The purpose of this study is to collect serum samples to evaluate duration of protection for NmVac4-A/C/Y/W-135-DT, based on titers determined by Serum Bactericidal Assay with human complement (hSBA). This assay is used to evaluate immunogenicity of meningococcal vaccines, as a surrogate for efficacy. A titer ≥ 1:8 is considered protective.