I recently read a fic for another fandom where one of the characters was turned into a vampire, but had trouble with drinking blood because, to him, it tasted disgusting. He later discovers that this is because drinking blood is the equivalent to sex for vampires (literally bloodlust) and this character was asexual when he was human, so, yeah.
And I'd really like to see a take on how Sherlock would deal with this !
((If you would need more ideas for what to do with this, I could link you to the story or give a few more details of some of the things that happened with vampires in the fic or something???))
Bonus points :
-Sherlock and John centric
-^Not in a relationship