There isn't one. There are multiple ways to deal with having the condition, but the only "cure" is to reload.
Biting Enemies - it is possible to take down a certain dragon with just biting.
Vine Spell "Toughen" - 10 HP per cast.
Fiend Spell "Lifesteal"
Statues of Gael Serran - 100% full heal, free.
Later edit for anyone who may search "vampire":
In Skull Castle there is an option to get a "Vampire Ring", which decreases the health draining on your character. You can also delay becoming a vampire until this point. This is the most helpful item in the game for a vampire.
Note that a vampire Dual Wielding or Unarmed (with Keepsake or Breather in offhand) will attack *extremely quickly* at night time. Two enchanted weapons at night on an Assassin vampire is the most damage I have achieved ingame. The Invisibility spell makes it ridiculous. Those who want to keep a Boogre character can counteract their slow speed with this method at night, as well.
Post edited February 04, 2019 by Lysanafae