The theory goes that if you show symptoms consistent of polio the doctors say “have you been vaccinated?” If you haven’t then they say “must be polio” and if you have they say “well it can’t be polio, must be something else.”
In this case they called it "nonpolio accute flaccid paralysis" instead. This paper found incidence correlation with vaccination rates (more vaccines, more NPAFP):
"NPAFP increased with the number of oral polio vaccine (OPV) doses used (R2 = 25.02%; P < .001). When effect of cumulative doses over the previous years was examined, the NPAFP rate in 2013 best correlated with the cumulative doses received in the previous 7 years (R2 = 57.16%), with 2012 excluded because data for this year were incomplete. This correlation was highly significant (P < .001). On multiple regression analysis, the number of OPV doses was the only factor that showed a positive correlation with the NPAFP rate."