Starting in 1939, we sprayed DDT (an insecticide) all over the United States. It doesn't contain heavy metals itself, but later studies found that it has a synergistic effect in the body with heavy metals (like lead, aluminum, and mercury), making heavy metal exposure more toxic. The number of polio cases climbed drastically after 1939, peaking in 1952, and dropping off to near zero in the 1960s. This was because DDT was found to be an environmental toxin, and its usage dropped dramatically in the 60s until it was outright banned in 1972. Lead usage was also widespread in the United States in the early and mid 20th century, in gasoline (leaded gasoline gives off lead into the air when burned), lead paint, and lead pipe plumbing, until it was also found to be toxic and its use declined precipitously.

https://ourworldindata.org/grapher/prevalence-of-polio-rates-in-the-united-states

The part that the medical industry, pharmaceutical industry, farming industry, media, and government doesn't tell us, is that heavy metal toxicity has symptoms very similar to polio. For lead specifically, these similar symptoms include loss of appetite, nausea, vomiting, fatigue, stomachache, abdominal pain, constipation, headache, irritability, muscle weakness and pain, tingling sensation in limbs, difficulty breathing, and paralysis. Other heavy metals display similar symptoms in the body.

The use of DDT combined with heavy metal toxicity was being misdiagnosed as polio. To "cure" us of "polio", the medical industry was injecting us with vaccines that contained heavy metal adjuvants, the same heavy metals which were causing the "polio". There's several stories of polio cases climbing after the polio vaccines were administered, precisely because of the heavy metal toxicity derived from the vaccines themselves.