The Oka varicella vaccine has been tested in clinical trials worldwide in thousands of children. Following licensure in Japan, Korea, Germany, and the United States, the vaccine has been used in several millions of children. The vaccine has been generally well-tolerated with the most common complaints being pain and redness at the injection site and a mild rash following vaccination. The incidence of herpes zoster has not increased in vaccinees and may have decreased. Efficacy rates vary between 65% and 100% depending on the intensity of exposure to natural varicella and the potency of the vaccine. In those few vaccinees who develop MVLS, the rash is generally milder than seen following natural infection (median < 50 versus 300 lesions, respectively, as well as a lower incidence of fever). There has been no evidence to date to indicate waning immunity postvaccination. Studies are in progress in the United States to evaluate whether this will occur and the effect of booster doses of vaccine. It is expected that in countries where there is widespread use of the vaccine in healthy children, disease rates will fall dramatically as will the morbidity and mortality associated with natural varicella in this population.