Diabetes and outcomes in yellow fever: an overlooked determinant in a re-emerging threat

Yellow fever (YF) remains one of the most severe arboviral diseases worldwide, with recurrent outbreaks in Africa and South America despite the availability of an effective vaccine (1-4).Epidemics in Brazil between 2016 and 2019 (5), as well as ongoing in 2024-2026 in multiple South American countries, highlighted the persistent vulnerability of unvaccinated populations and the substantial case-fatality rates associated with severe disease (6).While age, viral load, and markers of organ failure are recognized prognostic indicators, the role of chronic metabolic conditions, particularly diabetes mellitus, has received comparatively limited attention.Emerging evidence suggests that diabetes may act as an important amplifier of adverse outcomes in YF, yet this relationship remains insufficiently characterized (7).Chronic non-communicable diseases have been increasingly recognized as modifiers of infectious disease outcomes.In a systematic review and meta-analysis of flavivirus infections, Badawi and colleagues demonstrated that diabetes, hypertension, and obesity were among the most prevalent comorbidities in dengue and West Nile virus infections, and that these conditions were associated with a twofold to fourfold increase in the risk of severe disease (8).Importantly, this comprehensive analysis found that the number of studies addressing yellow fever was insufficient to allow meaningful pooled estimates, underscoring a major evidence gap.This cohort also highlighted the extreme clinical severity associated with fatal cases, including fulminant hepatitis, severe metabolic acidosis, pancreatitis, renal failure,