Background: Vaccination against varicella zoster (VZV) before kidney transplant (Tx) can help prevent severe disseminated VZV disease in immunosuppressed patients (Pts) post-Tx. Despite confirmation of serologic response to vaccinations pre-Tx, studies have shown loss of humoral immunity post-Tx. Here we assessed the risk factors for losing VZV immunity after pediatric kidney Tx.
Methods: A retrospective analysis of 45 Pts with positive pre-Tx VZV IgG (> 1.09 index) was performed. Pts received induction with either a lymphocyte depleting (LDA: ATG or alemtuzumab) or a non-lymphocyte depleting agent (NLDA: basiliximab or daclizumab) and maintained on mycophenolate mofetil, tacrolimus, with or without corticosteroids. Loss of VZV immunity (VZV IgG < 1.09 index) post-Tx was evaluated based on 1) the induction agent used 2) the number of VZV vaccines (Vx) received prior to Tx, and 3) the interval between last dose of VZV Vx and Tx. 
Results: Median age at Tx was 16.7 yrs (IQR 12.7-18.5); 29 (64.4%) were male; 40 (88.9%) received a deceased donor Tx; and 38 (84.4%) received LDA. Additionally, 34 (75.6%) received two VZV Vx prior to Tx; 10 (22.2%) received their last VZV Vx ≤1 yr prior to Tx. After Tx, 11 (24.4%) Pts lost VZV immunity at a median time of VZV IgG testing at 12.6 mos (IQR 8.8-14.9) post-Tx. Those who lost immunity were younger at the time of transplant, 12.4 yrs (IQR 3.9-17.4) vs. 17.3 yrs (IQR 13.4-19.0) (P=0.004), and more likely to be on steroid-based immunosuppression, 9 (81.8%) vs. 11 (32.4%) (P=0.006). There was no difference in the induction agent used between the two groups (P >0.99). There was an increased risk for losing VZV seropositivity after transplant among those who required 3 or more doses of VZV vaccine to seroconvert prior to Tx (HR 3.81, 95%CI 1.09-13.30, P=0.04). Those who received their VZV Vx <1 yr prior to Tx were more likely to lose post-Tx immunity (Figure 1, P=0.0003). Despite losing immunity, none of the patients developed disseminated VZV.

Conclusion: Pediatric kidney Tx Pts are at risk for losing VZV immunity after Tx, with higher incidences among those who were younger at the time of Tx, on steroid-based immunosuppression, required three or more doses of VZV Vx to seroconvert, or received VZV Vx <1 yr before Tx. Post-Tx VZV serologies should be monitored to identify Pts at high risk for disseminated VZV.