来自《耶鲁大学开放课程：1600年后西方社会的流行病 第14集 第14集》

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  Vaccination is the introduction into the body
  接种疫苗就是将一个致病微生物的
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  of either the whole, or part,
  部分或整体
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  of a disease-causing microorganism,
  引入人体内
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  in order to teach the immune system
  以引起免疫系统
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  to attack that same organism,
  对该微生物的抵抗
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  should it reappear in the body through natural processes.
  以后这种免疫力就会在体内自然再现
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  The mechanism is that the vaccine primes the immune system
  其中原理是疫苗先引起免疫系统
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  to produce antibodies, or teaches immune cells
  制造抗体 或者说让免疫细胞
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  to recognize and attack the organism,
  重组并攻击微生物
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  that we now know perhaps to be a virus,a bacterium,
  微生物可能是病毒 细菌
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  or a parasite of a different kind.
  或者各种寄生虫
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  The problem, of course,
  问题当然在于