In fact, in 2009, they nearly got there, when a large trial in Thailand showed an experimental vaccine protected about one third of the people who received it from HIV infection.

实际上，2009年，科学家们几乎已经成功了，当时泰国的一个大实验证明了一种实验疫苗保护了三分之一感染HIV病毒的人群。

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Early results showed that, rather than preventing HIV or reducing the viral load in people who received it, the experimental vaccine may have increased their chances of become infected.

早期的研究结果表明，实验用疫苗有可能增加人们感染HIV的几率，而不是预防感染或者降低感染者的病毒载量。

youdao

Portuguese scientists said they had developed an experimental vaccine against tooth decay which was successful in laboratory tests on rats and could pave the way for a version that works for humans.

葡萄牙科学家说，他们研发出一种实验性疫苗能防止蛀牙，而它已在实验室的老鼠身上证实有效，这将有助开发防止人类龋齿的疫苗。

youdao

Scientists say an experimental vaccine reduced the risk of infection in human beings by thirty-one percent and was safe.

VOA: special.2009.10.13

Scientists say an experimental vaccine reduced the risk of infection in humans by thirty-one percent and was safe.

VOA: special.2009.09.30

Researchers first developed an experimental vaccine against East Coast fever thirty years ago.

VOA: special.2009.11.03

There, Escherichia coli bacteria are growing to produce an experimental vaccine against influenza.

FORBES: Government Backs Futuristic Flu Shots

The experimental vaccine protected only one of the six volunteers in the trial.

FORBES: Booster Shot

If you give a group of people an experimental vaccine and none of them gets ill, have you protected them, or just been lucky?

ECONOMIST: An ounce of prevention . . . | The