 Neisseria meningitidis is a leading cause of bacterial meningitis in the United States. A new tetravalent A, C, Y, W-135 meningococcal conjugate vaccine MCV4, MenactraTM manufactured by Sanofi Pasteur Inc. has been approved by Food and Drug Administration FDA in January 2005. This vaccine is recommended by ACIP for routine vaccination of young adolescents at the pre-adolescent visit 11-12 years old, adolescents at high school entry 15 years old, and college freshmen living in dormitories. Prevention of asymptomatic nasopharyngeal carriage of meningococci is important to interrupt person-to-person transmission and to induce herd immunity, when lower transmission results in lower disease rates among those people who are not vaccinated. No studies have yet been done to evaluate the impact of this new vaccine on carriage. 