Edenborn by Nick Sagan

In the wake of the microbial plague that decimated the world, the bioengineered children of Idlewild have spent the last eighteen years raising the next generation to inherit the Earth-a generation both human and post-human, divided into factions by the genetics used to create them. But as the factions clash over the future of humanity, an even deadlier contagion rises from the ashes of the original virus.