How to counter Vex
Let us take a look on how to beat Vex. We will look at champions who are strong against Vex and who are weak against Vex. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Mid champion who counters Vex. You can already win in champion select with the right counters for Vex. If you want to know how to counter Vex then you need to take into account the best picks vs Vex and the worst picks vs Vex. This Vex counter data is based on matches played by Pros on patch 14.21 and previous ones. It is important to see whether Pros counter picked Vex or whether they played as Vex.
Champions used by Pros to counter pick Vex
Looking at the matches from Pros (see table Pros counter picked Vex) we can see that they picked 
Yone most often to counter pick Vex. The matchup Yone vs Vex occured 32 times. Vex has 12 wins and 20 losses in this matchup. Learn how to counter pick Yone to get another perspective on the data.
Lane outcome for Vex
When looking at Vex counters you will notice that win rates alone are not conclusional. Therefore we provide an overview (see table Lane Outcome) where you can see the lane outcome of Pros who played Vex. The lane outcome of Vex consists of three outcomes: Win, Loss or Draw. Let's take a look of Vex lane and match outcome for specific matchups. Considering the lane outcome and the match outcome of a specific matchup, might enable you to find the right counter for Vex.
Conclusion
Analyze the available data and learn how to beat Vex. To master Vex take also a look on Vex builds and runes for Vex. Good luck, Summoner!