You can create work items in Karbon to track sick leave, vacation or even holidays.
We are using Time and Budgets to track PTO. We created a work item using our business as the client and put it on a yearly repeat. When Team members are using PTO, they make a time entry here and it tracks back to their timesheet. It also provides a place where you can see at a glance how much PTO has been used by each person and how much has been used company wide for the year. You can do this for Sick Leave and Holidays. This has been working well for my company.