕或活禽市场买卖，在相关人员被传染后，病毒开始发威。

These outbreaks will flare up after viruses "spill over" from animals into people with occupations such as hunting, farming or working in live-animal markets.

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Now, the problem, or one of the challenges with clinical trials of vaccines is that you have to enroll a lot of patients into clinical trials because only a few are going to get sick in any case, only 20 out of 100,000.

现在的问题是,这也是疫苗临床试验的挑战之一,临床试验必须包括足够多的病人,毕竟只有一小部分人会被传染,十万人里面只有二十人被传染

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