Abstract: From 2016 to 2018, Brazil faced the biggest yellow fever (YF) outbreak in the last 80 years,
representing a risk of YF reurbanization, especially in megacities. Along with this challenge, the
mass administration of the fractionated YF vaccine dose in a na?ve population brought another
concern: the possibility to increase YF adverse events associated with viscerotropic (YEL-AVD) or
neurological disease (YEL-AND). For this reason, we developed a quantitative real time RT-PCR
(RT-qPCR) assay based on a duplex TaqMan protocol to distinguish broad-spectrum infections caused
by wild-type yellow fever virus (YFV) strain from adverse events following immunization (AEFI)
by 17DD strain during the vaccination campaign used to contain this outbreak. A rapid and more
accurate RT-qPCR assay to diagnose YFV was established, being able to detect even different YFV
genotypes and geographic strains that circulate in Central and South America. Moreover, after testing
around 1400 samples from human cases, non-human primates and mosquitoes, we detected just two
YEL-AVD cases, confirmed by sequencing, during the massive vaccination in Brazilian Southeast
region, showing lower incidence than AEFI as expected.
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