 Eight of the cases were in Pakistan and 14 in Afghanistan, where genetic typing showed repeated introduction from Pakistan as well as local transmission.In Pakistan, transmission of several genetic lineages of WPV1 seen in 2015 had been interrupted by September 2017, though at least two genetic clusters remain.In spite of a significant drop in detected cases in Pakistan, there was an increase in the percentage of environmental samples that test positive for the polio virus, suggesting gaps in identification of infected individuals.