This is an addendum post to "How to Write A Zombie Novel" based on an observant reader's comment about the controversy over Zombies versus Infected. The difference may not be immediately obvious to the layman but is actually rather controversial in some circles.
The difference is, in simple terms, Zombies (capital Z) are dead people who have risen from the grave while Infected are individuals who are sick yet now gruesomely savage. The latter was popularized by the games Left 4 Dead and 28 Days Later, both depicting a "different" kind of (lower case z) zombie which was both fast-moving as well as more intelligent than the Romero undead. Amusingly, the Return of the Living Dead movies predate both with their own version of an "intelligent" zombie. One might argue, indeed, they represent the initial split between the concept of zombies and Infected.
There's considerable overlap between these zombies and Infected. Indeed, I actually just use the term zombie whenever I refer to them in my hash-tags. However, the differences between the two types of zombie can mean a major difference between how the monster is handled in the story. As mentioned, the Zombie is very much based on George Romero's model. They are dead rather than sick and are not required to follow much in the way of biological rules.
Zombies can be shot, chopped up, and set on fire without causing them overdue distress. They also tend to be slow-moving because, obviously enough, they are rotting. There's a definite building-dread to these creatures that, ironically, is similar to how human beings became the dominant species on Earth.
Everyone knows cheetahs are faster than human beings. So are a lot of animals. However, something I learned in college was human beings are actually much better at endurance walks. So, when they caught up to their prey, they were fresh and the latter were dead tired. Zombies are much like this. Our hero can spend the entire movie running away from them but they, unlike their pursuers, have to catch their breath and sleep. The Zombie is like death. You can escape it every day of your life but it will catch you.
In this respect, the mindlessness of the Zombie is also part of its appeal. A Zombie is a very impersonal sort of killer. George Romero's movies even sympathize with the creatures to a certain extent, highlighting they're remnants of humanity rather than just purely evil. A Zombie's bite will kill you and turn you into a monster but it bears no malice or anger. Thus, a Zombie serves as a decent enough stand-in for death.
Infected, by contrast, are a bit more hard science. While rising from the dead as a shambling horror is still, for now, in the realm of fantasy--we have people attacking people in savage ways all the time. Rabies, drug-cocktails, violent schizophrenia, and other conditions make it plausible (if unlikely) that something akin to a zombie attack could occur.
In short, Infected are "living" zombies. This doesn't mean that Infected can be cured. Far from it. The majority of depictions have them as brain-dead but possessing only aggressive instincts and hunger. In short, they're living people have been reduced to a state of heightened mania. This, theoretically, means they're vulnerable to damage (even if they don't feel pain) and have a need to eat as well as sleep.
Infected, due to the fact they're still alive, are not rotting creatures. They are able to run, attack, and reason to a certain degree. They are as intelligent as animals, for the most part, and may display some communal behaviors. Amusingly, this would apply to the first George Romero zombie who ran after Judith O'Dea's character in a cemetery before trying to break into her car with a rock.
Resident Evil shows some of the benefits of Infected in they can be adjusted to fit non-zombie motifs. Infected can be linked to mutants and turn into all manner of horrible and disgusting monsters. While Zombies can theoretically be turned into horrible abominations, in general, they tend to be associated with rotting and have no real bodily processes.
The differences between Zombies and Infected have long-term consequences for each other. Zombies can stay animated forever or will, eventually, rot to pieces. They are supernatural beings and can follow any rules you want to establish for them. They have no natural life-cycle and thus can do more or less anything you want them to. The Infected, on the other hand, should have whatever sort of life-cycle (for lack of a better term) described.
In most cases, the Infected don't have to last forever. The initial outbreak is terrifying enough as it is. However, unless you intend to have them die of "natural causes" you might want to think of a crude life cycle of the creatures as time wears on. Do they continue to wear the clothes they wore until they're tattered stinking remnants or do they put on clothing out of habit? Do they sleep, hibernate, or enter a kind of weird stasis? Do they hate the light and love the dark or prowl around during the day? These can add a lot of fun to your book if thought about to their natural conclusions as well as interject a kind of fun realism.
There's no reason the two kinds of undead can't overlap, though. Zombies can run, the Infected can display almost supernatural qualities, and the two sides may blend however the author may desire. In one Call of Cthulhu scenario, protoplasmic aliens take residence in corpses and then re-animate it despite "life" no longer following the functions of a normal human. The intelligent aliens of Dark City are animating the corpses of humans for similar reasons. Likewise, the use of Zombies as metaphors for disease predates the creation of Infected.
There's no reason authors must keep a strict divide between the two in their books but if they want to, bearing in mind these qualities might benefit them. Thanks for reading, folks!
* Special thanks to Neil Cohen and Rob Pegler.