CD4 and infection: When blood samples from 37 patients who were hospitalized in the acute phase of COVID-19 were analyzed around 2 weeks after symptoms onset, the number of both spike (S) protein- and nucleocapsid (N)-specific CD4+ T cells with polyfunctionality (IL-2+TNF-α+ and IL-2+IFN-γ+) in patients with mild disease was higher than that in patients with severe infection.