ISG15 and COVID-19: Type 1 interferon activation has been well established when COVID-19 progresses towards severe pneumonia in longitudinal series, with several markers reported including IFI27, SIGLEC1, OAS1/2, IFI44, IFI44L, ISG15 (Shaath et al. 2020; Krämer et al. 2021; Masood et al. 2021; Khorramdelazad et al. 2022; Xu et al. 2022).