2722 B. Efficacy and Safety of a Booster Dose of the MenACWY-TT Vaccine Administered 10 Years After Primary Vaccination with MenACWY-TT or MenACWY-PS

BACKGROUND: The quadrivalent meningococcal ACWY polysaccharide tetanus toxoid conjugate vaccine (MenACWY-TT; Nimenrix) is licensed in various countries to prevent disease caused by meningococcal serogroups A, C, W, and Y. In a previous study (NCT00464815), subjects aged 11‒17 years received a primary dose of MenACWY-TT or a quadrivalent polysaccharide vaccine (MenACWY-PS). Here, we report the long-term antibody persistence of the primary dose and the immunogenicity and safety of a booster dose given 10 years after primary vaccination of subjects. METHODS: Participants were enrolled from the Philippines and received a booster dose of MenACWY-TT at 10 years postvaccination. Antibody persistence 10 years postprimary vaccination and immunogenicity 1 month after the booster dose were evaluated by serum bactericidal activity assays using rabbit complement (rSBA) to assess the percentages of subjects with titers ≥ 1:8 and ≥ 1:128 and geometric mean titers (GMTs) for each serogroup. Safety was assessed for the booster dose. RESULTS: Of 229 subjects enrolled in this extension study, 169 and 58 subjects in the MenACWY-TT and MenACWY-PS groups, respectively, completed the booster phase. The percentages of primary MenACWY-TT recipients with prebooster rSBA titers ≥ 1:8 and ≥ 1:128 at year 10 ranged from 71.6%‒90.7% and 64.8%‒85.2% for all serogroups, respectively, compared with 43.1%‒82.4% and 25.5%‒76.5% of primary MenACWY-PS recipients; rSBA GMTs for all serogroups were higher in the MenACWY-TT group than in the MenACWY-PS group at year 10. For the MenACWY-TT and MenACWY-PS groups, respectively, the MenACWY-TT booster dose elicited rSBA titers ≥ 1:8 in 100% and ≥ 98.0% of subjects (figure); 100% and ≥ 96.1% of all subjects had titers ≥ 1:128. For all serogroups, rSBA GMTs at 1 month after the booster dose were higher than before the booster dose. No new safety signals were observed during the booster phase. CONCLUSION: Functional antibody responses elicited by MenACWY-TT persisted 10 years after primary vaccination; the booster dose was well tolerated and elicited robust immune responses. CLINICALTRIALS.GOV: NCT03189745, EudraCT # 2013-001512-29. Funded by Pfizer. [Image: see text] DISCLOSURES: All authors: No reported disclosures.