Hattori F, et al. – This research work was performed to determine the effectiveness of the Oka/Biken vaccine immediately after implementation of the universal immunization program in Japan. Results revealed that vaccine effectiveness (VE) of one dose of Oka/Biken varicella vaccine was insufficient to control varicella. However, two doses of Oka/Biken varicella vaccine was significant for controlling varicella in Japan.