Abstract:
Background: Cerebrospinal meningitis (CSM) remains a recurrent epidemic-prone disease across the African meningitis belt, including northwestern Nigeria. Although reactive vaccination campaigns are widely implemented during outbreaks, evidence on their population-level impact on transmission and mortality remains limited. This study evaluated the impact of reactive vaccination on outbreak burden and transmission dynamics in intervention Local Government Areas (LGAs) of Kebbi State, Nigeria.
Methods: We conducted a retrospective spatiotemporal evaluation using routinely collected outbreak surveillance data from Aleiro, Gwandu, and Jega LGAs. Epidemiological indicators, including cases, deaths, attack rates, mortality rates, and case fatality rates (CFRs), were compared between the 2025 outbreak period and the 2026 post-vaccination period. Vaccination activities were conducted over four days, followed by two days of mop-up exercises, achieving 92% administrative coverage (474,462 of 513,052 in the target population) using 487,795 doses of meningococcal conjugate vaccine. Negative binomial regression models assessed changes in transmission intensity and mortality risk, while spatial patterns of case reduction were visualized using choropleth mapping. Statistical analyses were conducted using R version 4.5.2.
Results: A total of 2,471 suspected CSM cases were analyzed across the two years. Reported cases declined from 2,434 in 2025 to 37 in 2026, representing a 98.5% reduction, while deaths decreased from 102 to one death (99.0% reduction). Attack rates declined from 332.1 to 5.0 per 100,000 population, mortality rates from 13.9 to 0.1 per 100,000 population, and CFR from 4.2% to 2.7% (RR = 0.64). Aleiro achieved complete interruption of transmission in 2026, while substantial reductions were observed in Gwandu and Jega LGAs. Negative binomial regression demonstrated a significant reduction in transmission intensity (IRR = 0.02; 95% CI: 0.003–0.068; p<0.001). Spatial analyses showed marked contraction of outbreak hotspots following vaccination. Additionally, serogroup W detected in Aleiro during the 2025 outbreak was not detected during the 2026 season.
Conclusion: Reactive CSM vaccination was associated with substantial reductions in outbreak burden, mortality, attack rates, and transmission intensity across affected LGAs in Kebbi State. The findings support rapid deployment of reactive vaccination as a critical outbreak-control strategy within Nigeria’s meningitis belt and highlight the importance of integrating surveillance, rapid response, laboratory confirmation, and spatial epidemiology into epidemic preparedness frameworks.
Keywords: Cerebrospinal meningitis; Reactive vaccination; Nigeria; Transmission intensity; Serogroup C; Serogroup W.
Biography:
Dr. Ahmad Muhammad Aliyu is a Resident of the Advanced Nigeria Field Epidemiology and Laboratory Training Program (NFELTP). He has extensive experience in outbreak investigation, surveillance system evaluation, vaccine-preventable diseases, spatial epidemiology, and public health emergency response. He has participated in multiple outbreak investigations and surveillance evaluations across Nigeria and has contributed to research on meningitis, cholera, tuberculosis, rabies, and the strengthening of immunization systems.
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