I think that in the next episodes Jack is going to be “infected” or “claimed” and here is my theory.
in the episode 3 “what Kate does” Dogen tested Sayid passing electricity to his body with wired needles and burning him with a hot iron bar living him a scar in his belly. Dogen did this to test if Sayid is claimed by the evil spirit. the last episode lighthouse Claire show’s Jin a scar in her shoulder and she tell him that she also being tested the same way Sayid does with needles etc.. Ok let’s see jack now. In the first episode of season 6 ‘’LAX’’ Jack is in the airplane lavatory, jack feels a pain in his neck and he finds out that there is a small scar. If you look closely this scar is exactly under a vain so it seems to me that this is a scar from a needle. In the last episode ‘’lighthouse’’ jack find's out another scar this time in the left side of his belly It seems obvious that jack has the same scars with sayid, one from a needle and the other from the burn with the iron bar in his belly Clair have that scar on his shoulder and she also confi! rm about the needles. When jack meet Dogen after his conversation with Sayid Dogen explains to jack that if sayid stay’s alive the infection is going to be spread so I think in the next episodes Sayid infects jack and Dogen did the same test to jack. I don’t have a clue why jack carrying out the scars in the flash sideways and I hope someone post something in the comments.
Thank you all for reading my theory and feel free to comment and im sorry about my English Im Greek.