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.