Needfire by Amy Braun
This book can be downloaded and read in iBooks on your Mac or iOS device.
A virus has spread across the country, infecting its victims and turning them into bloodthirsty monsters. Trained soldiers are dispatched to eliminate the threat, no matter how mild the infection seems. Sophia, Isaac, and Reyes live on the run, scavenging what they can and staying away from both sides of the conflict. But all of that changes when one of them becomes infected. As they struggle to find the rumored cure, the three friends begin to realize that the virus isn't what it seems, and that finding it may cost them more than they could ever imagine...