文章最後一句說，過去因為廣泛接種天花疫苗，人們有免疫力。而今天花疫苗罕用，所以現代人缺乏免疫力，導致病毒傳播快。

來源: ialord 於 2022-05-22 21:21:51 [博客] [舊帖] [給我悄悄話] 本文已被閱讀：次

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