Zombies?
Nah...
World War III would be more effective.
--
Taking out the fact that science is a big troll, we have to consider that a zombie apocalypse would
not be noticed in the first weeks, due to obvious reasons.
So imagine if you were at home, watching television in your couch, then all of sudden zombies, lots of them, punching your door desperately trying to eat your flesh...result = You're dead.
Now let's do it again, you're walking in the street, alone, around midnight, and there's a horde(not necessarily, just 8 or 10) zombies roaming you, you don't know that they are zombies, because probably they're not yet in state of decay, smelling? Yeah, probably a beggar, you think. You have no idea of what is going on, and you try to avoid them(C'mon, it's midnight), suddenly you get surrounded. You can miraculously escape without a bite and go home(see above) or run to a police station(wich wouldn't be a good idea either. Quick explanation = ammo and noise)
Oh, and by the way, we wouldn't even know what type of disease it would be, so it could be very contagious or not contagious at all.
Tl;dr : We would be caught offguard.