Vaccines protect the population. You choose not to get vaccinated, okay. Maybe you then contract it. You very well may infect those who have not yet been vaccinated but intend to or are unable to at present.
I dont really know how polio works but if its a disease that spreads from person to person and its really rare in the modern world what are the chances of someone contracting it because they dont get their shot? And I guess thats just a chance people will have to take.