Vaccines are like traffic lights; they ensure the safety of the public, be in heavily crowded areas, like schools, or densely trafficked roads. Traffic lights only work when all people follow the rules. If a car runs a red light, the car runs the risk of killing innocent pedestrians who are complying with the prescribed rules. Vaccines, if not utilized by most people, are ineffective. Even though some parents are concerned over the safety of vaccines, children who go to public schools should not be granted exemptions because vaccines are necessary to prevent outbreaks, children who do not receive vaccines are at risk of disease, and medically compromised children rely on vaccines to prevent disease. Vaccines are able to prevent disease in a single child, but their usefulness to society lies in their ability to prevent outbreaks. Vaccines prevent disease through the concept of herd immunity. Herd immunity is the idea that a disease will have a harder time spreading if the majority of the population is unable to contract it (Martinez). For example, if more than 90 percent of people are vaccinated against measles, an outbreak is unlikely to happen even if a person in the community is infected (Oster). The American Medical Association has cited the ability of vaccines to prevent measles, mumps and other infectious diseases in their stance against vaccine exemptions (Phillips). The Centers for Disease Control and Prevention certifies the efficacy of vaccines, specifically