The Last Man on Earth (1964)
Morgan (Vincent Price) spends three years alone with nothing but plague-infected zombies everywhere, battening himself inside his house at night when they come out, and hunting them down and staking them through the heart by day, while they sleep. He finally runs across Ruth (Franca Bettoia), a woman who has the plague — but what Morgan doesn’t know is that she’s one of a bunch of infected people who’ve discovered a vaccine that staves off the plague’s worst effects (like, turning you into the blood-seeking undead).
But the biggest shock for Morgan is that the plague victims he’s been hunting and killing by day aren’t necessarily the walking dead; he’s unwittingly been killing “normal” (if infected) humans, and for that he’s become a legend in the eyes of the living plague victims — and not in a good way. (Thus the title of Richard Matheson’s novel, I Am Legend.)
Morgan is finally cornered in the church by the living victims, and they kill him… and, we think, they probably end up using his plague-immune blood to completely eradicate the plague from their midst.
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