Natural and vaccine-induced immunity to Neisseria meningitidis serogroup C in asplenic patients with β-thalassemia

Natural and vaccine-induced immunity to meningococcus C (MenC) was evaluated in asplenic adolescents and adults with β-thalassemia. At baseline 19.3% of patients and 22.8% age-matched controls had positive (>2 μg/ml) naturally acquired Men C- specific IgG antibodies; patients had a lower probability of having protective SBA compared to controls (OR = 21, p = 0.012). MenC conjugate vaccine (MCC) induced protective IgG concentrations in 63% of patients and 90.1% of controls. SBA increased significantly post vaccination and there were no differences between patients and controls; however patients had significantly lower IgG concentrations post vaccination compared to controls (4.52 vs 10.94 μg/ml, p < 0.001, respectively). A second dose of MCC given to 11 patients who had received MCC in the past induced higher IgG compared to primary response (p = 0.001). Naturally- and vaccine-induced immunity to MenC is impaired in asplenic β-thalassemics; a second dose of MCC improves vaccine immunogenicity and is essential for their optimal protection.