Do I need the retake the writing test on the ACT when I retake the ACT?

I'm wanting to get into Vanderbilt. This was my first time taking the ACT and I made a 29 and an 8 on the writing portion. I'm going to retake the ACT to get in the 30's, but do I need to retake the writing test with it for Vanderbilt? I'm happy with the writing score, but I don't know if it is necessary to retake it or if I only have to take it once for Vanderbilt to accept it.