First Field Use of the Pentavalent Meningococcal Conjugate Vaccine (Men5CV) in Response to a Serogroup C Meningitis Outbreak: Evidence from Yobe State, Northeastern Nigeria

Background: In early 2024, an outbreak of meningococcal meningitis occurred in Yobe State, northeastern Nigeria, prompting an urgent public health response. This study analyzes the epidemiologic, clinical, and laboratory characteristics of the outbreak and evaluates the effect of the reactive Men5C vaccination campaign. Methods: A retrospective review of 2,948 suspected meningitis cases was conducted using line-listed surveillance data for the year 2024. Data included demographic variables, clinical presentation, laboratory results, and vaccination history. Descriptive statistics, bivariate analysis, and multivariable logistic regression were used to identify predictors of mortality. Results: Children and adolescents aged 1–19 years accounted for 84.8% of all cases. The overall case fatality ratio (CFR) was 3.6%, with the highest CFR observed among adults aged ≥ 40 years ( 5.6% ). Males had a significantly higher CFR than females ( 4.4% vs. 2.5%, p = 0.009 ) . Most deaths occurred among individuals who had no record for vaccination against Neisseria meningitidis serogroup A (59.0%). Logistic regression showed that male sex ( aOR = 1.74; 95% CI: 1.14–2.66; p = 0.011 ) and outpatient admission status ( aOR = 0.07; 95% CI: 0.01–0.54; p = 0.010 ) were significant predictors of mortality. Laboratory confirmation identified Neisseria meningitidis serogroup C in 93.8% of all positive cases. A reactive ring vaccination campaign using Men5CV deployed 585,035 doses and administered 579,004 cases across the three most affected local government areas, with vaccination coverage ranging from 45% to 104%. Conclusion: This outbreak was driven primarily by Neisseria meningitidis serogroup C, with adolescents and unvaccinated individuals disproportionately affected. The successful deployment of Men5CV demonstrates its feasibility in emergency settings and highlights the urgent need for preventive routine vaccination in Nigeria’s meningitis belt.