Serum 208 is a permanent cure for the afflicted villagers of Mort'ton. It is used during the Shades of Mort'ton quest to turn Afflicted NPCs back into normal characters so the player can interact with them. It is made by using Serum 207 on the sacred flame at the rebuilt temple.
It is suggested it be used on Razmire Keelgan so he will always be coherent for the player and open his general and builder's stores. When used on an afflicted villager, they will turn into Mort'ton locals and reward the player with items. Although it is a "permanent" cure, the villagers always return to their afflicted state, with the exceptions of Razmire and Ulsquire Shauncy when spoken to by the player. Therefore, there is no way to permanently "clean up" Mort'ton.