Este é Creche Zumbi por Craig Halloran.
De uma das avaliações da GoodReads:
The book begins with the zombies taking over and one man, Nate, accidently discovering that "Fountain Dew" calms them. Thus, Fountain Dew becomes the zombie tamer and Nate becomes a hero. The book then jumps forward about 10 years when the zombies have all been either captured or killed. There are now "zombie day cares" which house zombie children and scientists experiment on them to find a cure. But not everyone is happy that the remainig zombies were saved. Many people still wish them dead.
E outro:
It starts out during the midst of the zombie take-over with one of the main characters running away from his zombie girlfriend. He can't stand to kill her so by accident he ends up giving her "Fountain Dew" and finds that she stops trying to kill him. With his last battery he tweets the discovery and saves the world. Fast forward a few years and they are trying to find a cure for zombies and controlling them with soft drinks.
Eu encontrei isso quase imediatamente, pesquisando na web por "história de zumbis Nate orvalho da montanha refrigerante".