In the latest developer diary for Prototype 2 the development team explains the how the upcoming open-world game is broken into zones that have unique characteristics. With the viral outbreak of the Prototype storyline, each zone will feature different areas where the virus comes into play. Unlocked in linear fashion, you’ll encounter a militarized zone, an infected zone, and a normal zone. As these areas are unlocked, you’ll get the chance to travel back and forth doing what you want, as is the calling card of the franchise.
There’s no concrete release date on Prototype 2, but best guesses estimate that the sequel will be heading out in the second quarter of 2012.