Meningococcal Carriage Evaluation in Response to a Serogroup B Meningococcal Disease Outbreak and Mass Vaccination Campaign at a College — Rhode Island, 2015

BACKGROUND:  Serogroup B meningococcal disease, caused by the bacterium Neisseria meningitidis, is a rare but severe infection and caused 4 US university outbreaks since 2013. Asymptomatic nasopharyngeal carriage of N. meningitidis is an important source of transmission. MenB-FHbp, a recently-licensed, 3-dose serogroup B meningococcal vaccine, was used to control a 2015 college outbreak in Rhode Island. MenB-FHbp impact on carriage, and potential effect on herd immunity, is unknown and has important vaccine policy implications.

METHODS:  Three cross-sectional carriage surveys were conducted in conjunction with first, second, and third dose MenB-FHbp vaccination campaigns. Questionnaires assessing risk factors for meningococcal disease and carriage and oropharyngeal swabs were collected from undergraduates and graduate students living on-campus. Specimens were evaluated using culture, slide agglutination, real-time PCR, and whole genome sequencing (WGS). Prevalence ratios (PR) were calculated using Poisson regression with general estimating equations for repeat measures.

RESULTS:  Campus-wide vaccine coverage for the 3 MenB-FHbp doses was 97%, 80%, and 77%, respectively. During the first, second, and third surveys, 25%, 24%, and 20% of participants, respectively, carried any meningococcal bacteria. During each survey, 4% carried serogroup B by PCR. Among 2,212 specimens, 0.5% were serogroup C, 0.05% W, 0.1% X, 0.4% Y, and 18% non-groupable N. meningitidis by PCR. WGS did not detect the outbreak strain (serogroup B ST-9069) at baseline. ST-9069 was detected in one student in the second and third surveys, however the strain did not express the serogroup B capsule and was determined to be non-groupable by slide agglutination. 508 students participated in multiple surveys: 370 (73%) remained non-carriers, 36 (7%) cleared carriage, 72 (14%) remained carriers, and 28 (6%) acquired carriage. During the evaluation, 12 students acquired serogroup B carriage: 7 after one MenB-FHbp dose and 5 after two MenB-FHbp doses. Overall, smoking (PR 1.8, 95% confidence interval [CI] 1.5–2.1) and male sex (PR 1.3, 95% CI 1.1–1.6) were associated with increased meningococcal carriage.

CONCLUSIONS:  Despite high MenB-FHbp vaccination coverage, carriage prevalence on campus remained stable over time, suggesting two doses of MenB-FHbp do not rapidly reduce meningococcal carriage or prevent serogroup B carriage acquisition. However, vaccination remains the most important measure to protect individuals against meningococcal disease during outbreaks. Molecular testing is ongoing and a final survey is planned for February 2016. This study will improve our understanding of carriage dynamics over time and provide important data for policymakers considering routine serogroup B meningococcal vaccination programs.