INTRODUCTION
Since the initial outbreak in Wuhan, China, in December 2019, the Coronavirus Disease 2019 (COVID-19) has spread across the world, prompting a global pandemic. The disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was seen as a pulmonary and infectious problem (1).
The other conditions initially identified as risk factors for a severe course of COVID-19 were cardiovascular disease, diabetes, and hypertension. Only later in the process came the realization that kidney disease is a leading risk factor for death. Ultimately, it appeared that the population of patients with chronic kidney disease (CKD), especially those treated with dialysis or transplantation, is one of the highest-risk groups for hospitalization and death (2, 3, 4). Dialysis and transplant patients represent a vulnerable population as all of them suffer from multiple pre-existing medical conditions. COVID-19 causes substantial mortality in both dialysis and kidney transplant population due to their underlying chronic kidney disease and a high prevalence of comorbid conditions such as hypertension, diabetes mellitus, and cardiovascular disease (5, 6). Immunosuppressive treatment is also a precondition for a more severe course of the disease. However, the potential effect of its long-term use is a matter of debate (7, 8). Some argue that the transplant patients might be at a higher risk of severe infection resulting from their impaired immune system, while others speculate that immunosuppressive therapy might be protective as it could address the COVID-19 induced cytokine storm (9, 10, 11, 12, 13).
Large European data became available later, after the first wave. Recent data show that CKD patients are at a higher risk than those with other known risk factors, including chronic heart and lung disease. According to the European Renal Association COVID-19 registry which included 4,298 kidney failure patients, 28-day mortality was 20% in 3,285 patients receiving dialysis and 19.9% in 1,013 recipients of a transplant (7). The ERACODA database (1,073 patients) reported a 28-day case fatality rate of 25% in 768 dialysis patients and 21.3% in 305 kidney transplant recipients during the first wave (5). Other reports based on regional or national registries have also suggested lower mortality in kidney transplant patients than in hemodialysis patients (14, 15).
COVID-19 reported case fatality rates vary greatly between countries owing to differences in public health policy, case ascertainment, and testing capacity. During the pandemic, a substantial number of patients died while waitlisted, due to dramatic reductions in organ donation and transplantation, reaching as high as 80% in some countries of the European Union (4, 16). The early days of the pandemic came with plenty of unknowns affecting the healthcare community’s ability to prepare for and perform transplants. At the beginning, hospitals were limiting surgical procedures to emergencies only in an effort to free up staff for COVID-19 patients and to preserve scarce resources such as personal protective equipment. Testing capacity was also limited. Additionally, there was an effort to avoid the risk of further infections which could arise from admitting more patients into hospitals than necessary. Transplants from deceased donors were limited to urgent situations only; while living donation programs were suspended amid the lockdown and fear of infection. However, it was shown that during the outbreak, the risk of being infected by SARS-CoV-2 was more than 4 times lower for kidney transplant recipients than for hemodialysis patients, mainly because transplant patients can be managed at home, while hemodialysis still mostly takes place in hospital settings (4, 17). In-center hemodialysis patients were at a higher risk for COVID-19 related mortality, independently from the known risk factors such as obesity, ischemic heart disease and lung disease (2). Data from Spain and Italy have shown a 30% mortality of dialysis patients (18, 19). Recently published French data showed that the 30-day Covid-19-related mortality was significantly higher in kidney transplant recipients (KTRs) compared to non-transplant patients (17.9% vs 1.4%, P=0.038) (20).