Disease Prevention through Vaccination: The Science and the Controversy

Each one of us is constantly warding off the potential for infection or disease. After all, the world is filled with countless microbes, fortunately most of which are harmless and some even beneficial. But there are plenty of microbes that can hurt us (pathogens, from the Greek word for disease, "pathos"). Harmful bacteria, for example, may cause disease through infection of their host or by the release of powerful toxins. Viruses, inert by themselves, have the ability to invade the cells of other life forms. As those cells duplicate, so does the virus. While one's ability to ward off disease is usually strong, there are instances where the microbes overwhelm the body and produce illness. In an effort to protect against many infectious diseases, we rely on vaccines with the intent of conferring protection and immunity.

Vaccines have been a vehicle for disease prevention and eradication for hundreds of years. The development and widespread distribution of safe, effective, and affordable vaccines has done more for disease prevention over time than nearly any other medical or public health intervention. Of the 10 greatest public health achievements over time, certainly immunization against disease ranks at or near the top of the list.[2] Millions of lives have been saved because of the widespread use of vaccines to prevent or eradicate diseases such as measles, diphtheria, pertussis, tetanus, polio, and, of course, smallpox. The eradication of smallpox worldwide is undoubtedly one of the most spectacular public health initiatives of all time.

Vaccination not only protects an individual from disease, but also has the dual role of protecting the community at large from disease outbreaks.

For disease to spread, there must be a pool of susceptible people in whom the bacteria or virus can grow. Ironically, those who elect not to vaccinate themselves or their children are actually benefiting from those who are vaccinated. This concept is referred to as "herd immunity." When a disease spreads from one human to another, it requires both an infected person to spread it and a susceptible person to catch it. Herd immunity works by decreasing the number of susceptible individuals, even those who refuse to be vaccinated, and when this number drops low enough, the disease will disappear from the community because there are not enough people to continue the catch-and-infect cycle. The greater the proportion of vaccinated individuals, the more rapidly the disease will disappear. Once-common diseases such as pertussis, polio, smallpox, and measles have all but disappeared thanks to the large numbers of individuals who are vaccinated against these diseases. Periodically, however, there have been mini-outbreaks of disease for which there are vaccinations. For example, there are outbreaks of measles (a particularly contagious, potentially serious disease) in the United States as well as around the world, primarily as a result of a pool of unvaccinated children.
Those who are not vaccinated are at high risk of contracting this disease.[3]