but it can't act like a

却无法致病的病毒
virus any longer because it can't replicate.

因为这种病毒不能进行复制
Then, they did preliminary

接着研究人员对疫苗在人体中的
studies of safety and effectiveness in people.

安全性和有效性进行初步研究
Basically, injecting it into some test subjects,

他们把疫苗接种到测试对象体内
making sure that they didn't get diseased from it

确定接种者不会感染疾病
and looking at antibody responses to see

同时观察抗体的应答反应
if it worked and it did.

了解疫苗是否有效
So, very rapidly a clinical trial was started.

很快临床试验就可以开始了
Now, the problem, or one of the challenges

现在的问题是
with clinical trials of vaccines

这也是疫苗临床试验的挑战之一
is that you have to enroll a lot of patients into clinical trials

临床试验必须包括足够多的病人