Board Thread:Skyrim/@comment-11204276-20130822224324/@comment-4564061-20150504041402

You can contract Vampirism by being attacked by a Vampire.

Excerpt:

''Sanguinare Vampiris is the disease that eventually culminates in vampirism and is typically contracted when attacked by a vampire, either with physical attacks or being subject to their Vampiric Drain spell. If one is attacked by Vampiric Drain, there is 10% chance of infection.''