A study published today suggests that the effectiveness of the chicken pox vaccine decreases significantly in the first year after it's given but also notes that most vaccinated children who subsequently came down with the disease had mild illnesses.
A team led by Dr. Marietta Vazquez of the Yale University School of Medicine found that the vaccine was 97 percent effective in preventing chicken pox in the first year after the shot was given, but 84 percent effective two to eight years after it was administered.
This was always the argument against vaccinating children for chicken pox. As is true with several viral diseases, chicken pox is far more dangerous in adults then children. If by vaccinating we've defered infection into adulthood we'll have injured more people than we've helped.