A long CDC report about the problem of polio from the vaccine.
The polio vaccine is a "weak" virus, and in a tiny percentage, the person given the vaccine has it mutate back to the regular full strength disease. They then give it to others: in the USA this caused a dozen cases a year, which is why your kids get shots (dead virus) not the sugar cube.
despite the higher cost, there is a push to give all kids at least one polio shot with the dead virus: This will let them get partial immunity so the oral virus is killed before it mutates and spreads to grandmom, pregnant mom, or the kids who didn't get the vaccine because the local Mullah is paranoid.
The WHO is hoping to wipe out all polio, like they wiped out smallpox. However, as long as there remains a significant percentage of kids who never got the vaccine, you will see these cases popping up.
Routine immunization services also are being strengthened, and most countries incorporated at least 1 dose of IPV into routine childhood immunization schedules in 2015 (6). This was limited from the planned introduction in all 126 countries that used OPV exclusively for routine immunization because of a global IPV supply shortage. To reduce the risk for iVDPV spread from long-term chronic excretors, maintenance of high levels of routine vaccination coverage will be necessary during the polio endgame.