Well, that sucks. Wonder if it's incomplete immunity... they have the flu, just not a bad case, so they go about their business, infecting everybody, instead of being home in bed like a respectable sick person.
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Here is a link to the Article about the study
https://explainlife.com/cdc-study-v...A8Oe-KVEFpB3wGUca3Xhj-l2p8LI-u_9OdPIntpjzVymk