One that was developed a number of years ago but has been perfected and refined in recent years with very, very good research.

该概念很多年前就已经提出了,但在近年通过高水平的研究才被改进完善

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

Some, like the smallpox vaccine on one exposure generates a very high response that lasts for many years so you don't need a boost.

有一些疫苗,比如接触一次天花疫苗后,人体就能产生高水平的免疫应答,并持续很多年,所以无需再次接种

耶鲁公开课 - 生物医学工程探索课程节选