Between

Viruses that kill off people above a certain age are not a new idea in the realms of science fiction and genre television. You only have to look to long running series such as Stargate Atlantis, Star Trek and Deep Space Nine for examples of individual episodes and then there's full series such as The Tribe and Jeremiah that address the concept. But, with most of these series being at least over ten year's old, it was about time for someone to buff the dust off this trope and give it another try.