As I am sure everyone here is aware one can become a vampire without the DLC. Now, I got curious as to what happens if you start off this DLC as a vampire. What happens? I mean, clearly you cannot meet the Dawnguard that will send you on your merry way towards Serana as they will hunt you down, right? Well, then how do you meet her, and how does Harkon react if you meet him as a vampire to begin with? Is there a special introduction in that case?

no its all the same dawnguard send you on your way and harkon says you only caught a disease

When you meet Serana as a vampire, she asks if youw with her father. You tell her you are with the Dawnguard and she proceeds to say "Well, that is not a name a group of vampires would choose."

The player then asks: "How did you know I was a vampire?"

She replies: "What? You don't think I can tell my own kind? I smelled you before I opened my eyes."

Harkon simply offers you the gift, the player then asks "I am already a vampire. What else can you possibly offer me?"

He then says it is a baser form of vampirism or something, just a disease while his blood is true power.

Its all the same other then a couple lines of dialog.

Not true. It is tweaked.

When first meeting with the Dawnguard, there is no major difference. There is some differences in the Awakening and Bloodline quests, pretty much coming down to comments about already being a vampire, and Serenia saying she knew, as she can detect her own kind.

Oh and if you mention to Harkon that your already a vampire, he makes a disparaging comment about having a mere disease, and offering 'true' vampirism. You get similar commentary if your a werewolf.

Oh, cool. I've thought of making my character a vampire before the DLC hits PC, see. Just need to make sure it wouldn't screw anything up. Then next step will be making sure not every vampire you meet out in the world stays hostile to you when you're in Vampire Lord form. After all, you're a supervampire, they would not want to feed off you. :3