I've been wondering how there are THAT many zombies around in the first place. When humans die in this universe, they're generally either killed outright or straight-up devoured - either way there isn't anything that can reanimate. Likewise, when you die, it can take minutes to many hours to reanimate, during which time your corpse is a ready-made buffet for the walkers. Where are the undead coming from?
In a fiction like this, you have to work backwards through it. One has to sort of assume that the initial event was the fever going pandemic as a result of seemingly spontaneous postmortem reanimation. That's the only way to account for whole metropolitan populaces of reanimated dead. The first resurrection(s) were likely an event related to the thing they all carry. Around 150,000 people die of natural causes each day on earth. That could be over a million people worldwide in a week that would reanimate without having been bitten & might not necessarily be in danger of being eaten
Plus, we don't really know the history of the initial event. Was it a situation where people began dying & reanimated? or was it a situation where the dead rose up? or both? Morgues & funeral parlors overflowing with recently dead, plus more dying naturally daily, & the escalation of the dead infecting the living & causing more death
Basically there could have been a mass population of reanimated dead before the feeding frenzy that depleted most of the remaining population really got going. Most times the only people who get consumed are attacked by larger numbers. The early victims wouldn't necessarily be attacked by a pack. They'd have been bitten by a single individual in their locality, gotten the fever, & died. In short order there was many walkers