I don't remember the specific time frames but I remember reading that DDT poisoning symptoms are extremely similar to polio symptoms. They thought the DDT was killing the polio virus. When more people were getting polio symptoms (from the DDT), they kept spraying more DDT (making the problem worse.

I also remember reading that polio was already on the decline before the vaccine, and continued to decline after the vaccine, and the same trend happened in Europe (who did not have a polio vaccine).

There's also this: more polio cases caused by mutant strains from vaccination than from polio in the wild.

https://www.npr.org/sections/goatsandsoda/2017/06/28/534403083/mutant-strains-of-polio-vaccine-now-cause-more-paralysis-than-wild-polio

https://nationalpost.com/health/more-polio-cases-currently-caused-by-vaccines-than-the-wild-virus-who-report