Vaccines are substances that are injected into the body to stimulate the body’s natural immune system against disease. Typically made with dead or weakened (attenuated) forms of the virus or germ that causes the disease, vaccines work by inducing the body to produce antibodies that attack the disease-causing organism.

Most health professionals believe vaccinations are a key to preventing disease epidemics and that maintaining high immunization rates is an important public health goal. Currently most doctors in the United States recommend that all children be vaccinated against several formerly common diseases, including diphtheria, measles, rubella (German measles), meningitis, mumps, polio, tetanus, and whooping cough (pertussis). Many medical organizations also recommend periodical vaccinations for adults. State and federal programs exist that provide vaccinations at low or no cost to poor families. Most states require vaccination before children enter school, but provide...