*Purpose: Solid organ transplant (SOT) recipients are not eligible for live-vaccines, including the measles, mumps and rubella (MMR) vaccine, due to safety concerns on immunosuppression. Consequently, SOT patients not immune to measles prior to transplant remain at lifetime risk of measles infection, which carries a high mortality rate in this population. Measles infections have steadily risen in the United States, with the highest incidence in 20 years reported in 2019. We sought to determine the proportion of patients who were not immune to measles at time of initial pre-transplant evaluation as well as subsequent immunization rates. Additionally, we sought to better characterize this population and identify barriers to immunization prior to transplant.

*Methods: We conducted an observational study of patients over the age of 18, evaluated for SOT at an academic medical center from 2007 to 2017, who had undergone serologic testing for measles as part of a pre-transplant work-up. Patients were identified in an institutional database by relevant ICD9 codes for pre-transplant evaluation with accompanying billing codes for measles serology testing. Patients with negative serologic testing for measles were assessed further for multiple characteristics, including immunity to other viruses, MMR administration, reasons for vaccination deferral, and whether patients were evaluated by the hospital Transplant Infectious Diseases service.

*Results: A total of 3014 individuals who met inclusion criteria were included for analysis with 108 (4%) identified as measles IgG negative at time of initial evaluation. Of these, 35 (32%) subsequently received the MMR vaccine, and 36 patients (33%) did not undergo vaccination (Table 1). Information regarding vaccine administration could not be definitively determined for 37 (34%) individuals. Reasons for not receiving MMR with the relative frequencies are as follows: 10 (28%) had medical conditions necessitating pharmacologic immunosuppression, 16 (44%) were undergoing a second transplant and were on anti-rejection medications; 5 (14%) were deceased or had undergone change in goals of care; 4 (11%) required urgent transplantation and were unable to wait the required four week period after vaccination; and 1 (3%) had an acquired immunodeficiency. For measles seronegative individuals, 65 (60%) were seen by the Transplant Infectious Diseases service who provided recommendations regarding measles vaccination.

*Conclusions: Among patients being evaluated for solid organ transplantation, there remains a small but significant proportion of patients who are measles non-immune during pre-transplant evaluation. Reasons for deferring vaccinations in this population were largely immune compromising conditions. Consultation with Transplant Infectious Diseases specialists may help safely identify ideal candidates for MMR vaccination before transplant.

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