Our previous research on the functional CD4+ and CD8+ memory T cells response in participants administrated by two doses of COVID-19 inactivated vaccine suggested that the structural integrity of whole SARS-CoV-2 of inactivated vaccine might be the key to elicit antiviral CD8+ memory T-cell responses, and Th1 dominated the immune response pathway rather than the traditional Th2 [23]. Here, CD4 is linked to COVID-19.