We found that increased serum levels of IL10, a key regulatory cytokine of the immune response, the growth factors GCSF and MCSF, and the innate inflammatory IR mediators IL-6, IL-15, sRAGE, IP10, and MCP3 showed strong prognostic capacity for the progression of severe COVID-19 to ICU admission and/or death. Here, IL15 is linked to COVID-19.