Vaccination is the process of administering vaccines, substances designed to cause the body to produce antibodies and learn how to fight diseases before the disease attacks in full force. Vaccinations prompt the immune system to take action against an antigen. There are several different types of vaccines, some actively in use today, and some still in experimental stages. Additionally, the concept of vaccination has stirred up controversy and theories about possible negative side effects.
The idea of inoculation (transferring a disease to another person, animal or plant to build disease resistance) has been present since 1000 AD when the Chinese used inoculation for smallpox. Additionally, Africa and Turkey used inoculation before the concept spread into Europe and the Americas.  On May 14, 1796, Edward Jenner created the first vaccination after noticing that the milkmaid who handled a cow’s udders did not usually contract smallpox. By taking some fluid from a cowpox blister and applying it to the skin of an eight-year-old boy named James Phipps. After the boy developed only a small blister that quickly receded, Jenner performed the same procedure, this time using smallpox fluid. After Phipps showed no reaction to the disease, Jenner’s work was considered a success and doctors began using the same treatment all over Europe, reducing the number of new developing cases of smallpox. 
Significant Years in Vaccine History –
1880’s- Louis Pasteur develops a vaccine for rabies.
1955- Polio Vaccine introduced.
1980- Smallpox is declared to be eradicated from the world.
Development of Immunization
Before discussing how vaccines work, it is important to have a brief understanding of how the immune system works. The National Institute of Allergy and Infectious Diseases states that "The immune system is a network of cells, tissue, and organs that work together to protect the body from infection". An infection occurs when pathogens such as bacteria or viruses enter the body, attack the cells of the body, and multiply inside the body. The attacks of these pathogens lead to the illnesses that we experience. The immune system, as the body's defense against pathogens, has many ways to fight against bacteria and viruses. In addition to the oxygen carrying red blood cells, blood also contains white blood cells that fight infections as part of the immune system. There are three main types of white blood cells. Macrophages are cells that use phagocytosis to engulf and digest pathogens or dying cells, leaving behind pieces of the pathogen called an antigen. Immune system cells will identify antigens and stimulate other cells to fight the harmful objects. B-lymphocytes are defensive immune system cells that produce antibodies, proteins that attach to and attack antigens that are left by the macrophages. T-lymphocytes attack cells of the body that have been infected by the pathogen.
When the body initially detects a pathogen, it may require several days to produce the amount of cells necessary to fight the infection. Once the pathogen has been eradicated, many of the immune system cells die, but the body keeps a small amount of T-lymphocytes (called memory cells) that recognize the antigen, and stimulate the B-lymphocytes to produce the correct antibodies to destroy the harmful organisms. More information can be found on the immune system page.
Vaccines assist in developing an acquired immunity by simulating an infection. Vaccines typically do not cause illness, but they stimulate the body to produce T-lymphocytes and antibodies to attack foreign objects. Once the body has completely fought off the simulation infection, many of the cells that fought against the pathogen will die, but the body will keep the memory cells to remember how to fight the pathogen and what antibodies to produce. This will protect the body from future infections because when the body detects the virus or bacterium in the future, it will recall exactly how to fight the pathogen and destroy it quickly, rather than waiting to produce the correct antibodies first. Sometimes after a vaccination, the body will develop minor illness symptoms as it fights the simulation infection.
There are seven primary types of vaccines that are currently used. These different vaccines all use different methods to prompt the body to fight against a particular disease.
Live Attenuated Vaccines - Live attenuated vaccines utilize an altered version of a pathogen that inhibits its ability to cause infection. In these vaccinations, the living pathogen is altered in a laboratory to weaken the cell, but still keep it alive. The live attenuated vaccine emulates a natural infection better than the other types of vaccines, and therefore generates a better and longer lasting immune system response. These vaccinations can sometimes result in lifetime immunity from one or two doses.
