User blog comment:Merindon1Delicia2/Skyrim Dawnguard Vampire Quests Bugs/@comment-174.70.178.251-20131228192854/@comment-6881629-20151229214910

Go see what's his name (Harkon), if you get cured mid questline he should offer to bite you again, if it doesn't work try seeing if the vampire cure quest works then go back to Harkon and see if he'll bite you.

But if your on the PC and use a custom race mod that hasn't been updated for Dawnguard you will have problems.