I'll share my experience...we vaccinated our first born (long before I knew about vaccination choice) and we were exposed to the wild virus...and he still contracted chicken pox. He had the fever, blisters and the whole nine yards, just as if the shots had not done what it claimed to do. I wound up feeling like if this shot didn't "work" why did I do any of them at all?
Now, three children later and much more educated, my understanding of this particular vaccine and disease is that if my kids get wild CP at a reasonable age, the chances of contracting it later in life are slim, save shingles. The vaccine on the other hand is a commitment to an every 10 year booster PLUS you have a chance to contract shingles or CP at anytime (based on my personal observations and experience).