CD4 and immunodeficiency disease: As a consequence of these low CD4+ T-lymphocyte percentages in children under 5 years, 35% (38) of 109 children age less than 1 year had values ≤35% for this age group, the WHO threshold for immunodeficiency in HIV-infected children, with 18 meeting the criterion for mild (CD4+ 30% to 35%), 17 for advanced (CD4+ 25% to 29%), and 3 for severe (CD4+ < 25%) immunodeficiency.2