"Kira didn't speed up, watching Jayden's face as she walked casually to the wagon. He looked so much like Madison." That's such an awkward sentence, I don't even know where to begin. There is absolutely no rhythm, and what's with the sudden reminder that he's Madison's brother? We know! You told us in the last chapter!
If Jayden and Madison are the only living relatives in the world, and hailed as proof that immunity is inherited, what are they doing wandering around in suburbia? Why aren't they being probed like lab rats by the authorities? It seems these supposedly dedicated scientists are ignoring a lead dangling right under their noses. Fail #1, my dear Kira.