Eliminating Measles: Factors That Contribute to Re-Establishing Transmission

Background/Objectives: Since 2016, 14 countries previously verified to have eliminated endemic measles transmission have lost their elimination status. To explore whether there were identifiable risk factors for re-establishing measles transmission in these countries, a narrative review of the literature was undertaken. This identified several potential factors: national vaccination coverage, age at first and second measles-containing vaccine dose, the country's socioeconomic status, surveillance quality, bordering countries endemicity status, supplementary vaccination campaigns just prior to elimination verification, population density, island status, and tourism volume. Methods: World Health Organization (WHO) vaccination and surveillance data were utilized, together with public-facing datasets from the World Bank and the United Nations. An exploratory analysis was undertaken with descriptive epidemiology used for comparing countries where elimination was sustained with those where endemic measles transmission was re-established. Regression modelling was then undertaken with those factors identified as of potential importance. Conclusions: Both descriptive epidemiology and regression modelling indicated that the most important factor is vaccination coverage, although the quality of vaccination coverage estimates from different data sources should be considered. Low-middle income socioeconomic status and bordering endemic countries increased the risk of re-establishment of measles transmission for verified countries. Without coordinated global efforts towards measles eradication, it will be challenging for some countries to maintain elimination.