I remember an old episode of the Red Skelton Show, where Freddie the Freeloader found himself in the hospital and getting sicker. His diagnosis was that he was around too much clean.
“...theory about polio being mostly dormant until the 20th Century when most people were subject to cleaner, more sanitary conditions....”
Some truth to that but think about those weakened by age, infirmity etc were already victims of other diseases and just died before getting a chance of polio.
Just my opinion :-)