CD4 and COVID-19: Previous studies of the immune response to COVID-19 have emphasised that CD4, CD8 and lymphocyte depletion are associated with more severe COVID-19 infections.17 Possible explanations for the lymphocyte depletion seen with the disease include sequestration of cytokines and immune cells from blood into the lungs, T-cell exhaustion and viral-induced lymphocyte destruction.17,18