Isn't it the case for The Walking Dead, that the virus is actually airborne and everybody is already infected and turn when dead, but when they are bitten, they die faster? Its like it's two different things then and then it would make sense for that universe.

Apart from that, another user already mentioned 28 days later which is the most accurate in that sense, but it can be argued if those are really zombies.

In every movie, the dead bodies do also not decompose fully... So one can think of just wait for about 9 months or so until all zombies are decomposed so much that they are no harm anymore... This has also be never shown...