The biggest evidence against it would be that the plague ridden populace (known as The Infected) are NOT actually zombies. So let's try to define what a zombie is. A zombie is any human reanimated from death and devolved to a primitive state where there primary, if not only, motive is to consume. They lack emotion, personality, and pretty much any other characteristic of the deceased except echoes of memories of their former life that lead them to repeat normal actions albeit purposelessly. They also suffer from rigor mortis, stiffening of the body that happens after death. Thus the slow, shuffle in which pre-Zack Snyder zombies moved.
The Infected are otherwise very different. They are not emotionless. They are full of rage, like an amped up form of rabies. Since they are sick and not dead, they are not held back by rigor mortis. In fact, quite the opposite, they become fairly fast moving and never seem to get exhausted. They definitely have the same penchant to attack, but their is no clear cut implication that they are motivated by hunger.
You would think that the most important element to be considered a zombie movie is to have to include zombies, which the Infected certainly are not, but 28 Days Later... still has most of the same characteristics that have brought so many fans to the sub genre in the first place. In 28 Days Later, the events that ruined London already occurred and out hero, Jim, awakes in a hospital and wanders the streets of an empty, but severely damaged London. It is a frightening image, an empty city. The realization that everyone is gone, even in the early mornings can be pretty creepy. That is one of the biggest sources of fear between both kinda of flick, the fear that no one is there, that you are alone. And not just by yourself, ultimately alone, never to have human companionship again. Zombie movies are really the only ones to effectively depict such a fear. 28 Weeks Later is about the grand reopening of London, that is until they are overwhelmed by the last of the Infected. An uncontrollable enemy hiding behind the faces of neighbors and loved ones is yet another fear device that is used most effectively in zombie movies. How many heroes or victims have hesitated thinking they can talk their zombified friends into consciousness? Too many. In fact, I believe this to be the real defining characteristic of zombie movies. That the enemy is a disease, an enemy you cannot shoot or stab, until it has infected your loved ones and turn them against you.
You might want to say that vampires and werewolves are similar. And they sort of are. But the biggest difference is those two monsters are almost always portrayed with so much more human capabilities than the zombies or infected. The victims' personalities tend to fight the diseases' hard-wiring. Basically, my point is 28 Days Later.... and its sequel have a fundamental difference from the zombie sub genre, but they have so much more in common, is it really necessary to mention how it doesn't count every time it is brought up in a conversation of zombies? Not at all. It has more in common with the zombie movies than the Dawn of the Dead remake or Zombieland which pretty much ignored many of the important aspects of a zombie yet labeled them as such anyway. At least 28 whatever later was honest about what it was accomplishing.
