It dropped dramatically in the period from 1954-- this is these filled black bars refer to this axis, polio cases per 100,000 population dropped down to only three or four cases by 1956.

患病率在一九五四年后的,一段时间里急剧下降,该坐标轴上的这些黑色柱形图表明,到一九五六年,小儿麻痹症的发病率,已经降低至每十万人中仅三到四人发病

耶鲁公开课 - 生物医学工程探索课程节选

was about 20 per 100,000 people.

每十万人中有大约二十人受到感染

耶鲁公开课 - 生物医学工程探索课程节选

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

耶鲁公开课 - 生物医学工程探索课程节选