When I retired I had months of sick leave on the books, and I took off every time I got sick...I was only paid for a tiny fraction of the sick hours when I left. But you are right, some of the folks where I worked had the flu every Monday and many times on Friday as well. Then when they really got sick, they were in a pickle, so they would come to work sick, trying to act like a hero, coughing and sneezing all over everything, spreading their joy with everyone else.
When I was working, I would get a flu-like illness about every three or four months. Since I have retired seven years ago, I have not had a snifffle. Working is bad for your health.