But the body's natural defenses are usually strong enough to prevent an active case.

VOA: special.2009.03.25

So, there's been an active effort to reestablish the process of smallpox vaccination in case that's needed.

为了以防万一,现在正积极重建,能够制造天花疫苗的工艺进程

耶鲁公开课 - 生物医学工程探索课程节选