evidence: Most vaccines contain either a dead or weakened germ (or parts of it) that causes a particular disease. Some help the body to make a protein that looks like it came from a germ. [...] It is true that a single child's chance of catching a disease is low if everyone else is fully vaccinated. But your child is also exposed to people other than those at school. And if one person thinks about skipping vaccines, chances are that others are thinking the same thing. Each child who isn't vaccinated gives highly contagious diseases another chance to spread. [...] Vaccines are intended to help keep healthy kids healthy. Because vaccines work by protecting the body before disease strikes, if you wait until your child gets sick, it will be too late for the vaccine to work. The best time to vaccinate kids is when they're healthy.