Also, the vaccines against polio are not as effective as the smallpoxvaccine, which was so powerful that a single vaccination protected almost everyone.
The vaccinia virus is a non-dangerous virus used in the smallpoxvaccine 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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The reports included a detailed review of the safety of smallpoxvaccine based on historical data as well as recent experience, particularly in the United States.