ABSTRACT
BACKGROUND: A fourth dose of SARS-CoV-2 vaccine is recommended in solid-organ transplant (SOT) recipients, but the immunogenicity is poorly known. METHODS: We conducted a retrospective, observational, monocentric study between the 1st January 2021 and 31st March 2022 of the anti-Spike antibody titers after one to four doses of vaccine in SOT. RESULTS: 825 SOT were included. Median age at first vaccine injection was 61.2 (IQR 50.9-69.3) years; 66.7â¯% were male; 63.4â¯% had received four vaccine doses. The proportion of participants with a strong humoral response (>260 BAU/mL) increased with the number of vaccine doses: 10.6â¯% after the 1st dose (D1), 35.1â¯% after the 2nd (D2), 48.5â¯% after the 3rd (D3), and 65.1â¯% after the 4th (D4) (pâ¯<â¯0.001). Among the tested patients, the proportion with a detectable humoral response was significantly higher after D4 than after D3 (47â¯% vs 22â¯%, pâ¯=â¯0.01). Liver transplant recipients had more frequently a strong humoral response after D2, D3 and D4 (ORâ¯=â¯5.3, 3.7 and 6.6 respectively when compared with other organ transplant recipients, pâ¯<â¯0.001). In kidney transplant recipients, belatacept-containing regimen was associated with a lower rate of detectable humoral (9â¯% vs 40â¯%, pâ¯=â¯0.025) after D3, but there was no statistical difference after D4. CONCLUSION: A fourth dose should be proposed to SOT recipients who did not developed an immune response after 3 doses. Kidney transplant recipients receiving belatacept have a poorer, although frequently detectable response.