There were no reported cases after that, and so by the late '70s, the world was certified sort of free of smallpox worldwide.

在那之后就再也没有过报告,到七十年代晚些时候,已经确认世界各国都摆脱了天花

耶鲁公开课 - 生物医学工程探索课程节选

None of you got smallpox vaccinations, because once a country was certified to be smallpox free, there was no reason to-- there was no reason to vaccinate people any longer.

你们当中没人接种过天花疫苗,因为一旦一个国家确认不再有天花,就没有理由,就没有理由再给人们接种

耶鲁公开课 - 生物医学工程探索课程节选