Polio was in worldwide decline since the early 1900s with occasion outbreaks....If what I say is true, why?
Because there is only 1 way to get polio, as nasty as it sounds. It comes from feces. The live virus is shed through the intestinal tract, and passes out in feces. This is the way it spreads.
Now, think about what occurred at the beginning of the 20th century in terms of sanitation. Flush Toilets, Sanitary sewers, etc. The potential for exposure dropped.
https://www.history.com/news/8-things-you-may-not-know-about-jonas-salk-and-the-polio-vaccine
https://www.sciencehistory.org/historical-profile/jonas-salk-and-albert-bruce-sabin
The idea that a virus that causes neurological damage (paralysis) could have a side-effect on neurological function should not be dismissed as Hoax, UNTIL and UNLESS proper research (double blind) has been conducted.
Nobody has conducted it, so this is why the controversy continues....
It is also contagious——very important.
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