Effectiveness of quadrivalent meningococcal conjugate vaccine against meningococcal carriage and genotype character changes: A secondary analysis of prospective cohort study in Korean military trainees.

Objective: We evaluated the changes and molecular epidemiology of meningococcal carriage in military recruits after quadrivalent meningococcal conjugate vaccines (MenACWY) vaccination.
Methods: Oropharyngeal swabs were obtained at the beginning and end of the 5-week training. Carriage rates before and after vaccination were compared to estimate vaccine effectiveness (VE). Cultured isolates were characterized by multi-locus sequence typing (MLST).
Results: Of 866 vaccinated participants, the overall carriage rate was 10.6% prior to MenACWY vaccination and it tended to decrease to 9.5% after 5 weeks of vaccination (P = 0.424). Carriage rate of serogroup ACWY decreased significantly after vaccination (VE _ACWY = 72.6%, 95% CI: 36.3-88.2), and serogroup C was particularly reduced (VE _C = 83.0%, 95% CI: 50.6-94.1), whereas non-groupable isolates increased significantly after vaccination (VE _NG = -76.1%, 95% CI: -176.2 to -13.1). Among 99 carriage isolates with complete MLST profiles, 45 different sequence types with nine clonal complexes (CCs) were identified, and 35.3% of the carriage isolates belonged to hypervirulent strains such as CC-32, CC-41/44, and CC-269.
Conclusions: MenACWY vaccination in military recruits led to reduced carriage rates of serogroups C, W, and Y within a short 5-week period. However, serogroup B isolates belonging to the hypervirulent lineage remained after the implementation of MenACWY vaccination.
Competing Interests: Declarations of competing interest All authors have no conflicts of interest.
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