The problem is that although the inactivated vaccine provides good protection against severe polio it doesn't seem to work too well at stopping people from spre

The problem is that although the inactivated vaccine provides good protection against severe polio it doesn't seem to work too well at stopping people from spreading the virus, which is not ideal for an elimination program. Presumably this was less of an issue in the developed world because polio spreads mostly through the oral-fecal route and there were already a lot of hygene and infrastructure improvements in developed countries aimed at stopping diseases from spreading that way.