UNAIDS says about 24 percent of the adult population, aged 15 to 49, is infected with the AIDS virus.

VOA: standard.2010.05.10

So, it's awkward to have to wait for a cow to get infected before you can vaccinate a population.

在给人们预防接种之前,你只有干等着,直到有一头奶牛感染了病毒才行

耶鲁公开课 - 生物医学工程探索课程节选

They have predicted that up to one fifth of the Australian population about four million people could be infected by the swine flu virus.

VOA: standard.2009.05.30

An estimated 10 percent of the total population is infected.

VOA: standard.2009.12.02