I was told it would help prevent them, but that it was still very possible to get them but it should be a milder case.  I got the chicken pox at age 17.  I would say I had at least 1,000 spots.  It was horrible.  Anyway I was never under the impression that my son would not ever get them, but that the shot would help lessen the case.  I hope your little one does okay!  I know its miserable. 

Carrie