There were also failed vaccinations that led to complications,

也有不成功而引起并发症的接种案例
and Jenner made a crucial mistake.

而且詹纳犯了一个严重的错误
He made it an article of dogmatic faith that the immunity

他像信奉教条那样相信人工天花接种
derived from smallpox vaccination artificially was

带来的抵抗力已经是终身保留的了
life-long, just like the natural immunity

就像自然生病活得的天花免疫力那样
that was acquired, and he steadfastly refused to

他坚定地否认与他的信条
consider evidence that ran counter to his dogma.

相悖的证据
In fact,

事实是
artificial immunity wears off,

人工免疫力会逐渐减弱
it's now known, after a period that's not quite

我们现在知道经过一段不太确定
understood, but ten, fifteen,

多久的时间大概十十五二十年
twenty years, and requires,

被接种人就需要