COVID-19 SARS-CoV-2 infection exhibits a wide inter-individual clinical variability from silent infection to a severe disease and death. To discriminate high-risk patients remains a constant challenge in routine care. The inventors aimed to identify factors influencing the clinical worsening. They analyzed 52 cell populations, 71 analytes and RNA-seq gene expression in the blood in severe patients from the French COVID-19 study upon entering the hospitalization (n=61). In comparison with healthy donors, COVID-19 patients displayed severe abnormalities of 27 cell populations. Unsupervised analysis confirmed the prominent role of the neutrophil activation with high abundance of CD177, a specific neutrophil marker of activation, at the top differentially expressed gene contributing to the clustering of severe patients. Gene abundance correlated with serum levels of CD177 protein. CD177 levels were higher in COVID-19 patients from both the French and a Swiss Cohort “confirmatory” (n=203) cohort as compared to HD (P<0.01), in ICU versus non-ICU patients (P<0.001), and correlated with delay of symptoms onset (P=0.002). Longitudinal measurements revealed that sustained levels of serum CD177 discriminated patients with the worst prognosis leading to death as compared to those who recovered (P= 0.01). The present invention thus relates to the use of CD117 as biomarker of worsening in patients suffering from COVID-19