Use of the Japanese Live Attenuated High-Titer Varicella Vaccine in Pediatric Allogeneic Hematopoietic Stem Cell Transplantation Recipients

Background: Hematopoietic stem cell transplantation (HSCT) recipients carry a high risk of primary varicella and varicella-zoster virus (VZV) reactivation. VZV infections can be fatal, and VZV reactivation can be complicated by postherpetic neuralgia, which worsens the recipients’ post-HSCT quality of life. VZV vaccines may prevent such infections; however, international vaccination guidelines do not recommend VZV vaccination of HSCT recipients because few data regarding safety among HSCT recipients are available. In Japan, we use a high-titer Oka stain vaccine for varicella vaccination and zoster prevention in the elderly; the plaque forming unit (PFU) value of this vaccine is as high as the zoster vaccine used in the U.S. Data regarding the safety of zoster vaccine in HSCT recipients is limited; therefore, we report our experience with this high-titer zoster-equivalent varicella vaccine in pediatric allogeneic HSCT recipients.

Patients and Methods: Forty-seven pediatric allogeneic HSCT recipients who underwent transplantation at the Saitama Children’s Medical Center from 2000-2011 were vaccinated with live vaccines and their antibody titers were evaluated after vaccination. Among the 47 recipients, the Japanese high-titer varicella vaccine was administered to 32 recipients. Since establishing the live vaccine initiation criteria in 2009, allogeneic HSCT recipients were considered as recipients for live vaccines, including the varicella vaccine, if 24 months had passed after HSCT without active chronic GVHD or required immunosuppression. In addition, recipients were required to have a lymphocyte count >1500/μl or CD4 cell count >700/μl if they were <6 years and a lymphocyte count >1000/μl or CD4 cell count >500/μl if they were >6 years, normal phytohemagglutinin response, and serum IgG level >500 mg/dL. Before 2009, time for vaccination depended on each doctor’s judgment. Patients were given a single dose of the Biken varicella vaccine containing a minimum of 23,000 PFUs. We use EIA to measure the antibody titer and defined seropositivity as a titer >6.0. The time to evaluate the antibody titer was not fixed. We retrospectively collected the clinical data of recipients and laboratory data by reviewing the medical records.

Results: The 32 recipients, who received the Japanese varicella vaccine, underwent HSCT at a median age of 5.15 years (range: 0.5-16.4 years) and were vaccinated at a median of 20.65 months (range: 4.8-112.1 months) after HSCT. Twenty and 11 patients had received myeloablative and nonmyeloablative conditioning, respectively. Nine patients received related-donor transplant, of which eight were bone marrow and one was peripheral blood. Twenty-three patients received unrelated-donor transplant, of which 14 were bone marrow and nine were cord blood. Antithymocyte globulin was administered to four patients. Eighteen of the 32 patients (56.3%) were seropositive after vaccination. Of the 26 patients, whose vaccination histories and pre-transplantation histories were available, eight were affected by natural disease, six had been immunized, and 12 had not been immunized. At vaccination, the median lymphocyte count was 3201/μl (range: 817-6630/μl) and the median IgG value was 880 mg/dL (range: 233-1461 mg/dL). There was no significant risk factor associated with vaccine failure. We experienced one case of varicella because of wild type VZV and no cases of zoster after vaccination during a median follow-up period of 4.8 years (range: 0.4-11.3 years); the single patient developed varicella 13 days after vaccination, immediately after an influenza virus infection. Whereas, two cases of varicella and one case of zoster developed before vaccination. Of the other 15 recipients, who did not receive varicella vaccine, three varicella and two zoster developed in three recipients.

Conclusion: We safely vaccinated pediatric allogeneic HSCT recipients with the Japanese high-titer varicella vaccine. This finding could encourage the use in the U.S. of zoster vaccines such as Zostavax^@, which contains similarly high PFUs, and low-titer varicella vaccines such as Varivax^@. However, the efficacy of high-titer varicella vaccines for preventing VZV reactivation in this population remains unclear. Further studies are warranted to elucidate the efficacy and difference between low-titer and high-titer varicella and zoster vaccines.