Effect of Bacille Calmette-Guérin vaccination on immune responses to SARS-CoV-2 and COVID-19 vaccination

Abstract

Objectives: Bacille Calmette-Guérin (BCG) vaccination has off-target effects on disease risk for unrelated infections and immune responses to vaccines. This study aimed to determine the immunomodulatory effects of BCG vaccination on immune responses to vaccines against SARS-CoV-2.

Methods: Blood samples, from a subset of 275 SARS-CoV-2-naïve healthcare workers randomised to BCG vaccination (BCG group) or no BCG vaccination (Control group) in the BRACE trial, were collected before and 28 days after the primary course (two doses) of ChAdOx1-S (Oxford-AstraZeneca) or BNT162b2 (Pfizer-BioNTech) vaccination. SARS-CoV-2-specific antibodies were measured using ELISA and multiplex bead array, whole blood cytokine responses to γ-irradiated SARS-CoV-2 (iSARS) stimulation were measured by multiplex bead array, and SARS-CoV-2-specific T-cell responses were measured by activation-induced marker and intracellular cytokine staining assays.

Results: After randomisation (mean 11 months) but prior to COVID-19 vaccination, the BCG group had lower cytokine responses to iSARS stimulation than the Control group. After two doses of ChAdOx1-S, differences in iSARS-induced cytokine responses between the BCG group and Control group were found for three cytokines (CTACK, TRAIL and VEGF). No differences were found between the groups after BNT162b2 vaccination. There were also no differences between the BCG and Control groups in COVID-19 vaccine-induced antigen-specific antibody responses, T-cell activation or T-cell cytokine production.

Conclusion: BCG vaccination induced a broad and persistent reduction in ex vivo cytokine responses to SARS-CoV-2. Following COVID-19 vaccination, this effect was abrogated, and BCG vaccination did not influence adaptive immune responses to COVID-19 vaccine antigens.

Keywords: Bacille Calmette–Guérin (BCG) vaccine; COVID‐19; heterologous; immunity; immunomodulation.

Figure 1

Participant flow diagram and demographics. (a) Consort diagram of samples included in analysis. ^a124 with V0 samples. (b–d) Demographic data on participants with samples collected (b) prior to COVID‐19 vaccination (V0) and (c, d) 28 ± 3 days after the second dose (V2) of (c) ChAdOx1‐S vaccine or (d) BNT162b2 vaccine. BCG, bacille Calmette Guerin; BCOS, BRACE COVID‐19‐specific vaccine sub‐study; NCP, SARS‐CoV‐2 nucleocapsid.

Figure 2

BCG vaccination reduces SARS‐CoV‐2 cytokine responses prior to COVID‐19 vaccination. Whole blood cytokine responses to γ‐irradiated SARS‐CoV‐2 (iSARS) in blood samples taken before COVID‐19 vaccinations (V0). (a) Forest plots depicting adjusted geometric mean ratios (GMR) and 95% confidence intervals for the effect of BCG vaccination determined by multivariable linear regression (Supplementary table 2). GMR > 1.0 indicates responses that were higher for BCG‐vaccinated (n = 70) compared to Control (n = 35) participants. P‐values < 0.05 are depicted in black. (b–d) Unsupervised principal component analysis (PCA) of Z‐scaled iSARS cytokine responses with COMBAT correction for cytokine assay kit. (b) Scree plot of eigenvalues for the first 10 principal components. (c) Heatmap of coefficient of determination (and associated P‐values) for influencing factors for the first 4 PCs. (d) Contribution (loading) for top 10 cytokines contributing to difference in PC1. BCG, bacille Calmette Guérin; HH, household; PC, principal component; WP, workplace.

Figure 3

BCG vaccination does not alter SARS‐CoV‐2 cytokine responses following COVID‐19 vaccinations. Whole blood cytokine responses to γ‐irradiated SARS‐CoV‐2 (iSARS) in blood samples taken 28 days after the second dose of ChAdOx1‐S (purple; BCG group n = 85, Control group n = 33) or BNT162b2 (green; BCG group n = 40, Control group n = 26) vaccination (V2). (a) Forest plots depicting adjusted geometric mean ratios (GMR) and 95% confidence intervals for the effect of BCG vaccination determined by multivariable linear regression. GMR > 1.0 indicates responses that were higher for BCG‐vaccinated compared with Control participants. *P < 0.05. (b–d) Unsupervised principal component analysis (PCA) of iSARS‐induced cytokine responses 28 days after the second dose of ChAdOx1‐S (left) or BNT162b2 (right) vaccination. Prior to PCA, cytokine concentrations were Z‐scaled and PCA was corrected for cytokine assay kit using COMBAT. (b) Scree plot of eigenvalues for the first 10 principal components. (c) Heatmap of coefficient of determination (and associated P‐values) for influencing factors for the first 4 PCs. (d) Contribution (loading) for top 10 cytokines contributing to difference in PC2. BCG, bacille Calmette Guérin; HH, household; PC, principal component; WP, workplace.

Figure 4

BCG vaccination does not alter SARS‐CoV‐2 specific antibody or T‐cell responses to COVID‐19 vaccinations. (a) Dotplot presenting the change in anti‐SARS‐CoV‐2 trimeric Spike Pan‐IgG MFI before (grey) and 28 days after the second ChAdOx1‐S (purple, n = 64) or BNT162b2 (green, n = 60) dose in BCG vaccinated and Control participants. Differences before and after COVID‐19 vaccinations were determined by Wilcoxon signed‐rank test ****P < 0.0001. (b, c) Violin graph with scatter dot‐plot presenting anti‐Spike (S1, S2, RBD and trimeric Spike) and anti‐nucleocapsid (NCP) Pan‐IgG MFI. Differences between BCG‐vaccinated (ChAdOx1‐S n = 47, BNT162b2 = 38) and Control (ChAdOx1‐S n = 17, BNT162b2 n = 22) participants were determined by Wilcoxon rank‐sum test. (d–g) Violin graph with scatter dot‐plot presenting percentage of (d,f) activated and (e, g) cytokine producing (d, e) CD4⁺ and (f, g) CD8⁺ T cells. Differences between BCG‐vaccinated (n = 10) and Control (n = 10) participants were determined by bootstrapped quantile regression. BCG, bacille Calmette Guérin; NCP, nucleocapsid; ns, non‐significant (P ≥ 0.05); RBD receptor binding domain; S1, subunit 1; S2, subunit 2; V0, before COVID‐19 vaccination; V2, 28 days after COVID‐19 vaccination.