The pesticide DDT used in the 1940s-50s to fight malaria, was also sprayed on children to prevent polio. It caused polio-like paralysis instead. The first polio vaccine's rollout was disastrous.

CDC: Why CDC is Working to End Polio Globally - https://www.cdc.gov/global-polio-vaccination/why/?CDC_AAref_Val=https://www.cdc.gov/polio/why-are-we-involved/

WHO: History of Vaccines - https://www.who.int/news-room/spotlight/history-of-vaccination/a-brief-history-of-vaccination

EPA: DDT - A Brief History and Status - https://www.epa.gov/ingredients-used-pesticide-products/ddt-brief-history-and-status

Daily Mail: Shocking 1940s video shows how US children were sprayed with dangerous pesticide as neighbourhoods were gassed with the 'miracle cure' that could kill mosquitoes and end Polio - https://www.dailymail.co.uk/news/article-5467597/Children-sprayed-dangerous-pesticide-DDT-shocking-clip.html

CDC: DDT - https://www.cdc.gov/niosh/idlh/50293.html

Washington Post: The tainted polio vaccine that sickened and fatally paralyzed children in 1955 - https://img.washingtonpost.com/history/2020/04/14/cutter-polio-vaccine-paralyzed-children-coronavirus/