【英语时差8,16】疫苗的神奇作用（下）

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The second type of vaccine¹ contains an attenuated² virus. This virus is alive, but has been grown in the lab for several generations, so it isn’t able to multiply very well in humans. With the attenuated virus multiplying very slowly, your body is able to produce the correct antibodies before you get sick. Measles³ and mumps⁴ vaccines⁵ are both made with attenuated viruses. When most people in a community have become resistant⁶ to the virus, either through a vaccination⁷ or by having the virus and recovering, the community develops what is called “herd⁸ immunity⁹”. The nice thing about herd immunity is that it becomes statistically¹⁰ less likely for the germ to find a person without immunity. This protects members of the community who haven’t been vaccinated¹¹, or had the disease, by reducing their chances of encountering an infected person.

 

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