任何特定疫苗的成功都依赖于所谓的免疫屏障，即通过高比率的免疫人群来保护不免疫的个体。

The success of any given vaccine depends on so-called herd immunity, in which a high rate of immunization in a population helps to protect those individuals who are not immune.

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我们的估算表明了2020年之前中国95%将依赖自己的谷物生产，这在国际上算是一个极高的比率。

Our estimation shows that by the year 2020 China will be relying on 95 percent of its own grain production to feed the nation, an extremely high rate in the world.

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但是，如果出口是建立在一个高进口量的基础上的话，这一比率就夸大了一国对于外部需求的依赖性。

But this ratio overstates a country's dependence on external demand if exports have a high import content.

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