CCL4 and COVID-19: A delay in SARS-CoV-2-RNA clearance in the upper respiratory tract during the first days of the disease, higher concentrations of anti-SARS-CoV-2 IgA, IgM, and IgG and of specific cytokines (i.e., IL-6, IL-8 and MIP-1β) at baseline were associated with COVID-19 severity.