SII, also known as Severe Immune Insufficiency, is a medical condition wherein the immune system is compromised, leaving the body vulnerable to infections and diseases. Some synonyms for SII include Severe Combined Immunodeficiency, Immunodeficiency Syndrome, Primary Immunodeficiency Disorder, and Severe Immunodeficiency. Patients with SII typically require regular medical care and often must take extra precautions to avoid exposure to germs and other potential sources of infection. While treatments may vary depending on the severity and underlying causes of SII, common therapies include immunoglobulin replacement therapy, bone marrow transplants, and antiviral medications to prevent or treat infections. Regular screening and monitoring can help patients manage the condition and maintain their overall health and well-being.