Prevalence of VZV Reactivation and Effectiveness of Vaccination with Recombinant, Adjuvanted Zoster Vaccine in Allogeneic Hematopoietic Stem Cell Recipients-A Single-Center Analysis

Background: Secondary immunodeficiencies in allo-HSCT (allogeneic hematopoietic stem cell transplantation) recipients increase the risk of viral reactivation, making vaccinations a vital issue. There is a paucity of data on the use of recombinant vaccine against herpes zoster (RZV) after allo-HSCT. Methods: The analysis included 149 recipients of allo-HSCT, transplanted in 2012-2022, mainly due to hematological malignancies (>95%). RZV was used from 2021 to 2023 according to the current recommendations of ACIP. The ELISA method was used to assess the VZV IgG antibody titers. Results: VZV reactivation was diagnosed in 49 out of 149(33%) patients before vaccination, including 5(3%) patients with reactivation within the first year after transplantation and the remaining 44(30%) within the subsequent three years. At that time majority of patients were not receiving acyclovir prophylaxis. The most common clinical manifestation of reactivation was involvement of intercostal nerves diagnosed in 40(81%) patients. Twenty-one recipients (median age: 41) received two doses of RZV (at median time-34 months after transplantation, range 12-84 months), the majority of them at an interval of 1 month. The serological post-vaccination response was confirmed in 12 recipients with a ratio of 2.38- 8.3 (median 5.095). The median number of total CD3+CD4+cells in vaccinated patients was 451/μl. Despite vaccination, four patients (19%, three with confirmed serological response) developed herpes zoster. Conclusions: Herpes zoster occurred mainly in the late period after allo-HSCT after completion of acyclovir prophylaxis in over 30% of recipients. The preliminary results indicate that RZV vaccination after allo-HSCT is safe but may have limited effectiveness.