许多诊所的季节性流感疫苗已经用完了。

Many clinics have run out of the seasonal flu ___vaccine.

这种新疫苗在临床试验中被证明非常有效。

The new ___vaccine has proven highly effective in clinical trials.

快速开发出一种安全的疫苗对于结束这场大流行至关重要。

The rapid development of a safe ___vaccine was crucial to ending the pandemic.