Background and aims Patients with persistent deficiencies in the complement pathway have an increased risk for meningococcal infection and can experience recurrent disease. In this group we can include genetic deficiencies, functional or anatomic asplenia and complement blocking therapies.

Methods Two patients with atypical hemolytic uremic syndrome confirmed by genetic testing, one with Complement Factor H mutation, Homozygous Risk Haplotype and Hheterozygous Risk Haplotype in MCP, the other one with Anti-CFH Antibodies and Complement Factor H Related Protein 1 and 3 Homozygous Deletions, under long time complement blocking therapy with Eculizumab were vaccinated for Neisseria Meningitidis. We used the two commercially available vaccines in Europe for serotypes A, C, W135, Y and for serotype B.

Results Vaccine reaction was tested after one year by measuring the IgG antibody for Neisseria Meningitidis serotype A, C, W135, Y and B.

In both patients we obtained good vaccine reaction for each Neisseria Meningitidis serotypes with IgG level over the upper laboratory limits.

Conclusions In patients with terminal complement complex deficiency, congenital or acquired, Neisseria Meningitidis vaccination is mandatory.

In Europe, Neisseria Meningitidis serotype B is involved in more than 75% of infections, so vaccination for this strain is important.

Because Complement System is involved in the defense against these bacteria, even if we obtain a good vaccine reaction, we can not be sure if this assures adequate disease protection.

Long time antibiotic prophylaxis and close monitoring of these patients may be required.