I didn't read "The Passage" so I had no idea who was recurring or not. The prolouge helped and I assumed it would all start to make sense. Some characters seemed a bit pointless. Other parts of the story had no explanation-How did they know Layla could manipulate the virals? This book is a vampire-post-apocalyptic but that's not really the point. It uses that setting to tell a character driven story. It kept reminding me of Elizabeth George's mystery stories. Those are not just there for a the mystery aspect. It is used as a way to create great characters. Both write fairly hefty books as well. It's more about the journey than the destination. 
 The dystopian camp of the survivors effectively creates dread and hopelessness. The camp director is vile and you can't wait for him to get his comeuppance. Overall, it was worth the time besides the confusion in places.