Investigating the contribution of geographic accessibility and vaccine delivery channels to untimely measles vaccination and zero-dose prevalence in The Gambia: implications for disease outbreaks - In 2021 alone, 25 million children globally did not receive the first dose of the diphtheria-tetanus-pertussis-containing vaccine (DTP1). The vast majority of these live in low- and middle-income countries. In addition, many children received their first dose of the measles-containing vaccine (MCV1) much later than scheduled, thus are at significant risk of becoming infected before they are eventually vaccinated and may contribute to suboptimal herd immunity. In The Gambia, there is a recent upsurge of measles, with a 6-fold increase in cases as of mid-2022 compared to 2020 figures despite achieving a minimum MCV1 coverage of 90% over the last decade. Recent data suggest that a large proportion of vaccinations are delayed or not delivered in an age-appropriate manner, according to national vaccination windows. In addition, untimely MCV1 and zero-dose are thought to co-exist and cluster in certain remote communities and may contribute to suboptimal herd immunity. The PI, Dr Oghenebrume Wariri, will apply novel spatiotemporal modelling approaches to map the subpopulation with untimely measles vaccination and zero-dose at fine spatial scale and examine potential links with suboptimal herd immunity and risk of measles outbreaks. He will also examine how geographic accessibility shapes the uptake and delivery of routine vaccination in The Gambia. The project will leverage longitudinal cohort data from Health and Demographic Surveillance Systems in The Gambia, and bio-banked serological samples covering rural populations in the Kiang West District. The integration of these population-based surveillance systems, geospatial data, and serological resources provides a unique scientific opportunity to study the spatial and temporal dynamics of vaccination and population immunity in ways that are not readily achievable in the United States. There are four specific aims for this K43 award: (1) to determine the spatiotemporal pattern of untimely MCV1 and zero-dose children at high spatial resolution in The Gambia; (2) to determine if there is a spatiotemporal relationship between cluster location of untimely MCV1 and measles population immunity; (3) to investigate the contribution of geographic accessibility (between households and vaccination posts, and between fixed and outreach vaccination posts) to zero-dose prevalence and delayed MCV1; and (4) to model geographic access to routine vaccination services to understand the utility of current vaccine delivery channels and identify optimal locations of vaccination clinics and posts. Although conducted in The Gambia, the knowledge generated from this work has direct relevance to American health. Measles outbreaks in the United States are increasingly associated with geographically clustered pockets of under-vaccinated populations. By developing and applying methods to identify, map, and predict such clusters, this project will generate transferable tools to support more precise targeting of vaccination strategies and improve outbreak preparedness in the United States and globally. In addition, insights into how spatial access and service delivery influence vaccination uptake will inform broader efforts to prevent the resurgence of vaccine-preventable diseases globally. This K43 Award will equip Dr Wariri with novel skills and competencies in geospatial and infectious disease modelling, manuscript and grant writing. He will work with a multi-disciplinary mentoring committee comprising internationally recognised African, UK, and US-based experts in vaccinology, population immunity, infectious disease modelling, and geospatial analysis. The proposed research, combined with a structured mentoring and training plan that includes didactic courses and workshops, is designed to facilitate his long-term goal of developing an independently funded research program focused on infectious diseases and spatial epidemiology, consistent with the mission of the Fogarty International Center.
