Beyond Vaccination: Persistent Meningococcal Risk in Anti-C5-Treated aHUS-Case Report and Review of Literature.

Background/Objectives: Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy caused by dysregulation of the alternative complement pathway, often related to genetic mutations or autoantibodies. The introduction of complement C5 inhibitors, such as eculizumab and ravulizumab, has significantly improved renal and overall outcomes. However, complement inhibition impairs host defense against encapsulated bacteria, markedly increasing the risk of invasive infections, particularly Neisseria meningitidis. Vaccination against meningococcal groups ACWY and B, along with temporary antibiotic prophylaxis, is therefore recommended before initiating anti-C5 therapy. Methods: We report the clinical course of a 13-year-old boy with aHUS secondary to anti-complement factor H (CFH) autoantibodies and CFHR3-CFHR1 homozygous deletion, treated with C5 inhibitors. Results: Despite complete meningococcal vaccination and a previous course of antibiotic prophylaxis, the patient developed meningitis during ongoing complement inhibitor therapy. Conclusions: This case highlights that breakthrough invasive infections may occur despite adherence to recommended preventive strategies. It underscores the need for sustained clinical vigilance, timely vaccine boosters, and careful reassessment of the risk-benefit balance of continued complement inhibition therapy.