Figure 3.

Antibody response after three vaccine doses in COVID-19-naive lung transplant recipients (n = 126). (A) Anti-RBD IgG titers expressed in BAU/mL before vaccination (n = 126) and from two weeks to two months after the first (n = 47), the second (n = 54) and the third (n = 126) vaccine doses. (B) Anti-RBD IgG titers before and after the third vaccine doses in the 54 patients with sera available after the second dose. (C) Dynamics of anti-RBD IgG titers expressed in BAU/mL over time after the third vaccine dose (n = 95 additional samples collected from 47 patients during follow-up). (A, B and C) The dotted lines indicate the positivity threshold (7.1 BAU/mL) and the threshold of 264 BAU/mL used in French recommendations to guide prophylactic strategy in immunosuppressed patients. (D) Neutralizing antibody titers assessed by pseudovirus-based assay against D614G, delta and omicron variants in the 47 patients seropositive after the third dose (responders). 22 (46.8%) and 15 (31.9%) sera neutralized the D614G and the delta variants, respectively, but none neutralized the omicron variant. The dotted horizontal black line indicates the cutoff for positivity (1:40 dilution). (E) Spearman correlation between anti-RBD IgG titers and neutralizing antibody titers against D614G (green dots), delta (blue dots) and omicron (orange dots) variants. Green dots are overlapping blue and orange dots on the x axis, and blue dots are overlapping orange dots. The dotted horizontal and vertical black lines correspond to the positivity thresholds of neutralizing antibody titers and anti-RBD IgG titers, respectively. Spearman correlation coefficients (r_S) and p-values related to the neutralization of the D614G mutant and the delta variant were calculated with the Graphpad Prism version 9.3.1. software and depicted in green and blue, respectively. BAU, Binding Antibody Units; ED50, half-maximal effective dilution; RBD, receptor-binding domain. ***p value <0.001.