CD4 and COVID-19: While primary COVID-19 vaccination is a key preventive measure, its effectiveness can be compromised in these populations, particularly in those with very low CD4 counts, primarily due to broader impaired antibody response, including a lower affinity of Anti-Receptor-Binding Domain Immunoglobulin G (Anti-RBD IgG), which is the dominant fraction of SARS-CoV-2 antibodies following infection and immunization, to neutralize the virus [4–8].