biostudies-literatureKaraba AHNational Institute of Allergy and Infectious DiseasesNational Institute of Diabetes and Digestive and Kidney DiseasesNIDDK NIH HHSNIAID NIH HHSNational Cancer InstituteNCI NIH HHSNIGMS NIH HHS1253-1260https://www.ebi.ac.uk/biostudies/studies/S-EPMC8983554biostudies-literatureUnknown22(4)Vaccine-induced SARS-CoV-2 antibody responses are attenuated in solid organ transplant recipients (SOTRs) and breakthrough infections are more common. Additional SARS-CoV-2 vaccine doses increase anti-spike IgG in some SOTRs, but it is uncertain whether neutralization of variants of concern (VOCs) is enhanced. We tested 47 SOTRs for clinical and research anti-spike IgG, pseudoneutralization (ACE2 blocking), and live-virus neutralization (nAb) against VOCs before and after a third SARS-CoV-2 vaccine dose (70% mRNA, 30% Ad26.COV2.S) with comparison to 15 healthy controls after two mRNA vaccine doses. We used correlation analysis to compare anti-spike IgG assays and focused on thresholds associated with neutralization. A third SARS-CoV-2 vaccine dose increased median total anti-spike (1.6-fold), pseudoneutralization against VOCs (2.5-fold vs. Delta), and neutralizing antibodies (1.4-fold against Delta). However, neutralization activity was significantly lower than healthy controls (p < .001); 32% of SOTRs had zero detectable nAb against Delta after third vaccination compared to 100% for controls. Correlation with nAb was seen at anti-spike IgG >4 Log₁₀ (AU/ml) on the Euroimmun ELISA and >4 Log₁₀ (AU/ml) on the MSD research assay. These findings highlight benefits of a third vaccine dose for some SOTRs and the need for alternative strategies to improve protection in a significant subset of this population.American journal of transplantation : official journal of the American Society of Transplantation and the American Society of Transplant SurgeonsA third dose of SARS-CoV-2 vaccine increases neutralizing antibodies against variants of concern in solid organ transplant recipients.PMC8983554K23 AI157893HHSN272201400007CU01 AI138897R01AI120938S1K23AI157893F32 DK124941T32DK007713R01 AI120938K08AI156021T32 GM136577F32DK124941K08 AI156021K23 DK115908K24 AI144954U54 CA260492K24AI144954K23DK115908U54CA260491T32 DK007713Liang TBlankson JNBailey JRRittenhouse AGAbedon ATRuff JETobian AARAlejo JLAkinde OEby YSitaras IBoyarsky BJGaronzik-Wang JMCox ALWarren DSZhu XThompson EAWang KHKlein SLPekosz ASegev DLKaraba AHWerbel WAfalseA third dose of SARS-CoV-2 vaccine increases neutralizing antibodies against variants of concern in solid organ transplant recipients.Vaccine-induced SARS-CoV-2 antibody responses are attenuated in solid organ transplant recipients (SOTRs) and breakthrough infections are more common. Additional SARS-CoV-2 vaccine doses increase anti-spike IgG in some SOTRs, but it is uncertain whether neutralization of variants of concern (VOCs) is enhanced. We tested 47 SOTRs for clinical and research anti-spike IgG, pseudoneutralization (ACE2 blocking), and live-virus neutralization (nAb) against VOCs before and after a third SARS-CoV-2 vaccine dose (70% mRNA, 30% Ad26.COV2.S) with comparison to 15 healthy controls after two mRNA vaccine doses. We used correlation analysis to compare anti-spike IgG assays and focused on thresholds associated with neutralization. A third SARS-CoV-2 vaccine dose increased median total anti-spike (1.6-fold), pseudoneutralization against VOCs (2.5-fold vs. Delta), and neutralizing antibodies (1.4-fold against Delta). However, neutralization activity was significantly lower than healthy controls (p < .001); 32% of SOTRs had zero detectable nAb against Delta after third vaccination compared to 100% for controls. Correlation with nAb was seen at anti-spike IgG >4 Log₁₀ (AU/ml) on the Euroimmun ELISA and >4 Log₁₀ (AU/ml) on the MSD research assay. These findings highlight benefits of a third vaccine dose for some SOTRs and the need for alternative strategies to improve protection in a significant subset of this population.2022-01-01T00:00:00Z2022 Apr2026-06-06T01:12:59.412Z2025-04-05T18:50:52.546ZS-EPMC89835543495174610.1111/ajt.16933