Zombies are actually quite nice, as long as they ______.
1). In the flesh:
Humans who died in 2009 (with their brain intact) mysteriously rose as zombies. Cities were overrun with the aggressive, man-eating undead. But by 2010, the government had discovered how to "cure" the zombies. By injecting a special chemical into their spine, the zombie's intelligence and memories return.
Most are horrified when they begin to remember what they did while feral. Unfortunately, people with "partially-deceased syndrome" are not really cured by this injection. If they miss a dose, they quickly revert into a dangerous undead cannibal.
2). iZombie:
Zombies are still "mostly" human. But with an incredibly slow metabolism and immunity to most non-cranial injuries. Unfortunately, a zombie must regularly consume a human brain. Or else they devolve into a feral "Romero."
3). The Girl with All The Gifts:
Regular "infected" are feral. But if a pregnant women gets infected, the child develops a partial resistance to the pathogen. They're still contagious and "undead," but remain intelligent. The remaining government raises the zombie children, teaching them to read and write. But if the kids get too hungry, they usually become feral.