I was waitlisted at Vanderbilt last year and it was certainly one of my top choices and I really wanted to go there, but couldn't commit to telling them that I would go there if I was taken off of the waitlist.
Anyhow, if you are really set on getting into Vanderbilt, it will be in your best interests to continually update them and to tell them that "I will attend Vanderbilt if taken off of the waitlist." Bear in mind this is binding though, you must go if you say that. Also, it would be a good idea to contact your interviewer, especially if you two got along, because he/she can speak for you and act as your advocate.
But yeah, you really need to be aggressive and IMHO you must tell them you will go there if accepted. Around June they send out a letter telling you that they've dramatically reduced their waitlist and you are/aren't still in the remaining list of waitlisted students. Later on, they keep cutting it down and that's when I was ultimately rejected.
Just wanted to let you know how things went for me, if you have any questions, feel free to PM.