A tetravalent meningococcal conjugate vaccine for serogroups A, C, W, and Y (MenACWY) is one of several recommended routine vaccinations for all new U.S. military recruits during enlisted basic training or officer accession training. Military recruits at all basic training centers routinely receive five or more concomitant vaccinations, including combination vaccines, within the first week of arrival at training facilities. While the safety and immunogenicity of coadministered vaccines in infants and children have been widely studied (1-9), the same approach has not been systematically followed for immunizations in adults and, in particular, for meningococcal polysaccharide conjugate vaccines in military personnel.The effects on immunogenicity of concomitant vaccine administration are variable and may be vaccine specific. For example, inactivated polio vaccine (IPV) given alone or coadministered with other vaccines in military personnel showed that seroconversions to polio were more likely when multiple vaccines were administered (10). In contrast, it has been reported that immune response to the concomitant administration of the tetanus-diphtheria-acellular pertussis (Tdap) vaccine and the trivalent influenza vaccine was reported to be noninferior to sequential administration despite lower concentrations of antibody to tetanus, diphtheria, and pertussis toxin components (11, 12). West et al. reported that antibodies to rubella virus and pertussis filamentous hemagglutinin were below predicted levels in healthy adults who received concurrent administration of the bivalent Haemophilus influenzae type b (Hib)-hepatitis B vaccine (HBV) with priming doses of the diphtheria, tetanus, acellular pertussis (DTaP) vaccine and a booster dose of DTaP, oral polio vaccine, IPV, or measles, mumps, and rubella (MMR) vaccine (13). Bar-On et al. carried out a meta-analysis of 18 studies comparing the immune responses to and safety of concomitant and sequential administration of . They reported significantly lower immunological responses to Hib and HBV vaccines and more-localized reactions when these vaccines were coadministered.