The vaccinia virus is a non-dangerous virus used in the smallpox vaccine because it is related to the variola virus, which is the agent of smallpox.

痘苗病毒使用在牛痘苗时是无害的，因为它与作为传播天花媒介物的天花病毒相关。

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Remember that the lucky thing about the smallpox vaccine was that a naturally occurring attenuated form of the smallpox virus variola called vaccinea was found.

对于天花病毒来说,幸运的是,存在一种自然发生的,被称作痘苗病毒的,天花病毒的衰减疫苗

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