Fig. 6. SARS-CoV-2–specific antibody and T cell responses are enhanced after boost immunization.

(A) RBD-specific binding antibody responses and (B) NAb responses against SARS-CoV-2 variants WA1/2020 (ancestral), B.1.1.7 (alpha), B.1.351 (beta), P.1 (gamma), B.1.617.1 (kappa), and B.1.617.2 (delta) are shown for samples collected at days 0, 14, and 28 after the boost immunization with 5 × 10¹⁰ vp Ad26.COV2.S (n = 10) or Ad26.COV2.S.351 (n = 10). Responses to B.1.1.529 (omicron) are also shown for samples collected on day 28. Antibody responses to WA1/2020 were compared with responses to variants at each time point. Antibody responses against variants from day 0 were compared with responses from day 14 after the boost immunization. (C) Comparisons of peak responses against WA1/2020 after the initial single-shot Ad26.COV2.S immunization and peak responses against WA1/2020, B.1.1.7, B.1.351, P.1, B.1.617.1, and B.1.617.2 after the boost immunization with 5 × 10¹⁰ vp Ad26.COV2.S or Ad26.COV2.S.351 are shown. Box and whisker plots indicate interquartile ranges (boxes), medians (horizontal lines), and range (whiskers). (D) RBD-specific MBCs and (E) T cell responses by pooled peptide IFN-γ ELISPOT assays were measured on samples collected at days 0, 14, and 28 after the boost immunization. B cell responses to WA1/2020 were compared with responses to the beta variant at each time point. B cell and T cell responses against variants from day 0 were compared with responses from day 14 after the boost immunization. Bold horizontal lines and numbers in boxes reflect median values. Dotted lines reflect lower limits of quantitation. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001, two-sided Mann-Whitney tests for comparisons between WA1/2020 group and individual variants at each time point (smaller asterisks), as well as for comparisons between individual variants on days 0 and 14 (larger asterisks reflecting P values for the individual variants compared between two groups). SFU, spot-forming unit.