The 1950s sci-fi pulp author Fredric Brown wrote one of his (then) famous short-short stories about a man who came up with the serum for immortality and took it, but he had a cold at the time, and the germs also developed immortality and reproduced so much that his symptoms got worse and worse and eventually put him into a coma. After a while, his colleagues realized he’d never get out of the coma, so they just buried him.