Vampirism
Vampirism is the belief in the existence of vampires such that it may manifest the characteristics of vampires in people.
Vampirism makes a return to Skyrim. As was the case in the previous game, Oblivion, the player has a chance of contracting a disease called Sanguinare Vampiris. The initial disease can be cured normally, but if left unchecked for three nights, the diseased will become a vampire.
Full vampirism is difficult to cure and made up of four distinct stages. The disease progresses every 24 hours a vampire goes without feeding on a sleeping NPC. Feeding always returns you to stage one.
These are the four stages to vampirism. The effects of the debuffs are amplified with each stage advancement.
Stage 1
Increased Resist Frost by 25%
Attributes reduced by 15 points in the sunlight.
Weakness to Fire 25%
Gain abilities Vampire's Sight, Vampiric Drain, Vampire's Servant
Stage 2
Increased Resist Frost by 50%
Attributes reduced by 30 points in the sunlight.
Weakness to Fire 50%
Gain ability Vampire's Seduction
Stage 3
Increased Resist Frost by 75%
Attributes reduced by 45 points in the sunlight.
Weakness to Fire 75%
Stronger versions of existing abilities
Disadvtange: Most NPC's will not interact with you
Stage 4
Increased Resist Frost by 100%
Attributes reduced by 60 points in the sunlight.
Weakness to Fire 100%
Gain abilities Embrace of Shadows and upgraded Vampiric Drain and Vampire's Servant.
Disadvantage: You will be attacked by the citizens of Skyrim for being a vampire.
Stealth-type characters profit the most from the bonuses of vampirism, but the disadvantages are rather inconvenient for other character archetypes.
Advantages
Immunity to diseases
Immunity to poison
Increased frost resistance
Illusion spells are 25% more powerful
Harder to detect by 25% when sneaking
Attributes do not regenerate in the sunlight
How to Contract Vampirism
You'll need to come in contact with another vampire. Each hit by a vampiric enemy has a chance of passing the Sanguinare Vampiris disease onto you.
You can find vampires in Haemar's Shame, a cave to the southwest of Ivarstead. If you want to contract Vampirism, go there and let the vampires attack you.
The effects of the disease do not take hold immediately, as the transformation is gradual if left unattended. In the previous game, it took three in-game days to consummate the conversion to vampirism, after which the player assumes all the perks and downsides of being a vampire.
How to Feed as a Vampire
Once afflicted with Vampirism, you will slowly progress through the four stages, eventually becoming "blood-starved." At this stage in the disease, most people will not talk with you and will instead attack you.
In order to regress to earlier stages of vampirism, you will need to feed. You can feed only on sleeping humans, which you can find in most towns. Sneak into their homes, creep up behind them while they sleep and, while crouching, the option to "Pickpocket" should appear. Choose to pickpocket and you will further be given the option to "Pickpocket" or "Feed." Choose to feed and the deed will be done without disturbing the sleeping target.
How to Cure Vampirism
If you rid the disease early on before the onset of symptoms, then a simple Cure Disease will do the trick or going to temples in towns and using the altar. At later stages, however, it is still possible to cure yourself by resorting to Lycanthropy or doing the quest Rising at Dawn. However, becoming a lycanthrope is permanent unless you progress through the companions and it has its own costs and benefits.
