Safety and Pharmacokinetics of Nirsevimab in Immunocompromised Children

BACKGROUND AND OBJECTIVES Immunocompromised children may have increased risk for severe respiratory syncytial virus (RSV) lower respiratory tract infection (LRTI), potentially leading to prolonged hospitalization, intensive care, and death. The open-label phase II MUSIC trial evaluated the safety and pharmacokinetics of nirsevimab, an extended half-life monoclonal antibody against RSV, in immunocompromised children aged <= 24 months. METHODS Participants received a single intramuscular injection of nirsevimab (first RSV season: 50 mg if <5 kg/100 mg if >= 5 kg; second season: 200 mg). Safety, antidrug antibodies, and pharmacokinetics were evaluated to day 361. RESULTS Participants (n = 100) had >= 1 immunocompromising conditions: primary immunodeficiency (n = 33), previous transplantation (n = 16), HIV infection (n = 8) or treatment with high-dose systemic corticosteroids (n = 29), immunosuppressive chemotherapy (n = 20), or other immunosuppressive therapies (n = 15). Six children experienced eight treatment-related adverse events (none categorized as serious). Three deaths occurred, all were unrelated to treatment. Eleven children, developed antidrug antibodies, with minimal effects on pharmacokinetics and no apparent impact on safety. Nirsevimab serum concentrations at day 151 were similar to those effective in preventing medically attended RSV LRTI in healthy infants. Fourteen children had increased nirsevimab clearance. No protocol-defined medically attended RSV LRTIs occured through day 151. CONCLUSIONS Among immunocompromised children aged <= 24 months, nirsevimab was well tolerated with no safety concerns and serum concentrations were supportive of efficacy. A subset of children with increased nirsevimab clearance, had conditions potentially associated with protein loss; however, the impact on efficacy is unknown.