A weak humoral response to two-doses of SARS-CoV-2 vaccine was observed in solid organ transplant (SOT) patients. Preliminary reports suggested the usefulness of a boost with a third dose. Herein, we report the humoral response in 396 SOT patients (mean age 59 ± 15 years, 65% men) who were given three doses messenger RNA-based vaccine (BNT162b2 vaccine [Pfizer-BioNTech]) (Table S1). Of these, 101 were included in our previous report.3 The two first doses were given one month apart, and the third dose was administered 59 (IQR25-75: 47–67) days after the second dose, that is, once the third dose was recommended by the French National Authority for Health. Anti-SARS-CoV-2 spike protein total antibodies were assessed the day of vaccination before the injection using either the Wantai enzyme-linked immunosorbent assay test (Beijing Wantai Biological Pharmacy Enterprise) (228 patients, 57.6%), or another anti-SARS-CoV-2 spike protein assay (n = 168) (Table S2). According to French law (loi Jardé), anonymous retrospective studies do not require institutional review board approval.