A buff is someone who has a strong, special interest in something.

VOA: special.2009.05.17

So, if you were someone that was getting it after it had been passed through many people, you wouldn't have as strong or as lengthy a protection as the first individual did.

如果一个疫苗经过很多人的传递,再接种到你身上,你不会获得像第一个接受疫苗的人,那样强效持久的免疫效果

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