A framework to assess the risk of yellow fever emergence

Yellow fever (YF) is a viral hemorrhagic fever transmitted by Aedes aegypti mosquitoes. Symptoms range from mild fever to severe complications such as jaundice and haemorrhages, which can be fatal. Martinique, a French island in the Caribbean, has remained YF-free since 1908. However, the reintroduction of A. aegypti in the 1970s, the limited scope of mandatory vaccination-currently required only for international travellers to endemic areas-and increased connectivity to YF-endemic regions heighten its vulnerability. To inform local preparedness activities, we assessed the risk of YF emergence, defined as introduction and establishment, by looking at vector competence of local native species of A. aegypti in Martinique.

We developed a framework to evaluate YF emergence risk, integrating multiple contributing factors and taking Martinique as a case study. We used reported cases from 2015 to 2022 to estimate the predicted force of infection in endemic countries and map genotype presence in source countries. In addition, we analyzed flight traffic patterns from 2019 to 2022 and computed genotype-specific transmission efficiency by local mosquito populations.

Before 2020, Brazil represented the greatest YF introduction risk due to high passenger volumes. However, the moderate transmissibility of the South America II YF virus strain in Martinique's mosquito populations partially mitigated this risk. The COVID-19 pandemic disrupted global travel, temporarily shifting the risk landscape towards African countries such as Ivory Coast and Cameroon, where the West African strain exhibits higher transmissibility. However, this risk remained limited by the low number of travellers from these regions.

There are growing concerns about the risk of YF introduction and emergence in non-endemic territories like Martinique. Climate change, mosquito adaptability (e.g. egg resistance to desiccation, winter diapause) and intensified global travel drive this risk. This integrative risk assessment framework supports YF emergence prevention and could be applied to other at-risk territories.