It was the early to mid 1990s I think. It didn't last past the 2 hour pilot movie. It takes place decades after serum is given to people to extend their lives (and make them young again?). It backfires in most of the population and causes them to deevolve into savages while the others have all the positive benefits and create domed/walled cities to protect them. They only go out when they find uninfected humans that need helped. Pretty vague I know but for some reason i've been thinking of it lately.
