疫苗已经研制出来了。

Vaccines have already been developed.

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美国、英国和中国的科学家已经研制出一种新型隐形眼镜。

A new contact lens has been developed by scientists from America, Britain and China.

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到目前为止，科学家已经研制出了三种药物。

Until now, scientists have made three kinds of drugs.

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Why is it difficult in some cases to produce a vaccine when we've been successful in so many others?

为什么某些疾病的疫苗很难研制,即使我们已经成功生产了很多种疫苗

耶鲁公开课 - 生物医学工程探索课程节选