Re-emergence of Yellow Fever Virus in Brazil: Evidence from Forest and peri-urban Settings

Yellow Fever virus (YFV) continues to challenge public health systems across the Americas, despite decades of successful control and the availability of a highly effective vaccine. Following major outbreaks between 2016 and 2022, YFV re-emerged in Brazil in 2023, with a confirmed infection in a non-human primate in São Paulo linked to viral strains circulating in the Midwest region. This reintroduction, combined with increased YFV activity reported across the Americas, signals an ongoing risk of viral persistence and geographic expansion. In this study, we investigate recent YFV dynamics in forest and peri-urban settings, integrating genomic evidence with ecological and spatial data to trace transmission pathways and assess the potential for urban re-emergence. Our findings highlight the need for sustained surveillance in both sylvatic and transitional zones, especially amid fluctuating vaccine coverage and environmental changes that may facilitate spillover events.