二十多年来，科学家们一直努力研制预防艾滋病毒感染的疫苗。最近的一次失败发生于去年九月份。研究人员中止了药品公司默克的两项实验艾滋疫苗研究。……
The report says prevention programs can be effective if governments invest at least thirty cents a year per person.For more than twenty years, scientists have been trying to develop a vaccine to prevent H.I.V. infection. The latest failures came last September. Researchers halted two s…