Our kid was pretty ill Christmas Eve (although not extreme), and stayed the night with us. My wife was more ill than our kid late in December, and was still ill on January 3. Had residual symptoms for at least a week after. I can't be certain, but they might have had COVID-19.
For the past 10 years I never had to take a day off of work for illness. I was in such bad shape the doc told me to take a week off.