We had this thing about, No, they're not zombies. They're infected. We wanted them to behave in a different way physically, but they also weren't undead. They could die and they will die, but so will you if they catch you.
"Britain is 28 years into this terrible plague of infected people who are violent, rabid humans with a few pockets of uninfected communities. And it centers on a young boy who wants to find a doctor to help his dying mother."