Korean J Transplant.  2022 Nov;36(Supple 1):S16. 10.4285/ATW2022.F-0936.

Comparison of humoral immunogenicity in solid organ transplant recipients after third-dose mRNA vaccine with homologous or heterologous schedules: an observational study

  • 1Department of Pediatrics, Severance Hospital, Yonsei University College of Medicine, Seoul, Korea
  • 2Department of Surgery, Severance Hospital, Yonsei University College of Medicine, Seoul, Korea
  • 3Division of Biostatistics, Department of Biomedical Systems Informatics, Severance Hospital, Yonsei University College of Medicine, Seoul, Korea


Solid organ transplant recipients (SOTRs) are susceptible to severe coronavirus disease 2019 (COVID-19) and im-munogenicity studies of Omicron variants according to vaccination schedules are lacking. We examined the humoral immuno-genicity following third-dose mRNA vaccine administration in Korean SOTRs who received primary COVID-19 vaccine series on a homologous or heterologous schedule.
We recruited SOTRs at the Severance Hospital from October 27, 2021, to March 31, 2022. Blood samples were col-lected between 14 days and 5 months after the second and third mRNA vaccine (BNT162b2 or mRNA-1273) doses. The SARSCoV-2 anti-spike IgG titer was analyzed using an enzyme-linked immunosorbent assay (cut-off <7.1 BAU/mL), and the neutral-ization inhibition rate was analyzed using the surrogate neutralization assay (cut-off <30% of inhibition) for the wild-type, Delta, and Omicron variants.
Overall, 148 participants were included. About 30% participants (n=45) received ChAdOx1/BNT162b2/BNT162b2, 24% (n=36) ChAdOx1 nCoV-19/ChAdOx1 nCoV-19/BNT162b2, 22% (n=33) BNT162b2/BNT162b2/BNT162b2, 20% (n=29) ChAdOx1/ ChAdOx1/mRNA-1273, and 3% (n=5) received other regimens. No significant differences existed in the SARS-CoV-2 anti-spike IgG positivity rate obtained between the homologous BNT162b2/BNT162b2/BNT162b2 (85%) and the other heterologous groups (83% of ChAdOx1/ChAdOx1/BNT162b2, 90% of ChAdOx1/ChAdOx1/mRNA-1273, and 78% of ChAdOx1/BNT162b2/BNT162b2). There was no significant difference in the neutralization inhibition rate between the four groups for wild-type, Delta, and Omicron variants. The median neutralization inhibition rates against Omicron were 25%, significantly lower than those against wild-type (87%–97%) and Delta (55%–89%) (P<0.001).
Heterologous COVID-19 vaccinations, comprising a third-dose mRNA vaccine, showed similar humoral immunoge-nicity compared to homologous BNT162b2/BNT162b2/BNT162b2. Regardless of the schedule, the neutralization inhibition rate against Omicron was very low; therefore, additional preventive measures are required in such high-risk populations.

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