 This study will answer an important question whether those who are vaccinated are protected not only from disease, but also from being asymptomatic carriers of meningococci. If so, those who are vaccinated will not be able to carry and transmit bacteria to unvaccinated individuals. Meningococcal conjugate vaccines may become available in the near future to other age groups, including infants and children. Determining the efficacy of MCV4 against meningococcal carriage will be important for policy decisions regarding vaccination with this and future conjugate vaccines in different age groups. 