The advantage of live attenuated vaccines is accompanied by some risk as well. While it is unlikely, it is possible for the weakened cells to revert to virulent form and infect the recipient. Additionally, those with weakened immune systems from chemotherapy, or diseases such as HIV cannot receive these vaccines, as their immune systems may be too weak to fight the treatment.
Live attenuated vaccines are easier to create for viruses than bacteria.
Inactivated Vaccines - Inactivated vaccines are vaccines in which the pathogen has been killed by chemicals, heat, or radiation. Because these vaccines consist of dead microbes, they do not require refrigeration, therefore making them easier to transport, and they are safer because the microbes cannot come back to life and revert to their infectious state. Inactivated vaccines stimulate a weaker immune system response than live attenuated vaccines, and therefore require extra doses or "booster shots" to continue the immunity.
Subunit Vaccines - Subunit vaccines are vaccines that consist only of the antigens that stimulate the immune system, rather than the entire pathogen. Since these vaccines use only the antigen, or part of the antigen, the chances of negative side effects is lower. Subunit vaccines can consist of up to twenty or more antigens, but once the best immune system stimulating antigen has been discovered, scientists can create the vaccines in two ways: growing the pathogen in a lab and then breaking it apart with chemicals and retrieving the antigens, and manufacturing the antigen molecules through recombinant DNA technology. Vaccines made through the second method are called recombinant subunit vaccines. An example of recombinant subunit vaccine is the hepatitis B vaccine, which is produced through genetically altered yeast.
Toxoid Vaccines - Toxoid vaccines help prepare the immune system for certain toxin secreting bacteria. Scientists have found that bacteria secreted toxins can be inactivated through exposure to a formaldehyde and sterilized water solution known as formalin, resulting in an inert form of the toxin known as a toxoid. Exposure to toxoids allows the immune system to learn how to fight the toxins. Toxoid vaccines have been used to treat diphtheria and tetanus.
Conjugate Vaccines - Conjugate vaccines are a specialized type of subunit vaccines designed to prepare the immune system against bacteria with an outer coating of polysaccharides. These vaccines link antigens or toxoids from a pathogen that the patient's body recognizes to the polysaccharide, allowing the body to learn how defend against bacteria with these coatings. The haemophilus influenza type B vaccine is an example of a conjugate vaccine.
DNA Vaccines - DNA vaccines are an experimental vaccine in which the pathogen's DNA that code for antigens are introduced to the body. Some of the body's cells will take in the DNA and begin creating the antigen molecules necessary to stimulate the immune system. These vaccines pose little harm because they do not involve the pathogen itself, but rather, a fragment of its DNA. Additionally, these vaccines are cheap and relatively easy to produce.
Recombinant Vector Vaccines - Similar to DNA vaccines, recombinant vector vaccines use the body's cells to produce antigens of other pathogens. In recombinant vector vaccines, attenuated viruses are genetically altered with DNA from other microbes. When they infect body cells, they cause the cell to produce antigens, therefore stimulating the immune system. These vaccines are also still in experimental stages.
Connection to Autism
People have been debating the theory that vaccines can lead to autism for years. The idea surfaced in February of 1998 when Andrew Wakefield, a British gastroenterologist, and several assistants published a paper discussing the relation of vaccination to autism in addition to the relation of MMR vaccine to intestinal inflammation that lead to the translocation of peptides in the blood and therefore, the brain as well, affecting the brain's development. Since then, Wakefield's work has been considered invalid, as he has been accused of using incorrect research methods in producing these theories. Regardless of this fact, people have continued to connect autism to vaccination, as signs of autism typically show up in the developing stages between eighteen months and three years.
Many official research agencies such as the Centers for Disease Control and Prevention state that there is no relation between autism and vaccination. They state that there are no studies that suggest a correlation between the two.
This video explains the basic principles behind vaccines and how they work.
- Avian influenza
- Hepatitis B
- Hepatitis C
- Human papillomavirus
- Infectious mononucleosis
- Swine influenza
- Yellow fever
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