It is a Phase 3 extension of study V72P12E1 (NCT00944034). The main aim of the second extension study is to explore the bactericidal antibody persistence in 4-year-old children after a fourth dose boost of rMenB+OMV NZ or after a two-dose catch-up schedule of rMenB+OMV NZ administered to toddlers as part of their respective vaccination courses in study V72P12E1.