The good news is that Azerothian zombies, just like in most movies, move slow. Just be sure to stay farther than 21 yards away from them as they have Retch! a ranged spell that will slow anyone within the area of effect. This is the smoky green cloud on the ground you see in all those screenshots. They can also summon a burst of speed using Lurch! so don't be too confident that they won't close the distance. That ability also frees them from movement impairing effects so trapping them or slowing them isn't a guarantee you'll be able to stay away from them. The idea is to kite the zombies, because getting into melee range with them is a very bad idea.