As far as I can tell, this informant came to him.

据目前所知 是线人主动找到的他

provided you authorize it.

我们就能知道更多

The adult population therefore possessed what we might call

因此 成年人群拥有了我们所谓的

So, it became an endemic disease of childhood.

因而 天花演变为童年时期的地方病

So, you couldn't introduce the live virus in

所以 不可以直接接种活体病毒

Remember that the lucky thing about the smallpox vaccine was that

对于天花病毒来说 幸运的是

The problem, of course,

问题当然在于

Jenner benefited from the cross-over immunity

詹纳利用了牛痘与天花的

is that the vaccine stimulates these particular cells

疫苗通过刺激免疫系统中的

We're usually talking about adaptive immunity here.

这就是我们经常说的获得性免疫