Abstract
Background/Objectives: Despite large-scale measles and rubella (MR) vaccination cam paigns in West Africa, measles outbreaks persist, raising concerns about campaign effec tiveness, coverage, and underlying determinants. This study assesses the impact of MR follow-up campaigns in 12 of 17 West African countries (2024–2025) and examines the factors contributing to post-campaign outbreaks. The main objective of this study is to evaluate the impact of MR campaigns on measles transmission, identify the characteristics of post-campaign outbreaks, and propose strategies to improve campaign effectiveness and accelerate progress toward measles elimination in West Africa. Methods: We conducted a cross-sectional and ecological analytical study to examine spatial and temporal variations based on measles surveillance data from 2024 to 2025, post-campaign coverage surveys (PCCS), district-level outbreak reports, and administrative coverage reports. Trends in measles cases before and after the MMR campaigns were assessed, along with demographic characteristics and spatial analyses of confirmed cases. Results: In 2024, 70.5% (12/17) of countries conducted measles vaccination campaigns, but measles outbreaks increased in 2025 (64 districts in 2024 versus 383 in 2025). Children under five remained the most affected (54%), with 85% of cases being either unvaccinated (57%) or of unknown status (28%). Administrative coverage exceeded 95% in most countries, but measles PCCS re vealed gaps, with only Senegal (93%) and Guinea-Bissau (94%) achieving high verified coverage. No country achieved 95% national MPCC. Conclusions: Suboptimal campaign quality, gaps in immunity beyond target age groups, and unreliable administrative data contributed to the persistence of outbreaks. Recommendations include extending Measles vaccination campaigns to older children (5–14 years), improving preparedness by drawing on experiences from other programs such as polio, standardizing PCCS data survey and Vaccines 2026, 14, 75 https://doi.org/10.3390/vaccines14010075 Vaccines 2026, 14, 75 2 of 12 analysis methodologies across all countries, and integrating Measles vaccination campaigns with other services such as nutrition. Keywords: measles; rubella; vaccination campaigns; epidemics; West Africa; coverage surveys ### 1.1. Global and Regional Burden of Measles Measles remains one of the most contagious and deadly vaccine-preventable human diseases in the world, with a basic reproduction number (R0) of 12 to 18, making it signifi cantly more transmissible than SARS-CoV-2 (R0 2–3) or Ebola virus (R0 1.5–2.5) [1], with around 20 million cases per year and significant mortality among children under five years of age [2]. Despite the availability of a safe and effective measles and rubella (MR) vaccine since 1963, measles caused approximately 140,000 deaths worldwide in 2022, primarily among children under five in low-income countries, and outbreaks continue to occur, particularly in areas with suboptimal vaccination coverage or where supplementary immunization activities (SIAs) are delayed [2]. The African Region accounted for 38% of global cases be tween 2021 and 2023, with West Africa experiencing cyclical outbreaks every 2 to 5 years [3]. The WHO African Region has made substantial progress toward measles elimination, but persistent immunity gaps and uneven campaign quality have hampered sustained success. The Global Vaccine Action Plan (GVAP) aimed for the elimination of measles in five WHO regions by 2020, but only the Americas maintained their elimination status. Africa’s elimination deadline was extended to 2030, but the region reported a 400% increase in cases between 2022 and 2024, with Nigeria alone accounting for 25% of continental cases [4]. This resurgence has been attributed to three main factors: 1. Vaccination gaps: 22 million children worldwide did not receive their first dose of measles vaccine in 2022, with West Africa contributing 3.2 million of these [5]; 2. Disruptions related to COVID-19: 61% of African countries reported postponements of measles vaccination campaigns during the 2020–2021 period, creating an immunity debt [6]; 3. Urban–rural disparities: Coverage in urban slums in West Africa (e.g., Lagos, Abidjan) is 15–20% lower than national averages due to mobility and documentation prob lems [7]. Eliminating Measles Rubella remain a key goal of Immunization Agenda 2030 (IA2030). In 2024, 12 of the 17 countries in the WHO West Africa inter-Country Support Team (IST-WA) conducted measles follow-up campaigns targeting different age groups. However, by mid-2025, measles outbreaks had been observed, raising concerns about the effective ness of these campaigns. Recent studies have questioned the reliability of administrative vaccination coverage data and highlighted the limitations of using national vaccination coverage as the sole predictor of outbreak risk [8]. Furthermore, the data suggest that even countries with coverage > 95% can experience outbreaks due to factors such as delayed campaign timing, poor cold chain management, and waning immunity [9]. Countries with national coverage above 95% may still experience outbreaks due to spatial heterogeneity and pockets of low coverage. This phenomenon has been well documented, including in a landmark study by Gustafson et al. (NEJM, 1987), showing that measles outbreaks can still occur despite vaccine coverage ≥ 95% in school-aged populations [10]. ### 1.2. Vaccination Strategies and Gaps in Evidence WHO recommends 95% vaccination coverage with two doses through routine immunization and community-based vaccination (CBV) to achieve herd immunity. How ever, systematic reviews indicate that the effectiveness of measles vaccination campaigns in Africa is variable. • Temporal immunity: Case–control studies in Niger (2023) showed a vaccine efficacy (VE) of 92% at 6 months after the campaign, decreasing to 78% at 24 months due to decreased immunity in malnourished children [11]; • The limitations of age-based targeting: A meta-analysis of 12 supplementary immu nization activities (2015–2024) revealed that campaigns limited to children under 5 left 28 to 42% of school-aged children vulnerable, thus fueling epidemics among 5- to 14-year-olds [12]; • Data reliability: Administrative coverage overestimates actual protection by 8 to 25% compared to PCCS, as has been documented in Ghana (admin: 97% vs. PCCS: 82%) and Burkina Faso (admin: 95% vs. PCCS: 74%) [13,14]. • Triangulate multiple data streams (surveillance, PCCS, epidemic lineages) to assess the campaign’s impact beyond routine coverage measures [15]; • Assess age-specific immunity gaps through stratified case analysis in 5- to 14-year-olds, a demographic group often excluded from campaign targets; • Propose context-specific solutions, informed by the unique challenges of West Africa (e.g., nomadic populations, conflict zones). ### 1.3. Justification of the Study and Innovation The objective of this study was to: ### 2.1. Study Design and Framework We conducted a cross-sectional and ecological analytical study to examine the spatial and temporal variations in measles epidemics in 17 West African countries from January 2024 to April 2025, focusing on the 12 countries that implemented MMR follow-up cam paigns in 2024. ### 2.2. Data Sources We collected data from the following sources: • Measles surveillance data based on cases (2024–2025); • Laboratory-confirmed cases (IgM+); • Surveillance data: Lists of lines with demographic and vaccination status and epi demiologically linked cases, weekly case reports from the Inter-Country Support Team West Africa surveillance system, etc.; • Vaccination coverage data: Administrative coverage reports of national immunization programs and post-campaign coverage surveys (PCCS); • Surveillance data: Weekly case reports from West African countries surveillance system to WHO inter-Country Support Team; • Epidemic measures: District-level attack rate, age-stratified incidence, spatial cluster ing analysis, etc. All this data is freely accessible on the corresponding websites, which guarantees the confidentiality and ethics of the data, given that it is aggregated. The measles–rubella vaccines used across West African countries during the 2024 follow-up campaigns were WHO-prequalified lyophilized MR vaccines, primarily Serum
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