Background: Kidney transplant recipients (KTRs) are at risk of coronavirus disease 2019 (COVID-19) complications and mortality. This study examined factors associated with moderate, severe, or critical COVID-19 infection among KTRs during the Omicron-predominant period.
Methods: This single-center retrospective study included KTRs aged ≥18 years diagnosed with COVID-19 between January 1, 2022, and December 31, 2023. Mild infection was defined as symptomatic illness without lower respiratory tract infection (LRTI); moderate infection as LRTI without hypoxia; severe infection as oxygen saturation <94% on room air; and critical infection as respiratory failure, septic shock, or multiple organ dysfunction. We compared the characteristics of KTRs with asymptomatic or mild COVID-19 versus those with moderate to critical disease. Logistic regression analysis was performed to identify factors associated with moderate to critical illness.
Results: Most KTRs (94.4%) had received three or more vaccine doses. Of 603 episodes of COVID-19 infection during the study period, 554 (91.9%) were asymptomatic or mild, while 49 (8.1%) were moderate to critical. Multivariate analysis revealed that older age (adjusted odds ratio [aOR], 1.037; 95% confidence interval [CI], 1.006–1.069) and longer symptom duration before seeking care (aOR, 1.288; 95% CI, 1.155–1.436) were associated with higher odds of moderate to critical disease. Protective factors included receiving a vaccine booster within the past year (aOR, 0.414; 95% CI, 0.212–0.809) and higher glomerular filtration rate (aOR, 0.971; 95% CI, 0.956–0.986).
Conclusions: KTRs should seek care early if infected with COVID-19 and keep their COVID-19 vaccine boosters updated within 1 year of the last dose.

Keywords: COVID-19, SARS-CoV-2, Kidney transplantation, Omicron, Vaccination