User blog comment:HaLo2FrEeEk/Full Dawnguard playthrough coming Tuesday!/@comment-4406357-20120626225226/@comment-1080767-20120628043445

Yes, yes you can. Serana has the same blood as Harkon, having been given Vampirism through the power of Coldharbour (Molag Bal), and so if you want, she can feed on you, thereby giving you immediate Vampirism.