A phase IV, randomized, partially blinded multicenter study to evaluate the safety and immunogenicity of a booster vaccination with GlaxoSmithKline's tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccine, adsorbed [Tdap Boostrix®] co-administered intramuscularly with Aventis-Pasteur's meningococcal (serogroups A, C, Y and W-135) polysaccharide diphtheria toxoid conjugate vaccine (Menactra™) as compared to the administration of either vaccine alone in healthy adolescents 11-18 years of age. "Experimental design: Prospective, randomized, controlled multicenter study with three groups: