Antibody persistence 3 years after immunization of adolescents with quadrivalent meningococcal conjugate vaccine.

BACKGROUND: A quadrivalent meningococcal conjugate vaccine (MCV-4) is recommended for United States teenagers. The duration of protective immunity is unknown. We investigated serum antibody persistence 3 years after vaccination of adolescents. METHODS: Serum samples from participants of a randomized trial who had received MCV-4 (n=52) or polysaccharide vaccine (MPSV-4; n=48) and from unvaccinated controls (n=60) were assayed for serogroups C, W-135, and Y anticapsular antibody concentrations by use of a radioantigen binding assay and for bactericidal activity (in a human complement assay) and passive protection against serogroup C bacteremia in an infant rat model. RESULTS: A higher proportion of participants in the vaccine groups had protective bactericidal titers (> or =1 : 4), compared with that in the control group (for MCV-4 recipients vs. controls, P<.01; for MPSV-4 recipients vs. controls, P< or =.06). More MCV-4 recipients had W-135 bactericidal titers > or =1 : 4 than did MPSV-4 recipients (P=.01). More MCV-4 recipients had passive protective activity against serogroup C bacteremia than did MPSV-4 recipients (76% vs. 49%; P<.01). The differences in protective activity were largest between participants in the vaccine groups with bactericidal titers <1 : 4 (63% protective in MCV-4 recipients vs. 31% protective in MPSV-4 recipients; P=.01). CONCLUSIONS: Compared with MPSV-4, MCV-4 elicited greater persistence of antibody activity against serogroups C and W-135 at 3 years after vaccination in adolescents. On the basis of passive protection data in an infant rat model, bactericidal titers > or =1 : 4 underestimate protective immunity.