Anne, that's what I've always been told too, that once you've had mono, you have a lifetime immunity. And yet my doctor still checks for it every now and again, trying to figure out the elevated WBC and fatigue. So that would seem to imply that it's not an absolute certainty that it doesn't recur.
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When you don't like a thing, change it.
If you can't change it, change the way you think about it.

(Maya Angelou)