 The CDC and corresponding national organizations are carefully observing the failure rate which may be high compared with other modern vaccines—large outbreaks of chickenpox having occurred at schools which required their children to be vaccinated.Prior to the introduction of the vaccine in 1995 in the United States (released in 1988 in Japan and Korea), there were around 4,000,000 cases per year in the United States, mostly children, with typically 10,500–13,000 hospital admissions (range, 8,000–18,000), and 100–150 deaths each year.Though mostly children caught it, the majority of deaths (by as much as 80%) were among adults.