This study is about how the medicine **TAK-881** works in people with **Primary Immunodeficiency Diseases (PIDD)**. PIDD means a person has problems with their immune system, which helps fight off sickness. The study compares TAK-881 to another medicine called **HYQVIA**. The study involves two groups: one with people 16 years and older, and another with kids aged 2 to less than 16 years. The older group will try both TAK-881 and HYQVIA, while the younger group will only try TAK-881. Participants need to visit the clinic every 3 or 4 weeks for up to 51 weeks for the older group and 27 weeks for the younger group. **Key Points:**

• **Visit Frequency:** Visits to the clinic every 3 or 4 weeks.
• **Study Duration:** Up to 51 weeks for people 16 and older, up to 27 weeks for those under 16.
• **Medication:** TAK-881 and HYQVIA for older participants, TAK-881 only for younger participants.

Participants must have a stable previous treatment with immune system medicines and meet specific health criteria to join. This is to ensure safety and accurate results.