流感疫苗已经用完了。

Doctors have run out of the flu ___vaccine.

最近进行了一项实验来验证疫苗是否有效。

An experiment was recently conducted to verify if the ___vaccine works.

这种新疫苗在临床试验中显示出良好的效果。

The new ___vaccine has shown promising results in clinical trials.