The U.S. Food and Drug Administration has approved Imaavy, also known as nipocalimab-aahu, as the first treatment specifically cleared for warm autoimmune hemolytic anemia. Johnson & Johnson announced the decision on Monday, August 24. It covers adults and patients aged 12 and older who are receiving corticosteroids or have previously received them for the rare, potentially fatal blood disorder.
Warm autoimmune hemolytic anemia develops when immunoglobulin G autoantibodies mistakenly attach to and destroy red blood cells at normal body temperature. The resulting anemia can cause profound fatigue and may be accompanied by blood clots, kidney failure, infection and dependence on transfusions. Johnson & Johnson estimates that about one person in 8,000 lives with the condition and that one to three new cases occur annually per 100,000 people.
Imaavy blocks the neonatal Fc receptor, a protein that normally recycles immunoglobulin G and helps harmful antibodies remain in circulation. Reducing those antibodies is intended to address the disease mechanism while preserving important parts of immune function. The weight-based medicine is delivered by intravenous infusion once every four weeks, according to Reuters and the product information.
The approval followed priority review and relied on the randomized, double-blind, placebo-controlled Phase 2/3 ENERGY trial involving 115 adults. Reuters reported that roughly three times as many Imaavy recipients as placebo recipients achieved a durable hemoglobin improvement after 24 weeks. The study defined that response as hemoglobin above 10 grams per deciliter and an increase of at least 2 grams per deciliter for at least 28 days without rescue treatment.
Company data also showed an average hemoglobin increase of 1 gram per deciliter by the first week and improved fatigue scores at week 24 among treated patients. Those findings indicate a rapid and sustained blood-count response, but the approval does not remove the need for clinical monitoring. Common adverse effects included swelling of the limbs, diarrhea and fever, while prescribing information warns of infections and serious allergic or infusion reactions.
Before this decision, doctors generally relied on corticosteroids, broad immunosuppressants and therapies directed at B cells despite the absence of an FDA-approved medicine specifically for the condition. Imaavy first received U.S. approval in April 2025 for certain antibody-positive patients aged 12 and older with generalized myasthenia gravis. The new indication creates a targeted option, while clinicians must weigh response, infection risk and infusion safety for each patient.
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