**Preface to "Solid Organ Transplantation in the Era of COVID-19"**

The impact of COVID-19 on solid organ transplantation was expected to be major since many healthcare systems were struggling to deal with the surges in SARS-CoV-2 infections. This affected routine patient care by limiting resources, had an impact on patient selection and donor organ availability and led to variable evolutions of the patient who had already received a solid organ transplant. The first three articles of this issue deal with the impact of COVID-19 on lung transplant recipients. The first article reports on lung transplant activity in a large Brazilian hospital, showing the challenges and achievements under partially extreme conditions. The second article evaluates the longer-term outcomes of lung transplant recipients who survived COVID-19 in a small sample. Dr. Domingo Franco-Palacios from Detroit presented their experience in a larger series of 64 SARS-CoV-2 infections, reporting a moderately high mortality rate, despite the use of the latest treatments available at the time.

The outcomes of COVID-19 in the unvaccinated liver- and kidney-transplant recipients were studied in 103 consecutive cases by Hailey Hardgrave et al. The classic risk factors known previously, such as hypertension, diabetes and obesity, appeared not to be valid risk factors for the worst outcomes among the transplant recipients; instead, in people over 60 years of age, the use of Belatacept and cylosporine were associated with mortality. Ricardo Wesley Alberca et al., from Brazil, analyzed COVID-19 severity and mortality among liver, heart and kidney recipients and found that the heart and kidney transplant recipients not only had an increase in several COVID-19 severity-associated biomarkers, but also required more intensive care resources and had a higher mortality rate in contrast to liver transplant recipients.

Together with my co-editor Dr. Rene Hage, we summarized the knowledge concerning ´ COVID-19-related lung fibrosis, describing the two different pathways and phenotypes at the time. Previously, weevaluated the potential role of transplant drugs against SARS, MERS and COVID-19 and summarized, in a systematic review, the evidence concerning COVID-19 in patients with solid organ transplantation in April and May 2020. We then described the outcomes of 18 lung transplant recipients with COVID-19 after reporting on our first case; a woman with SARS-CoV-2 and Norovirus Co-Infection.

A multi-system inflammatory syndrome (MIS-C) diagnosis was made in a pediatric heart transplant recipient and his course with prolonged virus detection and lack of IgG response are discussed by Dr. Bibhuti B. Das. Ryan J. Winstead and colleagues examined the influence of remdesivir on the cycle threshold in 30 kidney transplant recipients and were not able to show evidence of a more rapid decline in viral load in those transplant patients who received the drug.

We would like to thank all the authors for their excellent contributions to this topic and are confident that the topics mentioned here will stimulate further research to attempt to understand the best approach to COVID-19 in the context of solid organ transplantation.
