Isn't the number of polio cases way, way down since the polio vaccine was introduced, to the point that it's almost eradicated now? How could that have happened if all it did were make infections less severe?
There are two types of polio vaccine. The one used where polio is circulating (oral vaccine) is a live virus and provides more protection against transmission but isn't super effective and (rarely) can cause paralysis. The inactivated vaccine (injection) mostly just protects against severe disease. Here's a paper that says the oral vaccine produces 70-80% protection against transmission and the inactivated vaccine produces 20-30% protection: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2486742/
