Root cause analysis of a yellow fever outbreak: user manual and questionnaire

Overview

Resurgent yellow fever outbreaks in endemic regions highlight persistent gaps in population immunity and weaknesses in routine immunization systems, particularly following mass vaccination campaigns. This document presents a user manual and set of questionnaires designed to support the systematic analysis of the root causes of yellow fever outbreaks at district level, with a focus on identifying factors contributing to immunity gaps.

The publication provides a structured, stepwise methodology combining an in-depth outbreak assessment checklist and a data collection tool to investigate vaccination coverage and underlying determinants of low immunity. It includes analysis of outbreak characteristics in terms of time, place, person and transmission patterns, alongside examination of vaccination performance. The tool guides users through preparation, data collection, field investigation and identification of corrective actions, drawing on document review, interviews and structured observations. It analyses causal pathways related to failure to vaccinate and vaccine failure, encompassing policy, provider and user-related factors. Developed through literature review, pilot testing in high-risk countries and expert peer review, it is intended for national immunization programmes, outbreak investigation teams and technical partners, supporting evidence-based planning to strengthen immunization systems and reduce the risk of future outbreaks.