Yellow Fever Vaccination in Older Adults During the 2024–2025 Outbreak in Colombia: National Safety Surveillance and a Benefit–Risk Perspective

Introduction: Yellow fever re-emerged as a major public health threat in the Americas during 2024–2025, with increasing numbers of cases and deaths, predominantly among unvaccinated individuals. Although the live-attenuated 17D yellow fever vaccine is highly effective, adults aged ≥60 years have an increased risk of serious adverse events following immunization (AEFIs). We assessed the safety profile of yellow fever vaccination in Colombia, with particular emphasis on older adults, and contextualized the observed risks within an epidemic setting characterized by active transmission and high mortality. Methods: We conducted an observational, descriptive study using secondary data from Colombia’s Expanded Program on Immunization and the national VigiFlow pharmacovigilance system. Individuals vaccinated against yellow fever between October 1, 2024, and July 31, 2025, were included. Reported AEFIs were analyzed by severity, sex, and age group. Rates were calculated per 100,000 vaccinated individuals, with 95% confidence intervals, and compared between adults aged ≥60 years and younger individuals. Older adults were further stratified into five-year age groups. Results: Among 3,915,966 vaccinated individuals, 425 AEFIs were reported in 233 unique cases. The overall AEFI rate was 10.85 per 100,000 vaccinated individuals, and the severe AEFI rate was 2.94 per 100,000. Adults aged ≥60 years had substantially higher rates of overall AEFIs than those aged <60 years (54.05 versus approximately 6.1 per 100,000, respectively), corresponding to a rate ratio of 8.8. Severe AEFI rates were 11.90 per 100,000 among adults aged ≥60 years and approximately 2.0 per 100,000 among younger individuals, corresponding to a rate ratio of 6.1. The highest severe-event rate was observed among adults aged 80–84 years, at 49.82 per 100,000. Nine fatal outcomes were reported; following causality assessment, none was considered attributable to the vaccine. Conclusions: Reported AEFIs following yellow fever vaccination were more frequent among adults aged ≥60 years, with a particularly marked increase in the oldest age groups. Nevertheless, the absolute rate of severe events remained low, at approximately 1.2 per 10,000 vaccinated older adults, and no reviewed fatal outcomes were attributed to vaccination. In settings of active yellow fever transmission, vaccination decisions for older adults should therefore be guided by individualized benefit–risk assessment rather than age alone, accompanied by careful screening, active pharmacovigilance, and clear risk communication. Vaccination remains the principal intervention for preventing yellow fever-related deaths.