Now, if we're talking about the kind of Night of the Living Dead zombie virus that automatically infects all of the recently dead, then fair enough, we're fucked (Christ knows how that's supposed to work, mind). But if we're just talking about your 'Infected' brand, a virus that only transmits by bite and only to living humans to create zombies with no instinct except to devour the flesh / brains of the survivors, then yeah, that is not going to spread far. And now I'm going to explain why, using only logic and maths. Gather round.
What we need to establish first is that zombies mindlessly consume flesh. They are incapable of higher thought or strategic thinking; they only want to devour the living. They do not understand that they can increase their numbers by just giving their prey a little nibble on the bum and sending them on their way. When they have a victim, they are going to bite and bite and bite and pull guts and limbs apart until the body of the victim is useless as a zombie. It's just going to be an immobile pile of undead lumps very angrily wobbling on the floor. Zombies reproduce exclusively through the ones that get away: Humans that get attacked, bitten once or twice, and then break free and run off to hide among other humans.
So a human encountering a zombie ends one of three ways: the human gets away clean, the zombie bites them and then they get away, or the zombie bites them, disables them and tears them apart. That means that only one in three zombie encounters results in the infection spreading. That's simplified of course, each result will not be an equal one in three chance, probabilities will shift depending on circumstance and the strength, agility and intelligence of the human. But I'd argue that the probability of spread infection is even less, factoring all that in; a human competent enough to escape is likely to be competent enough to avoid getting bitten, as well.
With all that in mind, zombie hordes are self-defeating because they reproduce far more efficiently when there is LESS of them. One zombie might catch a human by surprise, bite them, and then it would be fairly easy for the human to get away. Then two zombies are on the prowl, probably still easy to get away from, but I'd estimate that once the zombie horde gets to around five or six individuals, the horde is both too large to effectively take anyone by surprise, and also too large for a bitten and wounded human to escape from.
Therefore, shut the fuck up about what you'll do after the zombie apocalypse: Because even if such an infection could exist it's only ever going to be extremely localized. You'd be better off speculating on how you'd survive an apocalypse of carnivorous jam. Have you made a jam plan? Have you looked out of your window and decided on a path you could take that only incorporates inorganic objects that extrude more than three feet from the ground? Buy my book for this and more safety tips.
Yahtzee is a British-born, currently Australian-based writer and gamer with a sweet hat and a chip on his shoulder. When he isn't talking very fast into a headset mic he also designs freeware adventure games. His personal site is www.fullyramblomatic.com.