Seroprevalence of Antibodies Against Varicella-Zoster Virus: A Retrospective, Two-Center Study in Varna, Bulgaria

The aim of this study was to assess the age-specific seroprevalence of antibodies against varicella-zoster virus (VZV) in the Varna region of Bulgaria. From January 2017 through December 2024, a total of 5117 individuals were tested for VZV-specific IgG and 4380 for VZV-specific IgM using commercially available ELISA and chemiluminescent immunoassay kits. The overall IgM seroprevalence was 12% (95% CI: 11%–13%), with the highest proportion of IgM-positive samples observed among children aged 1–9 years. IgG seropositivity was detected in approximately 81% of individuals (95% CI: 79%–82%), with the seroprevalence reaching 90% by the age of 40 years. These findings suggest a delayed age of seroconversion and later exposure to VZV compared with patterns observed in the prevaccination era in Europe and underscore the need for reconsideration of current immunization policies in Bulgaria.