When Mason kissed Alex in Wizards vs Werewolves, why didn't Alex turn into one??

Didn't you hear this in the episode? It said that that only happens with "mutts", like the girl Justin dated. And apparently Mason was a "purebred"

Alex asks Mason this in Transylvania.

Alex: Hey, I've been meaning to ask you something. I thought when a werewolf kisses a non-werewolf they turn into a werewolf.
Mason: That's only with mutts. I'm a purebred.
Alex: Oh. Did you hear that, Justin? My boyfriend's a purebred!

I think that's all the explanation necessary :D

Mason was a pure bred he said that only happens to mutts.Like when Justin dated Isabella,she was a mutt so when she kissed him he turned into one.

Only girls Werewolves can turn a boy into Werewolves. That is the rule.