Introduction: It is well known that SARS-CoV-2 infections are associated with increased mortality in elderly people of the general population, but their impact on transplanted patients still needs to be investigated in depth. We analyzed patient survival in 2,135 kidney transplant recipients with a positive SARS-CoV-2 diagnosis and compared the outcomes to 2,135 matched kidney transplant patients without a SARS-CoV-2 diagnosis.

Materials and Methods: In 2020, the Collaborative Transplant Study (CTS) implemented a Covid-19 questionnaire used by 40 participating centers to send us information on diagnosis and vaccination status of kidney transplant recipients who were infected with SARS-CoV-2 (“infected patients”). We used the large CTS database to identify statistical siblings (“matched controls”) for each infected patient based on the following criteria: The matched control must have been transplanted at the same transplant center and around the transplant year of the infected patient (±5 years) and received the same donor type (living vs. deceased). For 2,135 of a total of 3,109 patients reported with a SARS-CoV-2 diagnosis, statistical siblings could be found. For each matched control, the respective survival time was adjusted by the time between transplantation and the SARS-CoV-2 diagnosis recorded for the corresponding infected patient. Demographics are shown in Figure 1. Multivariable Cox regression analysis was performed to determine the effect of SARS-CoV-2 diagnosis on subsequent 1-year patient survival using various confounders.

Results and Discussion: Kaplan-Meier analysis shows a significant impact of SARS-CoV-2 infection on subsequent patient survival (Figure 2). Overall, patients who were diagnosed with SARS-CoV-2 infection had a 6-fold higher risk of dying during the first year after diagnosis (HR=5.66, 95% CI: 4.59–6.98, P<0.001). Analysis of different subpopulations showed that the effect was similar for different geographical regions (Europe: HR=6.91, 95% CI: 3.74–12.76, P=<0.001; South America: HR=5.48, 95% CI: 4.38–6.85, P<0.001), different age categories in years (<40: HR=6.16, 95% CI: 3.00–12.65, P<0.001; 40–59: HR=7.12, 95% CI: 4.97–10.21, P<0.001; ≥60: HR=4.94, 95% CI: 3.71–6.57, P<0.001), recipient sex (males: HR=5.30, 95% CI: 4.11–6.82, P<0.001; females: HR=6.85, 95% CI: 4.66–10.07, P<0.001). A preliminary analysis of our patient cohort did not reveal a significant protective effect of vaccination on mortality (HR=1.15, 95% CI: 0.89–1.47, P=0.28), but the number of available cases was small.

Conclusion: COVID-19 is commonly believed to affect mainly the elderly. However, our analysis of kidney transplant recipients showed that although higher absolute numbers of deaths were found among older patients, mortality risk associated with SARS-CoV-2 infection was increased in all age groups at a similar extent. Thanks to the ongoing support of the participating centers, the CTS is able to collect more data and will analyse them to confirm the results.