In the UK rising disease levels due to Neisseria meningitidis serogroup W clonal complex ST-11 (MenW:cc11) strains led to introduction of conjugate MenACWY vaccination for teenagers. We investigated the impact of immunization on carriage of targeted meningococci by whole genome sequencing of isolates recovered from a cohort of vaccinated university students.
Strain designation data were extracted from whole genome sequence data. Genomes from carried and invasive MenW:cc11 were compared using a gene-by-gene approach. Serogrouping identified isolates expressing capsule antigens targeted by the vaccine.
Isolates with a W: P1.5,2: F1-1: ST-11 (cc11) designation, and belonging to the emerging ‘2013-strain’ of the South American-UK MenW:cc11 sub-lineage, were responsible for an increase in carried group W. A multifocal expansion was evident with close transmission networks extending beyond individual dormitories. Carried group Y isolates were predominantly from clonal complex 23, but showed significant heterogeneity and individual strain designations were only sporadically recovered. No shifts towards acapsulate phenotypes were detected in targeted meningococcal populations.
In a setting with high levels of conjugate MenACWY vaccination, expansion of capsule-expressing isolates from the 2013-strain of MenW:cc11, but not MenY:cc23 isolates, is indicative of differential susceptibilities to vaccine-induced immunity.