Vaccination



Vaccines take advantage of your body’s natural ability to learn how to eliminate almost any disease-causing germ, or microbe, that attacks it. Traditional vaccines contain either parts of microbes or whole microbes that have been killed or weakened so that they don’t cause disease. When your immune system confronts these harmless versions of the germs, it quickly clears them from your body. In other words, vaccines fix the fight but at the same time teach your body important lessons about how to defeat its opponents.

Vaccine Benefits

Vaccines, which provide artificially acquired immunity, are an easier and less risky way to become immune. Vaccines are one of the few medicines that prevent a disease from occurring in the first place, rather than attempting a cure after the fact. It is much cheaper to prevent a disease than to treat it. According to one analysis, every dollar spent on vaccinating children against rubella, or German measles, in the United States saves nearly $8 in costs associated with treating the disease.

Vaccines protect not only you but everyone around you. If your vaccine-primed immune system nips an illness in the bud, you will be contagious for a much shorter period of time, or perhaps not at all. Similarly, when other people are vaccinated, they are less likely to give the disease to you. So vaccines protect not only individuals, but entire communities. That is why vaccines are key to the public health goal of preventing diseases. If a critical number of people within a community are vaccinated against a particular illness, the entire group becomes less likely to get the disease. This protection is called herd immunity, or community immunity.

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Harmful Microbes

Vaccines protect against infectious diseases caused by microbes-organisms too small to see without a microscope. Many microbes, such as bacteria, are made up of only one cell. Viruses, mere snippets of genetic material packed inside a membrane or a protein shell, are even smaller.

Here are a few list of some of the most serious disease-causing microbes for which vaccines exist. Page Top

How Vaccines Work All cells and microbes wear a “uniform” made up of molecules that cover their surfaces. Each of your cells displays marker molecules unique to you. The yellow fever viruses display different marker molecules unique to them. By “feeling” for these markers, the macrophages and other cells of your immune system can distinguish among the cells that are part of your body, harmless bacteria that reside in your body, and harmful invading microbes that need to be destroyed.

The molecules on a microbe that identify it as foreign and stimulate the immune system to attack it are called antigens. Every microbe carries its own unique set of antigens. As we will see, these molecules are central to creating vaccines.

Antigens Sound the Alarm

The macrophages digest most parts of the yellow fever viruses but save the antigens and carry them back to the immune system’s base camps, also known as lymph nodes. Lymph nodes, bean-sized organs scattered throughout your body, are where immune system cells congregate. In these nodes, macrophages sound the alarm by “regurgitating” the antigens, displaying them on their surfaces so other cells can recognize them. In particular, the macrophages show the yellow fever antigens to specialized defensive white blood cells called lymphocytes, spurring them to swing into action. By this time, about 3 days after the mosquito bite, you are feeling feverish and have a headache. You decide to stay home from work. Lymphocytes: T Cells and B Cells There are two major kinds of lymphocytes, T cells and B cells, and they do their own jobs in fighting off your yellow fever. T and B cells head up the two main divisions of the immune system army.

Antibodies in Action

The antibodies secreted by B cells circulate throughout your body until they run into the yellow fever virus. Antibodies attack the viruses that have not yet infected a cell but are lurking in the blood or the spaces between cells. When antibodies gather on the surface of a microbe, it is bad news for the microbe. The microbe becomes generally bogged down, gummed up, and unable to function. Antibodies also signal macrophages and other defensive cells to come eat the microbe. Antibodies also work with other defensive molecules that circulate in the blood, called complement proteins, to destroy microbes.

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Clearing the Infection: Memory Cells and Natural Immunity

Your immune system gains the upper hand. Your T cells and antibodies begin to eliminate the virus faster than it can reproduce. Gradually, the virus disappears from your body, and you feel better. You get out of bed. Eventually, you go back to working the docks.

