Vaccine-induced cell-mediated immunity might be a better surrogate than humoral immunity for protection against respiratory viruses such as influenza in patients with compromised immune responses.23, 24 Cellular immunity has been shown to be crucial for clearance of SARS-CoV-2 and recovery from COVID-19.25, 26 SARS-CoV-2-specific CD4 and CD8 T-cell responses were observed in patients with COVID-19,27 and memory B cells and Tfh cells were identified following recovery. This evidence concerns the gene CD4 and COVID-19.