Actually, it was 2 seperate series. One was turned into the show and the other was turned into the game. So therefore person above you are wrong in a few ways.
It was originally a comic in 2 different formats which followed the same general storyline. One in graphic novel size, one in classic comic length.
The show is the series developing into another medium. It still follows the same general plot line also, with the director adding his own creativity to the mix.
The game, is a prologue to the general plot line that is The Walking Dead. They are all Walking Dead, one series, four mediums.
Anyway, do you have any idea when the next one comes?