IL9 and COVID-19: Compared with the H1N1 group, 29 cytokines were significantly increased in the COVID-19 group, including CTACK, G-CSF, GM-CSF, GRO-α, HGF, IFN-a2, IL-1α, IL-1β, IL-2ra, IL-5, IL-7, IL-8, IL-9, IL-10, IL-12(p70), IL-12(p40), IL-13, IL-15, IL-17, IL-18, LIF, MIF, MIG, β-NGF, SCGF-β, SDF-1α, TNF-α, TNF-β and VEGF.