How do you cover vacations and days off?

How does your facility hospitals specifically cover days off? I work at a large medical center and the hospital has mostly medical floors and mostly surgical floors. We are discharge planners, case management and utilization reviewers. We work in teams of 2 in medicine, but not in surgery. When someone is off we we have the other 1 person of a 2 person team cover all the new admits, do UR and all discharge planning for the 40 bed unit. A bit overwhelming, leaving the person not off to work extra hours. (salaried of course). In 1 person units, surgery folks, cover surgery folks, and no one covers ob/nursery except other ob/nursery discharge planners.
Sometimes the team managers cover some of the reviews that can be done, but when more than 1 person is out on a team, how is that covered. We work with 3 teams each leading greater than 30 folks. What about unit based social workers, who covers when they are off? I am going to work on a shared governance committee and would like any input.