success brought widespread acceptance, and mass vaccination campaigns have greatly reduced the incidence of many diseases in numerous geographic regions. The Centers for Disease Control and Prevention lists vaccination as one of the ten great public health achievements of the 20th century in the U.S. Mechanism of function Vaccines are a way of artificially activating the immune system to protect against infectious disease. The activation occurs through priming the immune system with an immunogen. Stimulating immune responses with an infectious agent is known as immunization. Vaccination includes various ways of administering immunogens. Most vaccines are administered before a patient has contracted a disease to help increase future protection. However, some vaccines are administered after the patient already has contracted a disease. Vaccines given after exposure to smallpox are reported to offer some protection from disease or may reduce the severity of disease. The first rabies immunization was given by Louis Pasteur to a child after he was bitten by a rabid dog. Since its discovery, the rabies vaccine has been proven effective in preventing rabies in humans when administered several times over 14 days along with rabies immune globulin and wound care. Other examples include experimental AIDS, cancer and Alzheimer's disease vaccines. Such immunizations aim to trigger an immune response more rapidly and with less harm than natural infection. Most vaccines are given by injection as they are not absorbed reliably through the intestines. Live attenuated polio, rotavirus, some typhoid, and some cholera vaccines are given orally to produce immunity in the bowel. While vaccination provides a lasting effect, it usually takes several weeks to develop. This differs from passive immunity (the transfer of antibodies, such as in breastfeeding), which has immediate effect. A vaccine failure is when an organism contracts a disease in spite of being vaccinated against it. Primary vaccine failure occurs when an organism's immune system does not produce antibodies when first vaccinated. Vaccines can fail when several series are given and fail to produce an immune response. The term "vaccine failure" does not necessarily imply that the vaccine is defective. Most vaccine failures are simply from individual variations in immune response. Vaccination versus inoculation The term "inoculation" is often used interchangeably with "vaccination." However, while related, the terms are not synonymous. Vaccination is treatment of an individual with an attenuated (i.e. less virulent) pathogen or other immunogen, whereas inoculation, also called variolation in the context of