US Academia and sick days
For full-time faculty, the question doesn't really apply well because faculty aren't paid hourly or daily.  In the departments I've been involved with, the policy is that faculty handle their own classes and minor illnesses.  That is, if I need to cancel class one day then what that means for the class is up to me.  Maybe I have a TA teach it, or I offer a recorded lecture to fill in time, or even just cancel the class and adjust material accordingly.

What it comes down to is whether I can meet the obligations for the class while handling my illness.  For major illnesses where that isn't true, the department would schedule someone else to teach and I would look at my short-term disability benefits, which are commonly available in large US universities.  The unfortunate exception is an adjunct faculty member, who simply teaches contract-to-contract, and may not even have benefits through the university.