President Obama got the most applause from opposition Republicans when he said the number-one focus in the coming year would be on creating jobs and giving a boost to small businesses.

VOA: standard.2010.01.28

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