The simplest way to show it was done by Penn&Teller. Usually their shows are 100% not-Kosher, so don’t watch it, you have to find the specific clip which is “kosher.”
They took cardboard people and set them up on two squares. They then put a glass wall, representing vaccines, in front of one square. After that, they took out balls, representing diseases, and rolled it towards the cardboard people. Even if one of the vaccinated kids got hit by some wild ball, it was one kid out of 100 cardboard kids. The same couldn’t be said for the cardboard kids without the glass wall.