*Purpose: Assessing serologic status presents opportunities to provide live vaccinations to solid organ transplant (SOT) candidates. This is especially important given the increased risk of infection while taking lifelong immunosuppression. In March 2019, the American Society of Transplantation (AST) Infectious Disease Community of Practice (IDCOP) released updated guidelines for vaccination of SOT patients (pts), which emphasize pretransplant immunity screening. Kidney transplant candidates (KTC) likely have immunity gaps given that end stage renal disease is associated with weakened immune response. This study was conducted to assess baseline serologic status and vaccination practices in KTC

*Methods: This retrospective descriptive study examined serologic data and rates of live vaccination in pts listed for their first kidney transplant (txp) alone at our center from 7/2014-7/2019. Adherence to the AST-IDCOP vaccination guidelines was evaluated. US-born KTC serologies were compared to CDC presumed immunity definitions. After evaluating serologic data for the entire cohort, working backward from 6/2019, 3 subgroups were analyzed further: 100 KTC seronegative (SN) for MMR, all 17 KTC SN for varicella (VZV), and 100 KTC with full immunization records in the electronic medical record (EMR).

*Results: Our study included 672 KTC; 62% were male, median age was 53 years, and 55% were receiving dialysis at time of listing, for 3.48 years on average. In the entire cohort, 17 pts (2.7%) were nonimmune by serology for VZV, while 182 (27.1%) were nonimmune by serology to MMR. The MMR SN group was most commonly SN for mumps (59.9%), followed by measles (49.2%) and rubella (30.8%). Of US-born KTC, 365/372 pts (98.1%) born prior to 1980 were immune to varicella and 159/161 pts (98.8%) born prior to 1957 were immune to measles. Of the SN KTCs, none received VZV vaccination and 6% received MMR vaccination prior to txp. Live vaccines were contraindicated in 2 pts in the VZV group and 15 pts in the MMR group. AST-IDCOP adherence results are listed in Figure 1.

*Conclusions: Most KTC had immune gaps that were not addressed prior to txp with indicated vaccinations. Based on our analysis, CDC presumed immunity definitions can be considered true for KTCs. Limitations of this study include the retrospective design and limited information within the EMR. These findings will guide protocol optimization of vaccination practices, which may increase seroprotection and avoidance of preventable illnesses in KTC and SOT recipients.

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