1. 1981年世界上發(fā)現(xiàn)首例艾滋病例以來(lái)，艾滋病可能已成為當(dāng)今世界面臨的最嚴(yán)重的公共衛(wèi)生問(wèn)題。

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. 從一開(kāi)始研究人員寄希望于靠迅速發(fā)現(xiàn)一種疫苗來(lái)終止艾滋病流行，但迄今為止所試驗(yàn)的多數(shù)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. 為什么一些曾經(jīng)有希望的研究現(xiàn)在半途而廢陷入了死胡同呢？這是因?yàn)榭茖W(xué)家們所對(duì)付的艾滋病是極其困難的科學(xué)挑戰(zhàn)。

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?yàn)楣裘庖呦到y(tǒng)本身，所以在感染有病毒的人身上不會(huì)產(chǎn)生免疫。此外，許多基本問(wèn)題也依然沒(méi)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，沒(méi)人知道什么樣的免疫反應(yīng)能最佳防御艾滋病病毒感染，也沒(méi)有人已經(jīng)搞清楚如何去生產(chǎn)一種疫苗，它在艾滋病病毒在人體內(nèi)站穩(wěn)腳跟之前，就能促使免疫系統(tǒng)產(chǎn)生能夠殺死病毒的抗體。

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. 任何事物都不會(huì)一蹴而就，在醫(yī)學(xué)方面尤其如此。所以研發(fā)出有效的抗艾滋病疫苗還需耐心。

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

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