This study is about a medicine called TAK-881, which is being tested to see how well it works and how safe it is for people with Primary Immunodeficiency Diseases (PIDD). PIDD is a group of disorders where the body’s defense system doesn't work as well. TAK-881 is given under the skin (subcutaneous) and is being compared to another medicine called HYQVIA.

People who are part of this study will need to come to the clinic every 3 or 4 weeks. Adults and teens 16 years and older might get both TAK-881 and HYQVIA, while younger kids will only get TAK-881. The study lasts up to 51 weeks for older participants and up to 27 weeks for younger ones.

• Participants aged 16+ will try both medicines, while younger kids will only get TAK-881.
• Clinic visits are every 3 to 4 weeks during the study.
• The study lasts up to 51 weeks for older teens/adults and 27 weeks for younger kids.