While I feel for your friend, polio hasn't been given for a generation and a half in the US, so isn't really an apropos topic of discussion. (And is one of the last oral vaccines, which usually use attenuated viruses instead of dead ones).

Any time you stick a needle into someone, you risk giving them a brain embolism. Life is risk. However vaccines are CLEARLY in the make you much safer part of risk, like seatbelts and washing your hands.