vaccination

vaccination, means of producing immunity against pathogens, such as viruses and bacteria, by the introduction of an killed or weakened microorganism, a harmless piece of a microorganism, or the like to stimulate the body to produce antibodies against more dangerous forms. Vaccination was used in ancient times in China, India, and Persia, and was introduced in the West in 1796 by Edward Jenner. Jenner demonstrated that rubbing or scraping the cowpox virus (the term vaccine comes from the Latin vacca, cow) into the skin produced only a local lesion but was sufficient to stimulate the production of antibodies that would defend the body against the more virulent smallpox. Modern vaccines may use an inactivated or killed microbe; a weakened or altered (attenuated) live microbe; an inactivated toxin (toxoid); a harmless component (subunit) of a microbe, such as a protein or sugar, which may be combined with a substance (adjuvant) or protein that provokes a stronger immune response, or a gene inserted into another virus or cell to produce a protein; or messenger RNA (mRNA), which provides the instructions for producing a protein.

Vaccination has eradicated smallpox worldwide and prevents such diseases as cholera, rabies, and typhoid fever. Vaccines work with the immune system's ability to recognize and destroy foreign proteins (antigens) that it determines are “nonself.” Scientists are using this same principle to help the body recognize antigens peculiar to cancer cells. It is also applied in an experimental04/96 birth control vaccine that tricks the immune system into believing that human chorionic gonadotropin (HCG), a hormone secreted by a developing fertilized egg, is foreign, thus inactivating it and inducing menstruation even if fertilization has occurred. Vaccines are also used to control animal pests by conferring temporary infertility.

Vaccination programs have been notably successful in the United States. For example, in 1998 the Centers for Disease Control and Prevention reported only one case of poliomyelitis, one of diphtheria, 34 of tetanus, and 89 of measles. Despite the availability of vaccines, many thousands of people in the United States still die each year from vaccine-preventable diseases such as hepatitis and influenza.

Immunization against 17 diseases is recommended for young children and adolescents: hepatitis B (HepB); rotavirus; diphtheria, tetanus (lockjaw), and pertussis (whooping cough), given together as DTaP (formerly DTP) and, for older children, Tdap; Haemophilus influenzae b (Hib); poliomyelitis (IPV); pneumococcal infections, including pneumonia, meningitis, and bacteremia (PCV and PPV); measles, mumps, and rubella, given together as MMR; chickenpox (Var); hepatitis A (HepA); influenza; Neisseria meningitidis (meningococcal meningitis; MCV4, MPSV4); and human papillomavirus (HPV). Vaccination for shingles (herpes zoster) is recommended for persons aged 50 yearsor older, and annual vaccination for influenza is recommended for everyone six months or older. Researchers are working to develop combination vaccines that would simplify vaccine administration. Immunization against diseases such as yellow fever may be necessary before traveling to some countries. In 2002 the U.S. government decided to reinstitute smallpox vaccination for many military, health-care, and emergency personnel because of concern about a possible bioterror attack using smallpox.