Subjects were previously vaccinated at 15 to 19 years of age with GSK Biologicals' meningococcal vaccine 134612 or with Mencevax™ ACWY. This extension phase starts 18 months after vaccination and part of the subjects will be enrolled in this extension phase. No additional vaccines will be administered during this study and no new subjects will be enrolled. The subjects will have three blood samples taken: at 18, 30 and 42 months after vaccination.