I think for a fantasy Pandemic, the Disease is the Disease. Its source is unknown as are the details of its function (letting us have any "disease" card fit the Illness without worrying about particular pathology).
What is the Pandemic: It's a disease. It's lethal to normals, can't be trivially handled by magic (much like Powerstone
Phthisis), and is capable of transmitting itself within and across communities, suggesting it has many kinds of Carrier (See also
Carrier type. I would like us to have Carriers.) More importantly, what does the Pandemic do? I think the answer is "everything". It needs to cause people to waste away and die and it needs to create more visceral gribbly monsters. Side note:
Stand Still, Stay SilentWhat is it made of: Magic and/or Microbes. Probably And. Not counting any macroscopic forms, of course.
Where did it come from: This should be a mystery.
White: Cure and Quarantine
Blue: Research and Understand
Black: Spread and Profiteer
Red: Loner Survivalism and Opportunistic Anarchism
Green: General Survival and Survival of the Fittest
To me, this is


VERSUS



. White and Blue both want to preserve order, but have different ways of doing it. White is authoritarian and direct, blue is academic and indirect. Ultimately, blue forces rely on white forces to buy time and white on blue to provide a wincon. Black, Red, and Green are all essentially "Pro Illness". Black will use it as a weapon, infecting enemies and turning a profit on misery. Red won't help, they'll self isolate and back it up with ranged weapons for anyone who comes close -- the classic "Lone Wolf" survivor with a bunker full of guns is Red. On the other side, Red forces that can't go solo won't actively promote disease like black, but WILL still abuse the disruption it causes for their own ends. The order of the world is strained, they'll try to break it. Green is only concerned with living. Natural immunity, natural recovery, or accepting the illness and becoming horrible mutants. Naturally. Green is the Papa Nurgle faction here, especially since they'd reject the authoritarian side of white and the "wisdom" of blue.

is the most plague-friendly color, assuming it's not maliciously created by dark forces (implying black). They like what's "natural" and also like community, which promotes spread. Green is Anti-Vax.

is the most plague-unfriendly color, it wants this aberration exterminated. These are two colors that are normally allies but they're huge enemies here.