It doesn't make sense to me either.
Perhaps the readers of the comics can better explain.
i dont know anything about the comics either, but what i got from the last episode was that everybody is already infected with the virus (or maybe some even are immune to it). it doesnt start to take over unless you die, because i guess the body has the power to f!ght off the virus until you die, then it takes over because our immune system cant f!ght it anymore since you're dead. something along those lines