We know now that it's caused by a related virus, called vaccinia, remember the virus that causes smallpox is called variola.

我们现在知道这病由一种相关的病毒引起,这种病毒叫牛痘病毒,想想天花病毒也被叫做牛痘病毒

耶鲁公开课 - 生物医学工程探索课程节选

But variola, which causes smallpox in humans, and vaccinia, which causes a disease called cowpox in cattle, turned out to be, we now know, viruses that are molecularly very similar.

但是导致天花的人痘病毒,和导致牛痘,的牛痘病毒,后来发现其实是,我们现在知道,这两种病毒在分子水平上十分相似

耶鲁公开课 - 生物医学工程探索课程节选