It was not polio , it was DDT poison.
If you Google “DDT trucks,” you will find a lot of different pictures like this..
they sprayed playgrounds & orchards with DDT (with children still playing in the clouds of pesticides!) that is why kids got paralyzed! Or from the shots themselves! https://m.facebook.com/EatCleanTrainMeanLiveGreen/photos/a.207653335966694.52586.201613513237343/730387500359939/?type=3
DDT was considered and promoted as safe.. but it had a dark side.