Limited impact of adolescent meningococcal ACWY vaccination on group

31 Background. In the UK rising disease levels due to Neisseria meningitidis serogroup W 32 clonal complex ST-11 (MenW:cc11) strains led to introduction of conjugate MenACWY 33 vaccination for teenagers. We investigated the impact of immunization on carriage of 34 targeted meningococci by whole genome sequencing of isolates recovered from a cohort of 35 vaccinated university students. 36 Methods. Strain designation data were extracted from whole genome sequence data. 37 Genomes from carried and invasive MenW:cc11 were compared using a gene-by-gene 38 approach. Serogrouping identified isolates expressing capsule antigens targeted by the 39 vaccine. 40 Results. Isolates with a W: P1.5,2: F1-1: ST-11 (cc11) designation, and belonging to the 41 emerging ‘2013-strain’ of the South American-UK MenW:cc11 sub-lineage, were 42 responsible for an increase in carried group W. A multifocal expansion was evident with 43 close transmission networks extending beyond individual dormitories. Carried group Y 44 isolates were predominantly from clonal complex 23, but showed significant heterogeneity 45 and individual strain designations were only sporadically recovered. No shifts towards 46 acapsulate phenotypes were detected in targeted meningococcal populations. 47