If you're trying to prevent a disease that only occurs at a rate of 20 per 100,000 people you have to give the vaccine to millions in order to see if the number goes down.

如果你尝试去防治一个,发病概率为十万分之二十人的疾病,那么就必须将疫苗分发给数百万人,以观察疫苗能否降低发病率

耶鲁公开课 - 生物医学工程探索课程节选

So, you're treating healthy people and you're trying to prevent them from getting a disease and you don't know who's going to get it.

所以,你处治的对象是健康人群,要使他们远离疾病,但你不知道谁会被感染

耶鲁公开课 - 生物医学工程探索课程节选

As we'll see in section today, a vaccine does not have to be totally perfect in order to prevent transmission of a disease, because when a disease enters a community its spread from one person to another.

有如我们今天看到的,疫苗不一定非要,绝对完美地阻止疾病的传播,因为当疾病侵入一个社区后,会在人群间传播

耶鲁公开课 - 生物医学工程探索课程节选