If a whole population is immunised against a pathogen we achieve ‘herd immunity’ and lower the risk of anyone getting the disease dramatically.
Vaccination is a form of active artificial immunity that involves exposing a patient to an antigen to stimulate an adaptive immune response. This means that if the patient is exposed to the antigen in future, the immune system will be able to mount a more efficient response. Antigens are usually proteins found on the surface of pathogens such as bacteria or viruses. Sometimes an attenuated or less virulent version of the whole pathogen may be injected. Widespread vaccination has resulted in the eradication of diseases such as smallpox, and is restricting diseases such as polio and measles.
Jonas Salk, the scientist who developed the vaccination for Polio, gave the formula away for free. It is now evaluated to be worth $7 Billion.