Objective  To investigate the epidemiological characteristics of SARS-CoV-2 pneumonia in kidney transplant recipients and analyze the risk and protective factors of severe/critical infection with SARS-CoV-2.

  Methods  Clinical data of 468 kidney transplant recipients infected with SARS-CoV-2 were retrospectively analyzed. According to the severity of infection, they were divided into mild SARS-CoV-2 infection recipients (n=439) and SARS-CoV-2 pneumonia group (n=29). Among the 439 mild SARS-CoV-2 infection recipients, 87 recipients who were randomly matched with their counterparts in the SARS-CoV-2 pneumonia group according to sex, age and transplantation time at a ratio of 3∶1 were allocated into the mild SARS-CoV-2 infection group. Twenty-nine recipients in the SARS-CoV-2 pneumonia group were divided into the moderate SARS-CoV-2 pneumonia group (n=21) and severe/critical SARS-CoV-2 pneumonia group (n=8). Baseline data of all recipients were collected. The risk and protective factors of SARS-CoV-2 infection in kidney transplant recipients were identified.

  Results  The proportion of recipients complicated with 2-3 types of complications in the SARS-CoV-2 pneumonia group was higher than that in the mild SARS-CoV-2 infection group, and the proportion of recipients treated with tacrolimus(Tac)+mizoribine+glucocorticoid immunosuppression regimen in the SARS-CoV-2 pneumonia group was lower than that in the mild SARS-CoV-2 infection group, and significant differences were observed (both P<0.05). In 29 kidney transplant recipients with SARS-CoV-2 pneumonia in the SARS-CoV-2 pneumonia group, white blood cells, the absolute values of lymphocytes, eosinophils, total T cells, CD4⁺T cells and CD8⁺T cells, and serum uric acid levels were significantly lower, whereas ferritin levels were significantly higher than the values prior to SARS-CoV-2 pneumonia, and significant differences were observed (all P<0.05). Compared with the moderate SARS-CoV-2 pneumonia group, the proportion of recipients with hypoxemia was higher, the proportion of recipients treated with Tac/ciclosporin (CsA)+mycophenolate mofetil+glucocorticoid immunosuppression regimen was higher, and the proportion of recipients administered with 2-3 doses of SARS-CoV-2 vaccine was lower in the severe/critical SARS-CoV-2 pneumonia group, and significant differences were observed (all P<0.05).

  Conclusions  More complications and immunosuppression regimen containing mycophenolate mofetil are the risk factor for SARS-CoV-2 infection in kidney transplant recipients. Vaccination with SARS-CoV-2 vaccine and immunosuppression regimen containing mizoribine are probably the protective factors for lowering the risk of SARS-CoV-2 infection. The levels of inflammatory cytokines are associated with the severity of SARS-CoV-2 pneumonia.