Varicella Vaccine Safety: Absence of Evidence Is Not Evidence of Absence

The Korea Disease Control and Prevention Agency (KDCA) and the Ministry of Food and Drug Safety (MFDS) issued multiple press releases about safety concerns on a varicella vaccine product developed by a Korean manufacturer in June 2024, reassuring Korean people by explaining their safety assessment results.1-3 However, it is still unclear as to what kinds of safety concerns were detected as a signal for further evaluation since the KDCA and the MFDS said that the assessment was conducted due to the increase in adverse event reporting without mentioning a specific medical definition of the concern.1 The live attenuated varicella vaccine under the assessment, SKYVaricellaTM, was approved by the MFDS in 2018 and has been used for Korea National Immunization Program in children 12 months to 12 years of age in order to prevent varicella.4