Some diseases can be prevented by immunizations. Immunizations try to make a person have an immune reaction to an infectious agent. This is usually done before the person gets the disease. Examples of diseases prevented by immunizations are: polio, tetanus, and pertussis. In some cases, if all of the disease can be removed from society, we can get rid of the disease completely. An example of this is smallpox. This virus used to kill people, cause blindness, and bad scars. Now there has not been a person who had smallpox in over thirty years.