CD4 and COVID-19: Both humoral and cellular immune responses are necessary for vaccine-induced immunity.3 Vaccination stimulates the generation of cross-reactive T-cells, such as CD4+ and CD8+, which enable the immune response to infections such as SARS-CoV-2, mitigating COVID-19 severity.4,5 T-helper (Th) 17 cells, a subset of CD4+ cells, are particularly reactive against pathogens that enter the body through mucosal tissue, including most respiratory and gastrointestinal infections.6 They recruit neutrophils and drive Th1 immunity by releasing interleukin (IL) 17 and antimicrobial peptides.