This study will investigate the long-term protection offered by GSK Biologicals' meningococcal vaccine 134612 up to 3.5 years after vaccination. Subjects were vaccinated at 15 to 19 years of age. This extension phase starts 18 months after vaccination and part of the subjects who were vaccinated in the primary study will be enrolled in this extension phase. No new subjects will be enrolled. This protocol posting deals with objectives & outcome measures of the extension phase 18, 30 and 42 months after vaccination. The objectives & outcome measures of the primary phase are presented in a separate protocol posting (NCT00126945). The Protocol Posting has been updated in order to comply with the FDA Amendment Act, September 2007.