This study looks at how the mpox virus spreads and affects the immune system in people with advanced HIV (a virus that weakens the immune system). The study aims to help us understand how to treat and prevent severe illness in these individuals. Participants will help researchers learn how the immune response and virus activity relate to each other. This includes checking how the virus behaves in the body and how it responds to treatment.

• Participants must be at least 18 years old, have advanced HIV, and be hospitalized due to mpox symptoms.
• The study will monitor the virus and immune system activity over time.
• Participants need to give consent, and some with certain medical conditions might not be eligible.

By joining, you will help researchers find better ways to manage mpox in people with advanced HIV. This study is important for improving treatments and reducing severe illnesses or deaths related to mpox in these patients. Eligibility requires a CD4 count (a type of immune cell) below 200 cells/uL.