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Geographic location of 101 reported chronic and prolonged immunodeficiency-related vaccine-derived poliovirus cases, 1962–2016. Shown by serotype of virus in most recent specimen available: 1 (n = 15), 2 (n = 68), 3 (n = 13), 1 + 2 (n = 2), and 2 + 3 (n = 3).
