CD4 and infection: A previous study also showed that SARS-CoV-2-specific CD4+ T cells in severe but not mild COVID-19 displayed low avidity.36 In addition, while we observed fewer effector CD8+ T cells in asymptomatic patients than moderate and severe patients at the early stage of the infection, the effector CD8+ T cells in asymptomatic patients expressed a higher level of IFNG but not in severe patient and moderate patients until ten days post-symptoms onset.