What do we know about the plague in The Omega Man?

Question

Either from the movie or novelization?

My impression just from repeated watching is that the plague is often fatal but if one survives, it is disfiguring. It is implied that it might affect cognition but are the people in the cult any crazier than the Manson Family (which I think was clearly the inspiration for the group in the movie)? Moreover, I believe that the cult worked with unaffected people at some point to try to rebuild society -- so the crazy beliefs may not be due to the effects of the plague at all -- they become antitechnology because the leader decided this was their core belief?

The single "vampiric" aspect is that the affected avoid the sun because, similar to the Will Smith flick but not as extreme, they lack pigmentation. In the Smith version, they seem to implausibly combust but that does not happen in Omega Man.

Answer 1

The following description was edited from I Am Legend Wiki/Fandom, and describes the creatures from the original novel:

Vampires are the antagonists of Richard Matheson's 1954 novel "I Am Legend". They are humans, both living and undead, who were infected with a bacteria that Neville, the protagonist, called Vampiris. There are two kinds of vampires. The first, the "true" vampires, are corpses reanimated by Vampiris. They are mostly mindless creatures, searching for blood to drink and even resorting to cannibalism when other prey is scarce. These vampires are not very strong or intelligent. The second kind are the living hosts of Vampiris. While they exhibit all the physical symptoms of vampirism, they, unlike the undead vampires, retain most of their higher levels of intelligence and humanity, enough to rebuild society. Those infected with Vampiris will suffer vampirism-like symptoms; they will go hysterically blind near mirrors, they cannot stand sunlight or garlic, their canines will grow into fangs, and they will develop a bulletproof adhesive and a craving for blood. Vampires with a Christian background will also take the cross as a sign of betrayal and be repelled by it. Also, due to the bacteria's anaerobic nature inside the body, if a vampire is cut deeply enough, the Vampiris bacteria in their body will sporulate into dust and escape, reducing the former host to powder and killing them.

Regarding "The Omega Man", I Am legend's third film version (counting Night of the Living Dead), the mutants seem not to be undead, just averse to bright light. The following description is also from I Am Legend Wiki/Fandom.

The Family are an insane group of mutated humans led by Jonathan Matthias. They reject sophisticated technology, as they believe it was the cause of the end of the civilized world. Their skin, hair and eyes lack pigmentation and they are also sensitive to light. Because of this, they are nocturnal and wear simple robes and aviator sunglasses.