On February 8th, 2010, an official comic portraying the events prior to Zombie Panic: Source drawn by Henital Gerpes was released. The comic has no dialogue, as that is left up to the reader to imagine. The comic focues on Eugene, Marcus, Jessica, and Paul, with the setting in Town. The comic was created before the introduction of Lea and Vanessa to the game, hence their absence.
It should be noted that Jessica appears in her original attire from the release of the game, as opposed to her current attire.