This extension study V72P12E1 will investigate the safety, tolerability and immunogenicity of a fourth (booster) dose of rMenB+OMV NZ at 12, 18 and 24 months of age in subjects previously primed with rMenB+OMV NZ according to two different three-dose immunization schedules in infancy (2, 4 and 6 or 2, 3 and 4 months of age in the parent study V72P12). The study will also explore the bactericidal antibody persistence at 12, 18 and 24 months of age, following the two different immunization schedules, in order to identify the optimal timing for boosting. Two catch-up rMenB+OMV NZ doses will be given to unprimed, naïve toddlers at 12 (subjects enrolled in the control group of V72P12), 18 and 24 months of age (two new cohort of subjects enrolled). These subjects will generate data for assessing the safety and immunogenicity of a two-dose catch-up regimen at these ages, but will also serve as controls for a descriptive comparison of antibody persistence and booster responses for the other groups.