Sick days as other wrote is prescribe by a doctor. It doesn't have a limit (e.g. .y college broke his leg and was on sick leave for 1.5 year). And his vacation time accumulated, he didn't use his 26 days first year so the next he had 52 days to use.

Sick leave in my country is not full paid, it is 80%, so people are not that keen on getting it if not needed. On the other hand they are not hit that dramatically if they are sick.