Let's assume that zombies are the undead.
The virus doesn't really care about the cell - it usually dies. Sometimes several cells join together, but the effect is negligible. Viruses are interested in their own offspring, but for this they have to kill the cell. Business, nothing personal.
Why is HIV dangerous? It kills the cells responsible for immunity. Along the way, making more copies of itself to kill more cells. Well, life is bad without immunity.
But viruses can indeed change cells. The cells will get larger and grow erratically. The genetic structure of cells is changing to bring more friends to the virus. He alone, poor thing, is bored. The way in which the cell receives energy is changing. Cells also have such an interesting feature: they can stop their growth. Viruses disable this business. And then people get sick chronically, but not in an acute form.
It's very difficult for me to imagine a virus that, after the death of a cell, would like to return its life. They are selfish. A zombie party is boring. Whether it is a matter of mutation - one virus has Kirkorov's head, and the other has Bieber's. Jobs's hand, Lenin's elbow, Lennon's foot. This is a really interesting party.
The boom in films about the death of humanity began in the 1960s, when tension was constantly hanging in the air and the transformation of the world into nuclear dust was quite real. The Cuban missile crisis had a very big impact on art and, in particular, on mass cinema: everyone suddenly realized that the world could perish overnight, and were very impressed by this idea. From that moment on, the genre of apocalyptic narrative began to develop gradually, and zombies joined it in 1968, in George Romero's film "Night of the Living Dead". Although the word "zombie" itself is not mentioned there, the film was revolutionary in the horror genre, and it began the record of the zombie apocalypse fashion. (There were films about zombies, of course, before him; in the 30s and 40s, during the heyday of the horror genre at the Universal studio, but these were all films about terrible isolated cases, and in this perspective - about the epidemic unkillable cannibals - Romero spoke first.)
The secret to the success of zombies in popular culture is probably that these films largely reflect reality - so far metaphorically. The more the media develops as a weapon of mass destruction, the more people generally resemble the living dead, the stronger the herd feeling becomes, the more aggressive any crowd becomes. Hence, a new wave of interest in zombies, already in our millennium. Do I believe in a zombie apocalypse? Of course, it has already happened and is happening before our very eyes, when a large number of people simultaneously, for some unknown reason, lose everything human.
The series "The Walking Dead" and a very popular series of adventure quests based on it became a strong impetus to this half-forgotten theme. Besides, the very successful Last of Us game has increased public attention and interest in the zombie theme.
I don't believe in a zombie apocalypse.
This, like the stories about the uprising of the machines, first appeared in the books of many authors. When they gained popularity, it moved to the big screens.
To answer the second question you need to look at the ZOMBIE wording. Wikipedia gives two definitions: the first is a zombie revived corpse and the second is a person who has lost control of his mind and body. If you look from the point of view of the first, then I do not believe in the zombie apocalypse, if from the point of view of the second, then yes, it is already around us.