Pharmacovigilance assessment of adverse events following yellow fever vaccination: Disproportionality analysis of VAERS reports, 2015–2025

Yellow fever vaccination remains the most effective strategy for preventing infection in endemic and travel-associated settings, yet rare severe adverse events such as viscerotropic and neurotropic disease continue to raise safety concerns. Adverse event reports submitted to the Vaccine Adverse Event Reporting System (VAERS) between 2015 and 2025 were analyzed. Disproportionality algorithms were applied to evaluate reporting patterns, with subgroup analyses by age and sex. The most frequent events were local injection-site reactions and mild systemic symptoms, consistent with clinical trial findings. Severe outcomes, including yellow fever vaccine-associated viscerotropic and neurotropic disease, demonstrated strong disproportionality signals despite their rarity. Additional hypersensitivity-related and less traditional preferred terms were also detected across multiple methods. Female recipients showed higher frequencies of local reactions, while severe events were proportionally more common in older individuals. The analysis reaffirms the established safety profile of yellow fever vaccine while highlighting rare but clinically important severe events and emerging signals. Continued post-marketing surveillance and targeted risk communication remain essential to optimize safe vaccine use.