Methods: 602 adolescents and adults aged 15-55 years who had received either MenACWY-CRM (N=301) or MenACWY-D (N=301) 4-6 years earlier, and a control group of vaccine-naïve participants (N=102) were enrolled at 37 centers across the U.S. and 701 overall received a single dose of MenACWY-CRM at Day 1, across study groups. Immunogenicity was evaluated pre-vaccination, either 4 or 6 days post-vaccination (sampling subgroups) and 29 days post-vaccination by serum bactericidal activity assay using human complement (hSBA). After vaccination, all participants were to be monitored for 7 days for reactogenicity, 29 days for unsolicited adverse events (AEs), and 6 months for occurrence of medically-attended events, AEs leading to withdrawal and serious AEs.
Results: Sufficiency of the immune response to a booster dose of MenACWY-CRM was demonstrated as the lower limit of the 1-sided 97.5% confidence interval for percentages of participants with hSBA seroresponse for each serogroup at 29 days post-vaccination was >75%, both in participants primed with MenACWY-CRM and MenACWY-D. Independent of quadrivalent meningococcal vaccine priming, >93% of participants achieved a seroresponse at day 29 post-booster. By day 6 post-booster, >47% of primed participants achieved hSBA titers ≥1:8 for MenA, >87% for MenC, >93% for MenW and >85% for MenY, and by day 29 almost all primed participants had seroprotective titers across all serogroups. Overall, the vaccine was well tolerated across participants in all 3 groups and no safety concerns were raised.
Conclusion: MenACWY-CRM induced robust boosting in adolescents and adults primed with a quadrivalent meningococcal conjugate vaccine 4-6 years earlier, with an acceptable clinical safety profile.
Funding: GSK Biologicals SA
S. Senders, None
S. L. Block, GSK: Research Contractor , Research support .
P. Keshavan, GSK Vaccines: Employee , Salary .
T. Mzolo, GSK Vaccines: Employee , Salary .
M. Pellegrini, GSK Vaccines S.r.l.: Employee and Shareholder , Salary .