Rise in Group W Meningococcal Carriage in University Students, United Kingdom

MenACWY conjugate vaccination was recently introduced in the United Kingdom for adolescents and young adults to reduce disease from infection by Neisseria meningitidis group W. We conducted a cross-sectional meningococcal carriage study in first-year UK university students. Despite 71% MenACWY vaccine coverage, carriage of group W increased substantially.

university students (8). A catch-up campaign was used to offer MenACWY vaccine to all 14-18-year-old persons, with persons who left school in 2015 (17-18 years of age) given priority.
The rationale for targeting the vaccine to older adolescents and young adults stems from carriage studies showing that this demographic represents the principal reservoir of meningococcal carriage, as well as experience with other polysaccharide conjugate vaccines. Introduction of the MenC monovalent conjugate vaccines previously reduced carriage acquisition of MenC strains in adolescents and young adults (9). There is evidence, albeit limited, to suggest that the quadrivalent vaccine may have a similar effect on carriage of MenCWY strains (10,11). Reduced carriage in this population should lead to indirect protection of other age groups through herd immunity, thus enhancing the public health effect and cost-effectiveness of this approach.

The Study
To assess trends in meningococcal strain carriage, and to determine the immediate effect of the MenACWY vaccine on carriage of MenW/Y strains, we conducted a cross-sectional study in first-year students at the UoN from registration during September 2015 through March 2016. MenACWY vaccination coverage in this student population increased from 31% (preregistration) to ≈70% (immediately postregistration) as a result of a campus-based vaccination campaign targeting freshmen (12).
The study was approved by the Research Ethics Committee at the UoN, and written informed consent was obtained from all participants. We recruited convenience samples of first-year students in September and November 2015 and March 2016. In September, students were recruited during registration; in November and March, students were recruited in 5 dormitories (A-E) with single-occupancy rooms. We searched the UoN Health Service registration database (EMIS Web software; EMIS Health, Leeds, UK) to determine vaccination status in registered first-year students on arrival at the UoN and after the campus-based vaccination campaign.
In September, we obtained pharyngeal swab specimens from eligible students immediately before they received the MenACWY vaccine. We immediately inoculated all pharyngeal swabs onto GC selective agar (Oxoid, Basingstoke, UK) and incubated them at 37°C in air containing 5% CO 2 . After 24 and 48 hours, we

Rise in Group W Meningococcal Carriage in University Students, United Kingdom
Author selected oxidase-positive colonies suggestive of Neisseria spp. and confirmed their identity by amplification of the meningococcal gene crgA plus ctrA and/or porA, as described previously (13). We performed PCR-based genogrouping as described previously (13,14). The Meningococcal Reference Unit, Public Health England, Manchester, UK, performed serogrouping and serotyping of MenW isolates using dot-blot enzyme immunoassay. Sequence data derived from amplified porA and factor H-binding protein alleles was queried against the PubMLST/Neisseria database (http://pubmlst. org/neisseria). We performed χ 2 tests for significance by using STATCALC (Epi Info version 7.2.0.1; Centers for Disease Control and Prevention, Atlanta, GA, USA).
The September sample of 769 first-year students represented 10.9% of the 7,049 first-year students registered in 2015. Carriage rates among this group increased from 14% in late September 2015 to 39% by mid-November 2015 and 46% in March 2016 (online Technical Appendix Table 1, http://wwwnc.cdc.gov/EID/article/23/6/16-1768-Techapp1. pdf). The characteristics of enrolled students and behavioral risk factors for carriage were similar at the 3 time points. The initial carriage rate of 14% was much lower for first-year students in September 2015 than in September 2009 (23.2%; χ 2 = 34, df = 1; p<0.00001) (3), suggesting a reduction in meningococcal carriage in adolescents in the United Kingdom, possibly attributable to an alteration in risk factors for carriage. The MenY carriage rate for incoming students (1.8%) was also lower than that detected in 2009 (2.9%; χ 2 = 2.0, df = 1; p = 0.15) (3).
In September 2015, carriage rates were 4.2% for genogroup capsule null locus (cnl), 3.3% for B, 1.8% for Y, and 0.7% for W strains. A substantial part of the increase in carriage from September 2015 through March 2016 was the result of a notable increase (0.7% to 8.0%) in carriage of MenW strains (online Technical Appendix Table 1). No change in the carriage of MenY strains was detected (online Technical Appendix Table 1). Of the 50 students colonized with MenW, 36 (72%) had received MenACWY vaccine either before or during registration, which is consistent with the overall MenACWY coverage in our firstyear student cohort. Students colonized with MenW at the second and third sampling times were distributed across all 5 dormitories, suggesting widespread dissemination, and 21 (91%) of the MenW carriers in the last time point (March 2016) had been vaccinated at least 5 months before sampling (online Technical Appendix Table 2).
Analysis of the genogroup W isolates showed that 47 (90%) of 52 were serotype 2a (online Technical Appendix Table 1) and harbored alleles for factor H binding protein peptide 22 and PorA P1.5,2, identical to the corresponding alleles harbored by the MenW:ST-11 clone responsible for the increase in invasive MenW disease in the United Kingdom (5). We examined capsular expression by serogrouping and found 32 (62%) of the MenW isolates expressed the W capsular polysaccharide. Of the 21 MenW carriers in March 2016 who had been vaccinated at least 5 months before sampling, 15 (71%) were harboring isolates expressing the W capsule (online Technical Appendix Table 2).

Conclusions
We detected a rapid rise in carriage of MenW among firstyear students in a university setting in the United Kingdom. In comparison, carriage of MenC in adolescents and young adults in the United Kingdom, including in university students, was rare before the introduction of MenC monovalent conjugate vaccines (9). The rise in MenW carriage is most likely due to acquisition within student dormitories or social spaces on campus but was unexpected because no such isolates were found in a similar study at the UoN in 2008-09 (15), and only a limited number in a multicenter carriage study involving UK universities in 2010-11 (6,10).
The increase in MenW carriage among university students merits further monitoring because it could contribute further to the sustained increase in MenW disease in the United Kingdom. Two cases of MenW disease were reported in unvaccinated students in Nottingham during 2015-16. Students attending universities exhibit high mobility and may represent an ongoing vehicle for amplification and spread of MenW into communities throughout the United Kingdom or beyond, with implications for vaccination policy and future research.