The impact of COVID-19 on the duration of the liver transplant process in patients presenting for inpatient liver transplant evaluation

administered as the booster vaccine at 3 months following the second dose.SARS-CoV-2 spike receptor-binding-protein (RBD) IgG was assessed at 1 month, 3 months after the second dose, and 1 month following the booster vaccine.Anti-RBD antibody was tested using electrochemiluminescence immunoassay (Roche Elecsys).According to the basis of plasma-neutralizing capacity in patients with convalescent SARS-CoV-2 infection, anti-RBD titer of <0.8 U/ml, 0.8-50 U/ml, and >50 U/ml were defined as negative, low-positive, and high-positive, respectively.Results: Of 74 LT recipients, 51 (68.9%) were male and median age was 61 (IQR 52-68) years.Median time from transplantation was 5.8 (IQR 2.2-10.8)years.Sixty-one (82.4%) patients were taking tacrolimus, 60 (81.1%) anti-metabolite, and 8 (10.8%) steroids.Fifty-eight (78.4%) patients received AZ/BNT as primary vaccine series.Overall, median anti-RBD titers at 1 month after primary immunization were 609.1 (IQR 38.2-1, 632) U/ml and the levels declined to 397.6 (IQR 77.7-1, 098.5)U/ml at 3 months ( p = 0.54).Antibody reduction rate was comparable between two vaccine platforms (32.1% in AZ/AZ versus 43.8% in AZ/BNT, p = 0.25).After the booster dose, median anti-RBD titers significantly rose to 9, 597.0 (IQR 3, 935-13, 497.5)U/ml ( p < 0.001).The proportion of LT patients with high-positive titers significantly increased from 78.4% at 3 months after primary immunization to 98.6% following the third vaccination ( p <0.001).Patients who received heterologous prime-boost regimen as primary vaccine series had significantly greater anti-RBD levels after the booster (10, 346.0 U/ml in AZ/BNT/Moderna group versus 5, 134.0 U/ ml in AZ/AZ/Moderna group, p = 0.04).(Figure 1) Conclusion: SARS-CoV-2 specific antibody among LT recipients waned over time after primary immunization regardless of vaccine platforms.The booster strategy substantially provided high protective antibody titers in almost all LT patients.Further studies evaluating duration of protection after the booster as well as clinical effectiveness against the variants of concerns are warranted.