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 ( >= 1: 4), compared with that in the control group (for MCV-4 recipients vs. controls, P < .01; for MPSV-4 recipients vs. controls P <= .060. More MCV-4 recipients had W-135 bactericidal titers >= 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 >= 1: 4 underestimate protective immunity.