IL9 and COVID-19: Elevated circulating levels of interleukin (IL)-1β, IL-2, IL-6, IL-7, IL-8 (CXCL8), IL-9, IL-10, IL-17, IL-18, IL-22, IL-33, granulocyte-colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon (IFN)-γ, tumor necrosis factor (TNF)-α, chemokine (C-X-C motif) ligand (CXCL)10, monocyte chemoattractant protein 1 (CCL2 or MCP-1), macrophage inflammatory protein 1 (MIP-1)A (CCL3), CX3CL1 and MIP-1B (CCL4) (4, 5) have been reported in patients with COVID-19, particularly in those admitted to the intensive care unit (ICU).