Comparison of median number of influenza-specific infection-elicited and vaccine-elicited cytokine-producing CD4+ and CD8+ T-cells in SOT recipients. SOT: Solid organ transplant; IFN-γ: interferon-γ; TNF-α: tumor-necrosis factor-α; IL: interleukin. Results were expressed as number of vaccine-elicited cytokine-producing CD4+ cells/106 CD4+ T-cells and number of cytokine-producing CD8+ cells/106 CD8+ T-cells. For data presentation, cell frequencies labelled as TNFα+, IFNγ+, IL2+ or IL4+ were cells producing the given cytokine, regardless of the production of other cytokines. The boxes represents the median value. Pre-vaccination frequencies were subtracted from post-vaccination frequencies to highlight vaccine-elicited responses, whereas frequencies at influenza diagnosis were subtracted from frequencies at Day 28 to highlight infection-elicited responses.