Anti-vaccers use science to show how vaccines can be harmful. The number one gripe an anti-vaccer has is the use of adjuvants. They cause the immune system to have an allergic reaction and then identify anything in the area of the infection as bad, then the immune system attacks that thing they identified. Sometimes is aluminum or mercury, and sometimes its the cells in that part of the body, that's when you get a cytokine storm and convulsions and wonder why your talkative child is suddenly silent and less active.