Thirty patients reported receiving a third dose of vaccine. During the initial vaccination, 57% of the 30 patients received 2 doses of the 162b2 vaccine (Pfizer/BioNTech), and 43% received 2 doses of the mRNA1273 vaccine (Moderna). 24 patients had no and 6 had low antibodies against the spike protein at a median of 9 days (IQR, 2 to 33 days) before they received their third dose of vaccine. Patients received the third dose of vaccine a median of 67 days (IQR, 54 to 81 days) after the second dose of their initial vaccine series; 15 patients received the Ad26.COV2.S vaccine (Johnson & Johnson/Janssen), 9 received the mRNA-1273 vaccine (Moderna), and 6 received the 162b2 vaccine (Pfizer/BioNTech). Of the 6 patients with low-positive antibody titers before the third dose, all had high-positive antibody titers after the third dose. In contrast, of the 24 patients with negative antibody titers before the third dose, only 6 (25%) had high-positive antibody titers after the third dose. Two (8%) had low-positive antibody titers, and 16 (67%) remained negative.