Epidemic meningococcal meningitis outbreak due to serogroup-c in Yobe state northeastern Nigeria: risk factors and effect of reactive ring vaccination with pentavalent conjugate meningococcal vaccine

Abstract Background There had been a lull in the outbreak of epidemic meningococcal meningitis in Yobe State NE Nigeria for over a decade following the introduction of conjugate monovalent meningococcal vaccine against serogroup-A meningitis. However, an outbreak of serogroup C meningococcal meningitis was recorded for the first time in the state in 2024. Objective to describe the epidemiology of epidemic meningococcal meningitis outbreak due to serogroup C in Yobe State northeastern Nigeria and assess the effectiveness of reactive focused ring vaccination with conjugate pentavalent meningococcal vaccine (Men5) used for the first time in the state and Nigeria in the control of the outbreak. Methodology: cross sectional descriptive epidemiologic study. Results 2,948 cases of epidemic meningococcal meningitis and 72 mortalities (CFR 2.4%) were recorded between March and June 2024 in 12 (70.4%) out of 17 local government areas of the state. The highest incidence and mortality was recorded in the age group 1-20 years [2,547 (86.4%)], 54 (CFR 2.1%)] respectively, and lowest in the age group > 40 years [43 (1.5%), 0 (CFR 0.0%)]. Reactive ring vaccination with Men5 was administered to 581, 025 persons aged 1-30 years. There was a significant declined in both the incidence and mortality due to meningococcal meningitis following focused reactive ring vaccination campaign. Few [223, (0.0038%)] mild adverse events following immunization (e.g. mild to moderate pain or swelling or itching at vaccination site, mild headache, fever etc.) were observed among the vaccinees. Conclusion The epidemic of meningococcal meningitis due to sero-group C had similar clinical and epidemiologic pattern with previous outbreaks due to serogroup A. The used of mass reactive ring vaccination with Men5 focused on affected communities was both effective and safe in controlling the outbreak as well as preventing mortality due to meningitis in Yobe State northeastern Nigeria.