Epidemiological and Clinical Characteristics of the Course of COVID-19 Among Vaccinated and Unvaccinated Heart Transplant Recipients in Slovenia

<b>Background</b>: Patients receiving heart transplantation require lifelong immunosuppression and compared to the general population, they have a more than five times higher chance of acquiring COVID-19, and their mortality rates are higher. The aim of the present study was to estimate the epidemiological and clinical characteristics of COVID-19 in heart transplant recipients (HTRs) in Slovenia to estimate the vaccination rate and evaluate possible vaccination-hesitant subgroups. <b>Methods</b>: All SARS-CoV-2-positive HTRs (N = 79) between 1 March 2020 and 31 December 2023 at the Infectious Diseases Department, University Medical Centre Ljubljana, Slovenia, were included retrospectively. Demographic, clinical and vaccination data were extracted from medical documentation and a statistical evaluation was performed. <b>Results:</b> The observed vaccination rate was 63.3%, but among patients who received transplants before the pandemic, it was statistically significantly higher (<i>p</i> = 0.027). Vaccinated HTRs were statistically significantly older (<i>p</i> = 0.004) and had a significantly higher Charlson Comorbidity Index (<i>p</i> = 0.018). Our results indicate no significant differences between vaccinated and unvaccinated HTRs regarding acute respiratory insufficiency (<i>p</i> = 0.135), length of hospital stay (<i>p</i> = 0.106), intensive care unit admission (0.414) and in-hospital mortality (<i>p</i> = 0.317), but we observed statistically more frequently an asymptomatic course in those vaccinated (<i>p</i> = 0.050), and a longer length of stay in vector vaccine recipients (<i>p</i> = 0.011) and in those not re-vaccinated (<i>p</i> = 0.030). There was a significantly higher re-vaccination rate in males (<i>p</i> = 0.005). <b>Conclusions</b>: An asymptomatic course of COVID-19 was more often observed in vaccinated HTRs. Our findings suggest statistically significant differences in COVID-19 vaccine acceptance rates; younger HTRs and those transplanted after the pandemic are more hesitant to vaccinate, while females accept booster doses less frequently.