A lot of didn't get sick from it now, and we got sick from it before.

许多人不会再因为微生物得病了,而人们以前则会因此生病

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