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

BACKGROUND: Solid organ transplant recipients (SOTRs) are susceptible to severe coronavirus disease 2019 (COVID-19); however, immunogenicity studies of the Omicron variants per vaccination schedules are still lacking. We examined humoral immunogenicity following third-dose mRNA vaccine administration in Korean SOTRs who received primary COVID-19 vaccine series on homologous or heterologous schedules. METHODS: We recruited SOTRs at Severance Hospital from October 27, 2021, to March 31, 2022. Blood samples were collected between 14 days and 5 months after the second and third mRNA vaccine (BNT162b2 or mRNA-1273) doses. SARS-CoV-2 anti-spike IgG titer was analyzed. The neutralization inhibition rate was analyzed using the surrogate neutralization assay for the wild-type, Delta, and Omicron variants. RESULTS: No significant differences existed in the SARS-CoV-2 anti-spike IgG positivity rate between the homologous BNT162b2/BNT162b2/BNT162b2 (85%) and other heterologous groups (83% of ChAdOx1/ChAdOx1/BNT162b2, 90% of ChAdOx1/ChAdOx1/mRNA-1273, and 78% of ChAdOx1/BNT162b2/BNT162b2). No significant difference existed in the neutralization inhibition rates between the four groups for wild-type, Delta, and Omicron variants. Median neutralization inhibition rates against the Omicron variant (2-5%) were significantly lower than those against the wild-type (87-97%) and Delta (55-89%) variants (P < 0.001). CONCLUSIONS: Regardless of the schedule, the neutralization inhibition rate against the Omicron variant was poor; therefore, additional preventive measures are required in such high-risk populations.

Matched Versus Mixed COVID-19 Vaccinations in Korean Solid Organ Transplant Recipients: An Observational Study.

BACKGROUND: Solid organ transplant recipients (SOTRs) are vulnerable to severe coronavirus disease 2019 (COVID-19) and exhibit poor antibody responses to COVID-19 vaccines. Herein, we compared the humoral immunogenicity of a mixed vaccine (ChAdOx1 nCoV-19 [ChAd]/BNT162b2 [BNT]) with that of conventional matched vaccines (mRNA, adenoviral vector [AdV-Vec]) in SOTRs. METHODS: Serum samples were collected at Severance Hospital (Seoul, Korea) between September and October 2021 (14 d-5 mo after COVID-19 vaccination; V2). The severe acute respiratory syndrome coronavirus 2 antispike IgG titer (BAU/mL; ELISA) and neutralization inhibition (percentage; neutralization assay) were compared between vaccination groups overall and stratified by V2 (poststudy vaccination visit) timing. RESULTS: Of the 464 participants, 143 (31%) received mRNA vaccines, 170 (37%) received AdV-Vec vaccines, and 151 (33%) received mixed vaccines (all ChAd/BNT). The geometric mean titer for the ChAd/BNT group was 3.2-fold higher than that of the AdV-Vec group (geometric mean ratio, 3.2; confidence interval, 1.9-5.4) but lower than that of the mRNA group (geometric mean ratio, 0.4; confidence interval, 0.2-0.7). Neutralization inhibition in the ChAd/BNT group was 32%, which was higher than that in the AdV-Vec group (21%; P < 0.001) but lower than that in the mRNA group (55%; P = 0.02). There was no difference in geometric mean titer by V2 timing (ChAd/BNT, 45 versus 31, days 14-60; mRNA, 28 versus 15, days 61-150). CONCLUSIONS: The ChAd/BNT group showed higher humoral immunogenicity than the AdV-Vec group, with similar immunogenicity to the mRNA vaccine. Nevertheless, immunogenicity following the primary vaccination series was poor in all vaccine groups, supporting the justification for booster vaccination in SOTRs.

The feasibility of organ transplantation during the COVID-19 outbreak: experiences from South Korea.

Background: The coronavirus disease 2019 (COVID-19) has forced healthcare systems to reduce transplant activities in order to preserve resources and minimize the risk of nosocomial transmission. Although transplantation societies around the world have proposed interim recommendations, little is known about the safety of transplant surgery under pandemic conditions and how transplant medicine should move forward after the peak of the pandemic. Methods: We describe our experiences regarding the continuation of living and deceased donor transplantation under infection control measures during the COVID-19 outbreak in South Korea. We reviewed consecutive liver and kidney transplantations at Severance Hospital and analyzed national transplantation activities in South Korea. Results: Transplantation activities with living and deceased donors remained stable during the COVID-19 outbreak compared to the same period in 2019. We performed 94 transplantations (58 kidney, 35 liver, and 1 simultaneous liver-kidney) during the COVID-19 outbreak. Twenty-five patients underwent desensitization therapy prior to transplant (nine ABO-incompatible kidney, eight human leukocyte antigen-incompatible kidney, and eight ABO-incompatible liver). No transplant recipients in our center contracted COVID-19. In South Korea, national transplant activities with living and deceased donors remained stable in 2020 compared to 2019. Conclusions: Organ transplantation during pandemics appears to be feasible with appropriate infection prevention measures.