"In developing countries, that's going to be a longer process where you'll have perhaps business people,farmers, small business people, professionals who will be the first adopters - the doctors,government officials - and then it will slowly as you get more apps (applications) slowly permeate out probably."

VOA: standard.2010.06.25

So, the process of developing a vaccine occurred over a long period of time.

疫苗的发展经历了很长一段时间

耶鲁公开课 - 生物医学工程探索课程节选

So, the process of developing a vaccine occurred over a long period of time.

疫苗的发展经历了很长一段时间

耶鲁公开课 - 生物医学工程探索课程节选