All That’s Left in the World by Erik Brown 

When Andrew stumbles upon Jamie’s house, he’s injured, starved, and has nothing left to lose. A deadly pathogen has killed off most of the world’s population, including everyone both boys have ever loved. And if this new world has taught them anything, it’s to be scared of what other desperate people will do . . . so why does it seem so easy for them to trust each other?

After danger breaches their shelter, they flee south in search of civilization. But something isn’t… Read more.