It's not active in a new game until you have a played Sim start it. I'm on the 3rd, going into the 4th, generation in my current game and have yet to do it. The Cahills living at the crashed plane in my game are, literally, George's grandson and his wife and children.
The only hint I've seen that something is going on that needs investigating is once I saw an infected sim walking down the street in the Shady Acres neighborhood. It doesn't spread at all if the player has not done anything to start the progression of the story.
You don't need to "deactivate" the pack, just don't have a sim start the story for it, and you will be fine.
