“Vaccines do not work as well if a large number of folks opt out of the system. Vaccines are not 100% effective in any one individual. It is the collective immunity of the population (known as herd immunity) that keeps a germ from reaching epidemic proportions. You may think that if everyone else’s kid is protected then your child doesn’t need to be. But . . . germs don’t think that way. They just look for a new person to infect. And the more people who opt out, the more vulnerable the entire population is (particularly its youngest members).”