145 kidney transplant recipients who had received their first COVID-19 vaccine, either the Pfizer-BioNTech or Moderna mRNA-1273, only 6.2% (9) showed an antibody response before the second vaccine administration. Seventy-three percent (8) of these patients had total SARS-CoV-2 IgG antibodies, with 8 developing anti-Spike IgG antibody titers ranging from 1:50 to 1:450. No patients demonstrated anti-SARS-CoV-2 Nucleocapsid IgG antibodies. On the contrary, among the 31 waitlisted ESRD patients who received the first vaccine dose, fully 87% produced an antibody response at the time of the second dose.

1011 KT with COVID-19 have been prospectively included in the Spanish Registry and followed until recovery or death. In multivariable analysis, age, pneumonia and KT performed ≤6 months before COVID-19 were predictors of death, whereas gastrointestinal symptoms were protective. Survival analysis showed significant increasing mortality risk in four subgroups according to recipient age and time after KT (age less than 65 years and posttransplant time >6 months, age <65 and time ≤6, age ≥65 and time greater than 6 and age ≥65 and time ≤6): mortality rates were, respectively, 11.3%, 24.5%, 35.4% and 54.5% (p<.001). Patients were significantly younger, presented less pneumonia and received less frequently specific anti-COVID-19 treatment in the second wave (July-December) than in the first one (March-June). Overall mortality was lower in the second wave (15.1 vs. 27.4%, p<.001), but similar in critical patients (66.7% vs. 58.1%, p=.29).

85 postmortem kidney biopsies of COVID patients were evaluated. Severe AKI was present in 54%of patients. Biopsy findings included FSGS in 29%, diabetic nephropathy in 27%, and arteriosclerosis in 81%.Acute tubular injury grades 2–3 were observed in 49%. Histopathologic characteristics were not associated with severe AKI; however, pigment casts on the biopsywere associated with significantly lower probability of kidney function recovery.

242 kidney transplant recipients received their first COVID-19 vaccine with Moderna mRNA-1273. Only 26 (10.8%) KTRs had a positive serology at 28 days post-injection. The median IgG titer was 224 AU/mL (interquartile range: 76−496 AU/mL), whereas the median IgG titer in the seronegative group was < 6.8 AU/mL.