Controlling the spread of disease is one of the important aspects of epidemiology. There are many ways to decrease the risk of infectious disease spread. Handwashing, coughing into a tissue or one's shoulder, and cleaning and protecting cuts are some of the everyday ways people can decrease their risk of spreading infection.
Vaccinations, the use of a vaccine to stimulate antibody production and confer immunity, are a highly effective way to control disease spread. Obtaining a vaccine for contagious diseases, or those diseases spread from one organism to another through direct or indirect contact, will often result in full immunity to that disease for the individual. An example of such a vaccine is that for smallpox, which was caused by two viral variants, Variola Major and Minor. Smallpox used to be a contagious disease but because of a worldwide vaccination initiative, the last documented case was diagnosed in 1977. In 1980, the World Health Organization declared global eradication of the disease.Measles is a contagious disease caused by the rubeola virus. For every person infected with measles, the disease can spread to another 10 to 15 people. Vaccinations for measles can reduce the incidence of the disease, the number of new cases recorded during a certain period of time. If 90 to 95% of the population is to be vaccinated for the rubeola virus, the population can achieve herd immunity. Herd immunity refers to a situation in which a sufficient number of individuals in a population are immune to a contagious disease so that the disease spread is severely limited. This occurs when individuals vaccinated against a particular disease are not only immune themselves but they also cannot spread the disease to other people who may be susceptible to severe infection. The question of how many people need to be vaccinated in order for herd immunity to take effect depends on the particular pathogen and how contagious it is. Poliomyelitis, caused by the poliovirus, is less contagious than measles. Comparatively, 80 to 85% of the population needs vaccination in order for herd immunity to take place. Herd immunity is critical to protect individuals that may be too young to be vaccinated or suffer from a medical condition that makes them unable to get vaccinated. Unfortunately, herd immunity does not work for all diseases—only for those that are contagious, or spread from person to person. For example, Clostridium tetani, the causative agent of tetanus, lives in the soil. People contract tetanus if they have an open wound on their foot and walk barefoot in soil containing C. tetani. Even if individuals in the community get vaccinated against C. tetani, that will not prevent unvaccinated individuals from contracting tetanus from contaminated soil.
Depending on the patient's condition and infectious agent, the best option may be isolation and/or quarantine. When a patient is feeling ill, isolation is one of the best ways to prevent spreading that illness to others. Some diseases are so highly contagious that it is dangerous to leave patients around other people. This leads to quarantine procedures, which are meant to protect the patient and the health care workers.