When I have questions, I turn to the gospel of Romero.
It says any amount will kill you in time, depending on proximity to the heart and on vitality/health of victim. 2 days seems to be the longest according to the prophet, but as in walking dead everyone that dies will turn.
Even Romero did not stay completely true to form. He directed 5 or 6 "Zombie" type films. The way the disease is passes if different in some.
I am speaking totally out of turn. My wife is the authority on this.