Tests before the vaccine won approval found similar rates of effectiveness. But researchers were not certain how well those findings would apply to broader use. About 20 states already require chicken pox vaccinations for children starting school or day care. It remains unclear if patients are immune for life or need a booster dose. Seward said the vaccine may eventually prove useful in fighting shingles, a disease caused by the same virus as chicken pox.
Shingles cause a painful skin rash and sometimes chronic pain.