Although IL-6 was equally elevated both in patients with COVID-19 or non-COVID-19 (e.g., influenza), only GM-CSF was prominently elevated in patients with severe COVID-19 (Thwaites et al. 2021), supporting the notion that GM-CSF serves as an important biomarker of COVID-19 disease severity (Hue et al. 2020; Gibellini et al. 2020; Blot et al. 2020; Thwaites et al. 2021; Zhao et al. 2021). Here, CSF2 is linked to COVID-19.