This study compared two cities to one another, Baltimore and Philadelphia, after implementation of a beverage tax in Philadelphia. They looked at receipts of all participants for a two week period at pre-tax, 3 months, 6 months, and 12 months. Statistically significant reductions of taxed beverage purchases at 3 and 6 months, but not at 12 months. Further study was recommended. Other studies have proved a beverage tax reduced soda consumption.
TL;DR Soda taxes did not reduce soda purchases 12 months after implementation, although secondary analysis found some reduction