The Passage shares many aspects of The Judas Syndrome , for example; main character development prior to its explanation of how the end comes, and its use of multiple characters. The end having come from a plague rather than a nuclear holocaust allowed the planet to better sustain survivors in The Passage, offering an easier "afterlife" than the demoralized planet The Judas Syndrome left its surviving population.
That being said, both surviving communities were forced to push back attacking parties, in The Passage it was the infected humans bent on sucking the blood from their human counterparts, whereas in The Judas Syndrome those that survived were left to fight one another for what remaining resources there was left.
Both books offer up the intense anxiety survivors would experience after an Apocalypse of some design occurred, but the anxiety The Judas Syndrome creates is immediate whereas The Passage jumps ahead 100 years after the virals have already decimated the population. This broke up the anxiety (and the story) for me, and left me feeling like one book had ended while another was starting. Not a bad thing, but an interruption into a world I was just getting comfortable with.
All the same, The Passage was a good read with interesting characters, telling a story of survival and sorrow. If you enjoyed The Passage, then you will enjoy The Judas Syndrome also. If you enjoyed The Passage, then you will enjoy The Judas Syndrome