On the basis that most acute viral infections result in the development of protective immunity [45] and experiences with the 2003 SARS epidemic, researchers hypothesized that CD4+ T cell and neutralizing antibody responses aid in the removal of the acute infection of SARS-CoV-2, and immunological memory against SARS-CoV-2 infection may come from retained T and B cells. Here, CD4 is linked to viral infectious disease.