Chronic Spontaneous Urticaria (CSU) is a condition where hives appear on the skin for a long time without an obvious reason. This study is testing a new medicine called barzolvolimab for adults with CSU who still have symptoms even after using regular allergy medicines called H1-antihistamines. The study compares barzolvolimab to a placebo, which is a substance with no active medicine, to see if it helps people feel better.

The study lasts a total of 68 weeks, which includes 4 weeks of screening, 24 weeks of placebo-controlled treatment, 28 weeks of active barzolvolimab treatment, and 16 weeks without treatment. Participants need to be at least 18 years old, have had CSU for at least 6 months, and be on a stable allergy medicine regimen. They also must agree to use effective birth control during and after the study if they can have children.

• The study involves several visits and requires participants to keep a daily electronic diary of their symptoms.
• Participants will be randomly assigned to receive either barzolvolimab or a placebo initially.
• Participants should not have certain other medical conditions or have been vaccinated with live vaccines recently.