In order to go about attenuating his polio vaccine, he repeatedly passed the virus through monkeys. Using methods of production that were later described as "hair-raisingly amateurish, the therapeutic equivalent of bath-tub gin," Kolmer ground the spinal cords of his infected monkeys and soaked them in a salt solution. He then filtered the solution through mesh, treated it with ricinolate, and refrigerated the product for 14 days to ultimately create what would later be prominently critiqued as a "veritable witches brew".In keeping with the norms of the time, Kolmer completed a relatively small animal trial with 42 monkeys before proceeding to self experimentation in 1934. He tested his vaccine upon himself, his two children, and his assistant. He gave his vaccine to just 23 more children before declaring it safe and sending it out to doctors and health departments for a larger test of efficacy. By April 1935, he was able to report having tested the vaccine on 100 children without ill effect. Kolmers first formal presentation of results would not come about until November 1935 where he presented the results of 446 children and adults he had vaccinated with his attenuated vaccine. He also reported that together the Research Institute of Cutaneous Medicine and the Merrell Company of Cincinnati (the manufacturer who held the patent for his ricinoleating process) had distributed 12,000 doses of vaccine to some 700 physicians across the United States and Canada.
The fact that the CIA organized a fake vaccination program in 2011 to help find Osama Bin Laden is an additional cause of distrust. In 2015, the WHO announced a deal with the Taliban to encourage them to distribute the vaccine in areas they control. However, the Pakistani Taliban was not supportive. On 11 September 2016, two unidentified gunmen associated with the Pakistani Taliban, Jamaat-ul-Ahrar, shot Zakaullah Khan, a doctor who was administering polio vaccines in Pakistan. The leader of the Jamaat-ul-Ahrar claimed responsibility for the shooting and stated that the group would continue this type of attack. Such resistance to and scepticism of vaccinations has consequently slowed down the polio eradication process within the two remaining endemic countries. Travel requirements
Travellers who wish to enter or leave certain countries must be vaccinated against polio, usually at most 12 months and at least 4 weeks before crossing the border, and be able to present a vaccination record/certificate at the border checks. : 25–27  Most requirements apply only to travel to or from so-called polio-endemic, polio-affected, polio-exporting, polio-transmission, or high-risk countries. As of August 2020, Afghanistan and Pakistan are the only polio-endemic countries in the world (where wild polio has not yet been eradicated). Several countries have additional precautionary polio vaccination travel requirements, for example to and from key at-risk countries, which as of December 2020 include China, Indonesia, Mozambique, Myanmar, and Papua New Guinea.