Remember, they've all acknowledged it's a bigass island and that no one goes to the black territories (or whatever it was called where that ship was). I mean think of all the stuff that they've found running around the island: the plane, the ship with dynamite, the caves. They've never run into the 'others' and where they stay unless the others want something to do with them. Plus the chick in the hole said 'flight 815' so either she's be slipped to the same alternate time as sawyer 😍 and mike AND jin(which seems unlikely as jin and the other two were separated as was the girl, so we're talking three space-time continums that ALL wind up at the same time? No, it's a new part of the island, maybe the dark territories and the natives are immune to whatever it is and whatever desmond injects may be serum from the natives who are immune.
I'm more disturbed by the polar bear that mike gave walt as a child. There is something with the polar bear he gave him, the one they shot, and the one in hurley's comic book. Also, they candy bars kate was eating were called 'apollo' which may be another clue as to what was going on. She also moved the unmarked crates to climb on and i think those might contain something good.
