Background As of 2014, routine vaccination strategies in Japan have included the varicella vaccine. Given the widespread use of the vaccine, it is important to investigate the safety profile of the vaccine strain, Oka/Biken varicella, in Japanese patients. Methods Reports of adverse events associated with varicella vaccination between 2005 and 2015 were retrospectively reviewed. Virological analysis was performed on clinical specimens collected from some of the reported cases to determine whether the etiological agent was the wild-type or Oka vaccine–strains. Results There were 351 reports (3.71/100,000 doses) of adverse events during the observation period. Among the 351 reports, there were 88 reports (0.93/100,000 doses) of varicella-like and 66 reports (0.70/100,000 doses) of zoster-like skin rashes. The wild-type strain induced varicella-like skin rashes earlier than the Oka vaccine strain. The Oka vaccine strain induced zoster-like skin rashes in younger patients compared to the wild-type strain. The onset of zoster-like skin rashes after vaccination was earlier in patients vaccinated with the Oka vaccine–type strain. Conclusion The Oka/Biken vaccine is generally safe and well tolerated in Japan. Clinical aspects of adverse reactions caused by the Oka vaccine strain were consistent with previous reports from the United States and Europe.
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