†Vampire Dust in Elder Scrolls Online is not an alchemical ingredient, but only valuable as loot to be sold for gold.
Vampire Dust is the ash collected from deceased vampires for its alchemical properties. It is dangerous to collect, and is thus highly valued and expensive. Its alchemical effects vary as much as the environments from which the dust is collected. For example, Vampire Dust collected from vampires in Vvardenfell is the only variety known to be able transmit the disease, but because it's the only ingredient capable of it no potion can be made which offers this effect. Dust collected from vampires in Cyrodiil and Skyrim both in turn carry a resistance to diseases and invisibility, both effects carried from their vampiric source.
Void Essence is a type of red gemstone harvested from Flesh Atronach corpses. It should not be confused with the inky substance known as Void Essence, which can be harvested from Shades and other dark spirits associated with the Void but cannot be used for alchemy.
