I had heard the same thing as Peg re: the length of immunity from the Chickenpox vaccine. I asked my son's dr. about it before he was vaccinated. She said that they had been using the vaccine in Japan for many years and if a booster was necessary they would know it long before my son needed it. Not to sound like it isn't a concern - because if it isn't effective for long enough someone's children will be affected - but, if you have a young child, they aren't in the first generation of receipients and boosters it won't be an issue.