Severe illness jump (General)
And then, because it's a movie, a hero would emerge .. who finds an unlikely cure in the form of an amino acid found in something very common, like geckos or seaweed.
Haha - i do remember you saying a long time ago the cure could be slug slime, but it would never see the light of day because it can't be patented.
But if most people are already dead then they'd probably be less worried about cures having to primarily benefit big drug company executives (who'd be dead anyway.