that's kind of a myopic view.
Do you believe in rabid raccoons?
IE.. an animal that acts agressive and out of the ordinary due to a viral infection?
Some of the best 'zombie' movies I've ever watched were about 'zombies' that were nothing mor ethan 'infected' humans. the infection ranged from a variaety of different diseases.. most fictional.. some.. a real stretch of reality.. some.. sorta possible ina bad set of circumstances.
zombie genre covers a wide variety of origins
Youv'e got the supernatural zombie.. IE.. literally re-animated dead ( perhaps under the control of some other supernatural or evil religious person .. demon, vampire.. etc.
you've got the reanimated dead, that are suposedly animate due to some sort of parasite or other micro-organism, disease.. etc.. but are really dead.. no heartbeat.. they rot like a corps.. but apepar to exhibit human traits like hunger.. and seem to still have senses.. even if the eyes are ruined..e tc.. and have smell even with no lung movement. 'the walking dead' seems to have these. they are DEAD .. but animate.. and not otherwise evil or supernatural.
Youve got the voodoo zombie, ie.. a living person under some deep level mind control ( though I have seen stories of voodoo zombies being like the first type I mentioned.. etc.. )
then you have the crazy person zombie... the ones I liek the most. IE.. living person.. heart beat.. etc.. but they are insane / enraged and or out of their mind.. animalistic.. as they get injured or starve.. they get slow.. they don't use tactics.. they are the stereotypical 'rabid raccoon'. movies like 28 days / weeks depict this type, as well as all the B movies where some scientist drops a vial of expiremental yeast.. and then there is a military lockdown as all the scientists are now maneaters and crazy.
that last one is the one I like the most. It's at least plausible. I like science fiction as much a sthe next person.. but I like it even more if there is plausibility involved. In the case of supernatural / evil... that would be my 2nd choice... unverifiable plausibility I guess..
the third type seems so implausible to mee that I rank it as 3. I mean.. if these were the zombies attacking. wait a few weeks and they will simply rot or be predated by insects. or if in hot weather.. dessicate.. or int he cold.. freeze. a zombie apocalypse of the '3rd ' type would last, AT MOST , a couple months.. as long as the surviving humans just sat tight and prevented themselves from becoming vectors. The worst of it may be a week or 2 at the MOST!.. then after that you might have a bunch of immobile zombie- parts laying around. dead tissue just tends to fall a apart in the elements.....
I don't care for the voodoo stuff at all.. so it's least favorite.