But vaccines, and particularly in the last hundred years, vaccines have been one of the most important elements in our progress.

但是疫苗,尤其是在近一百年来,疫苗已经成为,感染性疾病防治进程中最重要的一环

耶鲁公开课 - 生物医学工程探索课程节选

So,as the vaccine was passed from arm to arm, it became less potent, and the length of protection that it would give you varied.

所以当疫苗从一个人传给另一个人之后,它的防治效力会减弱,它带给人的免疫期限也会改变

耶鲁公开课 - 生物医学工程探索课程节选

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