1. 1981年世界上发现首例艾滋病例以来，艾滋病可能已成为当今世界面临的最严重的公共卫生问题。

Since the first case of AIDS was discovered in 1981 in the world, AIDS has probably become the most serious public health problem facing the world today. 

2. 从一开始研究人员寄希望于靠迅速发现一种疫苗来终止艾滋病流行，但迄今为止所试验的多数疫苗都未能如愿。

From the onset researchers pinned their hopes of ending the AIDS epidemic on the speedy discovery of a vaccine. But most of the vaccines tried so far have failed to live up to expectation. 

3. 为什么一些曾经有希望的研究现在半途而废陷入了死胡同呢？这是因为科学家们所对付的艾滋病是极其困难的科学挑战。

Why are some once-promising researches falling by the wayside and running into dead ends? This is because AIDS that scientists are dealing with is a very formidable scientific challenge.

4.同其他病毒不同，艾滋病病毒因为攻击免疫系统本身，所以在感染有病毒的人身上不会产生免疫。此外，许多基本问题也依然没有答案。

Unlike other viruses, AIDS doesn’t produce immunity in people who are exposed to it because it attacks the immune system itself. In addition, many basic questions also remain unanswered.

5.例如，没人知道什么样的免疫反应能最佳防御艾滋病病毒感染，也没有人已经搞清楚如何去生产一种疫苗，它在艾滋病病毒在人体内站稳脚跟之前，就能促使免疫系统产生能够杀死病毒的抗体。

For instance, no one knows what immune responses best guard against HIV infection. And no one has figured out how to produce a vaccine that can prompt the immune system to generate antibodies capable of killing the AIDS virus，before it establishes a toehold in the body. 

6. 任何事物都不会一蹴而就，在医学方面尤其如此。所以研发出有效的抗艾滋病疫苗还需耐心。

Nothing happens overnight, especially in medicine, and therefore, it will take patience to develop an effective vaccine against AIDS.

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