Figure. . . Neighbor-joining tree of immunodeficiency-associated vaccine-derived poliovirus isolates from infant, South Africa, 2011. The tree was derived from the viral protein (VP) 1 region and rooted at the Sabin 3 reference strain, showing classification as lineage A or B. South Africa (SOA) isolates are identified by 2 digits indicating year of receipt, 2 digits indicating year of onset of paralysis (11), and 4 digits indicating case number. SOA-11-11-1092 is a representative cerebrospinal fluid sample; SOA-11-11-1099 and SOA-11-11-1093 are representative stool samples. Scale bar indicates nucleotide substitutions per site.