Effectiveness of NmCV-5 vaccine against meningococcal meningitis in an outbreak setting in Niger: results from a case-control study.
BACKGROUND Meningococcal meningitis remains a major public health challenge in Africa's meningitis belt despite the successful elimination of serogroup A epidemics following MenAfriVac introduction. Outbreaks caused by serogroups C, W, and X persist. NmCV-5, a pentavalent conjugate vaccine targeting serogroups A, C, W, Y, and X, was prequalified by WHO in 2023 and used in Niger during reactive vaccination campaigns in 2024. METHODS We conducted a matched case-control study in six health districts in Niger (Niamey IV and Magaria) to estimate NmCV-5 effectiveness against meningococcal meningitis. Cases were individuals with PCR-confirmed meningococcal meningitis, aged 1-19 years, resident in the vaccination campaign area, and presenting with symptom onset ≥10 days post-campaign. Enrollment took place between May 2024 and July 2025. Four age-, sex-, and residence-matched community controls were enrolled per case. Vaccination status was verified by patient-retained vaccination card when available or self-reported. Logistic regression was used to calculate crude and adjusted vaccine effectiveness (VE). RESULTS 17 confirmed cases (14 NmC, 3 NmW) and 68 matched community controls were enrolled in the study. Seven cases (41%) and 58 controls (86%) reported NmCV-5 vaccination; vaccination status of all cases and 8 of 58 (14%) controls was confirmed by vaccination card. Crude VE against all meningococcal meningitis was 88% (95% CI: 62-96), and against NmC specifically was 86% (95% CI: 50-96). Adjusted for household crowding and history of recent respiratory infections, VE was 92% (95% CI: 72-98) overall and 91% (95% CI: 63-98) for NmC. Sensitivity analyses confirmed robustness of estimates under extreme assumptions. CONCLUSIONS NmCV-5 demonstrated high effectiveness against circulating meningococcal strains NmC and NmW in real-world outbreak conditions. Limitations include small sample size, reliance on self-reported vaccination status, and absence of cases from other serogroups. Further studies should assess long-term impact on carriage and effectiveness against invasive disease across all targeted serogroups.