Vitamin D deficiency also has a role in other viral infections, as it is related to the replication of the hepatitis B virus (HBV), contributes to inflammation and oxidative stress in patients with hepatitis C virus (HCV), and impairs CD4 T cell recovery in human immunodeficiency virus (HIV)-infected patients treated with highly active antiretroviral therapy (HAART) [16]. The gene discussed is CD4; the disease is viral infectious disease.