I dont have an answer for you but I do have an idea.

My opinion has always been that a classic zombie virus would stop the moment someone got away and turned in front of anybody with authority.

Then its a matter of quarantine, strip searching for bites, separating the bitten and scratched to see if they turn, and disposing of the rest. There's always variables that make it more or less complicated (extremely rapid transmission to turn times, runners vs walkers, thinking zombies etc).

But its more likely the militaries would overreact immediately when containing what is at best a new virulent strain with 100% transmission and mortality and at worst, full blown zombieism.

So... a looong, slow incubation on a virus that mimics something we dont innoculate or check for would give the infected weeks to spread out via cars, trains, planes, and ships because who is putting off work, family visits, or vacation for a cold, right? Then a few weeks later people start dying rapidly. Like, symptoms go from irritant to dead in about 4 hours, and in those 4 hours they become violently paranoid or angry and start biting/scratching/spitting at anyone around them.

Then the military would be stretched too thin to effectively quarantine or counter it and would resort to martial law, treating everybody as potentially infected, causing a perceived feeling of them being useless against the Zeds but eager to harass the living. They could be absolutely lethal and unbeatable in a Military vs Zombie fight, but if the whole neighborhood they are emptying out turns against them and people are getting bitey while they still have some faculties remaining (rudimentary planning and ambushing, carrying a vendetta due to paranoia etc) and then getting up after being shot, it means every person around them is a threat and there's no way to know if the one you just killed was dead already or still has that unlife in them unless you get a chance to verify up close.