“…However, after two doses of the vaccine an antibody response (anti-spike IgG) is present in 69%-89% of allogeneic HCT 66,68,69,[73][74][75][76][77] and 60%-87% of autologous HCT recipients. 66,76 A third dose improves waning (or absent) antispike antibody responses 59,73,[78][79][80][81][82] and neutralizing antibodies, 59,83 but humoral responses remain low even after a third dose. 59,73,[78][79][80][81][82] Data on neutralizing antibodies and T-cell responses, which are better surrogates for protection from severe COVID-19, are scarce.…”