HIV damages the immune system by infecting CD4 cells, white blood cells that help fight infections and protect the body from disease. As CD4 cells die, the immune system becomes weak. Taking anti-HIV drugs slows the ability of the virus to multiply and kill CD4 cells. HIV infected children taking anti-HIV drugs have significant inhibition of HIV growth and significant increases in CD4 cell counts. It is not known to what extent CD4 count increases in HIV infected children translate to functional immune recovery. HIV infected children have typically demonstrated poor serological responses to routine childhood immunizations.