They have never said there was a cure.
I think what you are talking about is not a cure, its about the potion. they said that the potion was taken to make his transformations easier because they're was no cure. Also the potion wasn't invented when he first got the bite so his transformations in the early years were terrible.
And hermione wouldn't know, to everyone in the wizarding world a cure doesn't exit. J K has said this lots of times.
So what i don't get is, why did J K in the second book mention a cure, but by the third, no cure exists?!?!?