 This is a randomized study designed to evaluate the effect of MCV4 on meningococcal carriage. Several high schools will be randomized into the intervention and control groups. Students in intervention group will receive MCV4 at the beginning of the study, students in the control group will be offered MCV4 after the study completion. Three specimens of throat secretions similar to swabs for Strep throat will be collected from the students enrolled in the study: before vaccination of intervention group students at the start of the school year, 8 weeks post-vaccination, and 9 months post-vaccination at the end of the school year. Questionnaire administered at the time of swabbing will assess potential risk factors for meningococcal carriage. Meningococcal bacteria isolated from the throat specimens will be serogrouped and molecularly typed. Approximately 2,000 students in each group will be needed for the study. Anticipating 35 refusal rate and 25 loss to follow-up, approximately 4,200 high school students will need to be approached in each group. 