In the novel Red Harvest, it revolves around the idea of a zombie virus. Darth Scabrous' experiment creates a plague known as The Sickness, which spreads through bites and contact with fluids and causes the infected to become zombies. These zombies are the gory horror movie type: single-mindedly violent, hungry for flesh, and immune to pain. Unlike most popular zombies, they can't even be killed by removing the head.
The virus resurfaces over 4,000 years later when Darth Vader learns of Scabrous' experiments. The Imperials' attempts to weaponize the zombie virus is simply called "Imperial bioweapons Project I71A." This virus is airborne and causes flu-like symptoms before the infected person dies and becomes a zombie.
During the transportation of said virus, a crack in the faulty container causes the virus to leak out an infect Everyone. Vader fights off the infected as best as he could, but he eventually succumbs to the same virus Scabrous falls to.
My rendition of zombie Vader is made up of parts from 3 different Vaders. The head was drimiled out with a skull added in it. The rest was done with a exacto knife, dry brushing, and a few pieces of wire. Enjoy!