Polio vaccines are not only ineffective in preventing paralysis, they carry the risk of contamination with many harmful adventitious microorganisms, of which only some monkey viruses have been researched in more detail. Many other potentially dangerous microorganisms remain unaddressed.
https://web.archive.org/web/20201207083415/https://www.bmj.com/content/344/bmj.e2398/rr/599724