Supernatural vs rabies
Quarantine started out as some virus that made ppl go crazy, sort of like 28 days later, but then obviously at the end we see this ugly creature however we don't know if it's a person who evolved into a deformed person from the virus, or an actual monster. In REC3, it became about supernatural forces that turned ppl into these "zombies" and responded to bible versus (from what I recall)
I personally would prefer if they stuck to it being a rabies virus. More scary and plausible.