biostudies-literatureUnknown68Cunha MSWe report the detection of yellow fever virus in Campinas and Ribeirao Preto city areas (two geographic areas within Sao Paulo State, Brazil) from September 2024 to February 2025. Phylogenetic analysis of six new genomes showed a re-introduction in 2022 from Midwest Brazil followed by persistence in Sao Paulo State. Continued surveillance in neotropical primates is required to prevent cases in humans.Revista do Instituto de Medicina Tropical de Sao Pauloe13https://www.ebi.ac.uk/biostudies/studies/S-EPMC12919302biostudies-literatureYellow fever virus resurgence in Sao Paulo State, Brazil, 2024-2025.PMC12919302Manuli ERFernandes NCCAGuerra JMCunha MSFonseca BALDFreitas GDDias JCAPereira GMSabino ECSiconelli MJLValenca INFaria NRMatsumoto PSSfalseYellow fever virus resurgence in Sao Paulo State, Brazil, 2024-2025.We report the detection of yellow fever virus in Campinas and Ribeirao Preto city areas (two geographic areas within Sao Paulo State, Brazil) from September 2024 to February 2025. Phylogenetic analysis of six new genomes showed a re-introduction in 2022 from Midwest Brazil followed by persistence in Sao Paulo State. Continued surveillance in neotropical primates is required to prevent cases in humans.2026-01-01T00:00:00Z20262026-07-16T10:05:06.418Z2026-07-09T10:48:40.213ZS-EPMC129193024171192210.1590/S1678-9946202668013