A vaccine is a biological preparation that provides immunity to a specific disease. It usually contains a weakened or inactive form of the disease which then stimulates the body's immune system to recognize it as a threat and destroy it, giving it the means to destroy any further versions of it that it may encounter in the future.
Vaccines have been proven to be the most effective method of preventing and eradicating infectious diseases. The complete eradication of smallpox and significant reduction of polio, measles, and tetanus have proven as such.
Vaccines lead to a phenomenon known as "herd immunity" in which diseases cannot spread with ease as the majority of a population are vaccinated. However, herd immunity can only work if a certain percentage of the population is vaccinated.
Most vaccines are delivered via injection, although notable exceptions include the polio vaccine which is often delivered orally. This method was found to have certain advantages as it allowed for administration by staff without formal training, and reduced the risk of blood contamination.
