First of all: If you haven't seen World War Z yet, stop reading, because major spoilers are about to follow.
The rest of you: It's no secret that World War Z went through tremendous issues behind the scenes including strained budgets and massive reshoots in the final hour. The final product turned out pretty well—you can read our review here—but this apparently wasn't the case originally.
Turns out, the ending that we saw in the film which included Gerry (Brad Pitt) discovering that the zombies don't attack sick people, devising a plan to infect healthy people with a treatable terminal illness to mask them from the zombies, and ultimately being reunited with his family wasn't actually the original ending. What was planned before reshoots and budget issues was a lot larger in scale—but it also really sucked.
Originally planned was having Gerry head to Moscow, and be immediately enlisted in the army. The plot timejumps to a year later, and we see Gerry now rather adept at killing zombies and often having to battle giant hoardes of them—this is part of the reason the ending was cut, it would have been wildly expensive. At some point, Gerry manages to discover that zombies are sensitive to cold weather, and a huge battle sequence follows that involves Gerry and the army attempting to keep as many zombies in the cold as possible, which is pretty easy to do since they're in Russia.
Gerry gets in touch with his wife Karin (Mireille Enos), and explains his discovery to her. This doesn't do her much good since she and their children are staying in a refugee camp in Florida's Everglades National Park. The worst part, though: The camp is, apparently, the type where you have to "have something to trade to survive," and all Karin had to trade was herself. So, basically, she's been prostituting herself out in order to survive. The movie ends with Gerry attempting to get Karin and his kids back, by traveling thousands of miles to the nearest port, then on a boat headed to the coast of Oregon. The end.