The Plague of the Sixth Pass is one of the most famous epidemics of Pernese history, thanks to the Ballad of Moreta's Ride. It was believed to be a form of influenza. The Masterhealer of the time rediscovered the secret of vaccination, and, with the help of the Dragons and their ability to time it, immunized the population against the possibility of a second outbreak. This Plague is described in the novels Moreta: Dragonrider of Pern and Nerilka's Story and the Beyond Between