Yeah, so for example, you get exposed to-- before there was a vaccine your brother or sister had chickenpox, and so you got exposed to chickenpox naturally through your contact with them.

举个例子来说,如果你生活在这样的环境里,兄弟姐妹们还没接种疫苗就得了水痘,而你通过与他们相接触,在自然情况下接触到了水痘病毒

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