Vaccination

Active immunization is the protection of susceptible humans and domestic animals from communicable diseases by the administration of vaccines (Vaccination). A vaccine is a preparation from an infectious agent that is administered to humans and other animals to induce protective immunity. It may consist of preparation of killed microorganisms; living, weakened (attenuated) microorganisms; inactivated bacterial toxins (toxoids); purified macromolecules; recombinant vectors or DNA vaccines.

The modern era of vaccines and vaccination began in 1798 with Edward Jenner�s use of cowpox as a vaccine against smallpox and in 1881 Louis Pasteur�s Anthrx vaccine. Vaccines were eventually developed against most of the epidemic diseases that had plagued Western Europe and North America. Indeed toward the end of the 20th century it began to seem that the combination of vaccines and antibiotics would temper the problem of microbial infections. Such optimism was cut short by the emergence of a new or previously unrecognized diseases and antibiotic resistance to old ones. Nevertheless, vaccination is still one of most cost effective weapons for microbial disease protection.

Vaccination of most children should begin at about 2 months of age. Before that age they are protected by passive natural immunity. Vaccination of adults depends on their risk group. For individuals living in closed quarters (military personnel), the elderly, and those individuals with reduced immunity (transplant patients, people with sickle cell anemia), vaccines for influenza, meningitis, and pneumonia are given. Depending on the country of travel, international travelers are routinely immunized against cholera, hepatitis, plague, polio, typhoid, typhus and yellow fever.

Passive immunization artificially acquired passive immunity can be produced by injecting an animal or human with preformed antibodies that have been produced in another animal, in another human, or in vitro. This type of immunization is called passive because protection does not require participation of recipient�s immune system. Passive immunization is routinely administered to individuals exposed to certain microbial pathogens that cause diseases such as botulism, diphtheria, hepatitis, measles, rabies and tetanus as well as to protect them against snake and spider bites. However, this type of immunization should be used only when necessary because of the risk involved such as developing anaphylaxis, serum sickness or type III hypersensitivity reaction. Furthermore, the protection lasts only as long as the antibody molecules survive in the recipient months with antibodies from another human, but only weeks with antibodies from animals or in vitro methods.

Types of Vaccines

Whole organism vaccines Many of the current vaccine in use for human that are effective against viral or bacterial diseases consists of whole organisms that are either inactivated (killed) or attenuated (live but avirulent).