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Maximum-likelihood trees summarizing sequence relationships among the Sabin 1 OPV strain (root of tree) and the nine type 1 iVDPV isolates across different genomic intervals: (A) P1/capsid region (reference interval for evolution rate calculations), (B) P2/noncapsid region, (C) P3/noncapsid region, and (D) complete ORF. Major diverging lineages are labeled A to E.
