BACKGROUND: Neisseria meningitidis is a leading cause of meningitis and septicemia globally. Recent shifts in serogroup dominance in some settings highlight the desirability of polysaccharide-conjugate vaccines with broader meningococcal coverage than serogroup C vaccines in widespread use. METHODS: We assessed the safety and immunogenicity of a single dose of meningococcal quadrivalent (A, C, W-135, Y) tetanus conjugate vaccine (TetraMen-T), administered at 1 year of age. A total of 378 children were randomized to 1 of 6 groups--5 received alternative formulations of TetraMen-T, the sixth licensed adjuvanted serogroup C conjugate vaccine (Neisvac-C). Solicited adverse event reports were collected from day 0 to 7 after vaccination and unsolicited and serious adverse event reports throughout study participation. Immunogenicity was assessed by serum bactericidal assays containing either a human (hSBA) or baby rabbit (rSBA) complement source before and 1 month after immunization. RESULTS: All vaccine formulations were safe and well tolerated. Using the various measures of immunogenicity, no consistent relationships were observed between the dose of either polysaccharide or carrier and serogroup-specific response for any one antigen. The highest-dose vaccine provided optimal coverage for all 4 serogroups, with the percentage of recipients achieving hSBA titers ≥ 8 against each as follows: A, 92%; C, 96%; W-135, 71%; Y, 82% (corresponding proportions with rSBAs titers >8 all exceeded 90%). The investigational vaccines were less immunogenic against the serogroup C capsular polysaccharide than the licensed comparator. CONCLUSIONS: Studies are ongoing that will help to identify optimal scheduling of quadrivalent meningococcal conjugate vaccines, to facilitate their inclusion into national immunization programs seeking extended serogroup coverage against meningococci. ; Jodie McVernon, Terry Nolan, Peter Richmond, Graham Reynolds, Michael Nissen, Stephen B. Lambert, Helen Marshall, Thomas Papa and Christine Rehm