Yellow Fever in Older Adults: An Overlooked High-Risk Population in South American Outbreaks

Abstract Yellow fever (YF) remains a re-emerging public health threat in South America, with recent outbreaks reporting high case-fatality rates. Although transmission has predominantly affected rural and sylvatic populations, mounting evidence indicates that older adults experience disproportionately severe outcomes and mortality. This commentary highlights the elderly as an overlooked high-risk group in the current epidemiological landscape. Age-related immunosenescence, comorbidities, endothelial dysfunction, and reduced hepatic reserve likely amplify the pathophysiological impact of yellow fever virus infection. At the same time, concerns about vaccine-associated adverse events in individuals ≥60 years complicate risk–benefit decision-making, contributing to under-vaccination in this vulnerable population. Delayed diagnosis and shifting eco-epidemiological patterns further exacerbate risk. As South America undergoes demographic aging alongside environmental change, targeted, age-specific strategies, including prioritized vaccination, tailored risk communication, and enhanced surveillance for older adults, are urgently needed to reduce preventable fatalities.