Memory cells. After your body eliminated the disease, some of your yellow-fever-fighting B cells and T cells converted into memory cells. These cells will circulate through your body for the rest of your life, ever watchful for a return of their enemy. Memory B cells can quickly divide into plasma cells and make more yellow fever antibody if needed. Memory T cells can divide and grow into a yellow-fever-fighting army. If that virus shows up in your body again, your immune system will act swiftly to stop the infection

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Different Types of Vaccines

Live, Attenuated Vaccines

Some scientists might explore the possibility of a live, attenuated vaccine against X. These vaccines contain a version of the living microbe that has been weakened in the lab so it can’t cause disease. This weakening of the organism is called attenuation. Because a live, attenuated vaccine is the closest thing to an actual infection, these vaccines are good “teachers” of the immune system: They elicit strong cellular and antibody responses, and often confer lifelong immunity with only one or two doses.

Live, attenuated vaccines are relatively easy to create for viruses. Viruses are simple microbes containing a small number of genes, and scientists can therefore more readily control their characteristics. Viruses often are attenuated by growing generations of them in specific types of cells that make it hard for the virus to reproduce. This hostile environment takes the fight out of viruses: As they evolve to adapt to their new environment, they become weaker with respect to their natural host, human beings.

Inactivated or “Killed” Vaccines

An inactivated vaccine might be better for bacterium X. Scientists produce inactivated vaccines by killing the disease-causing microbe with chemicals, heat, or radiation. Such vaccines are more stable and safer than live vaccines: The dead microbes can’t mutate back to their disease-causing state. Inactivated vaccines usually don’t require refrigeration, and they can be easily stored and transported in a freeze-dried form, which makes them accessible to people in developing countries.

Subunit Vaccines

Scientists would certainly look into the possibility of a subunit vaccine for X. Subunit vaccines dispense with the entire microbe and use just the important parts of it: the antigens that best stimulate the immune system. In some cases, these vaccines use epitopes-the very specific parts of the antigen that antibodies or T cells recognize and bind to. Because subunit vaccines contain only the essential antigens and not all the other molecules that make up the microbe, the chances of adverse reactions to the vaccine are lower.

Subunit vaccines can contain anywhere from 1 to 20 or more antigens. Of course, identifying which antigens from bacterium X best stimulate the immune system would be a tricky, time-consuming process. Once scientists did that, however, they could make subunit vaccines against X in one of two ways. They could grow bacterium X in cultures, then use chemicals to break it apart and gather the important antigens.

Toxoid Vaccines

Because our imaginary bacterium X secretes a toxin, or harmful chemical, a toxoid vaccine might work against it. These vaccines are used when a bacterial toxin is the main cause of illness. Scientists have found they can inactivate toxins by treating them with formalin, a solution of formaldehyde and sterilized water. Such “detoxified” toxins, called toxoids, are safe for use in vaccines. When the immune system receives a vaccine containing a harmless toxoid, it learns how to fight off the natural toxin. The immune system produces antibodies that lock on to and block the toxin.

Conjugate Vaccines

If bacterium X possessed an outer coating of sugar molecules called polysaccharides, as many harmful bacteria do, researchers would try making a conjugate vaccine for X. Polysaccharide coatings disguise a bacterium’s antigens so that the immature immune systems of infants and younger children can’t recognize or respond to them. Conjugate vaccines, a special type of subunit vaccine, get around this problem. When making a conjugate vaccine, scientists link antigens or toxoids from a microbe that an infant’s immune system can recognize to the polysaccharides. The linkage helps the immature immune system react to polysaccharide coatings and defend against the disease-causing bacterium.

DNA Vaccines

Once the genes from bacterium X had been analyzed, scientists could attempt to create a DNA vaccine against it. Still in the experimental stages, these vaccines show great promise, and several types are being tested in humans. DNA vaccines take immunization to a new technological level. These vaccines dispense with both the whole organism and its parts and get right down to the essentials: the microbe’s genetic material. In particular, DNA vaccines use the genes that code for those all-important antigens.

Recombinant Vector Vaccines

Recombinant vector vaccines could be another possible strategy against bacterium X. These experimental vaccines are similar to DNA vaccines, but they use an attenuated virus or bacterium to introduce microbial DNA to cells of the body. “Vector” refers to the virus or bacterium used as the carrier.

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Vaccines of the Future

One day, vaccines may be eaten at the dinner table, applied via a skin patch, or squirted up your nose rather than administered as a shot in the arm-or elsewhere.

Making Safe Vaccines

No vaccine is perfectly safe or effective. Each person’s immune system works differently, so occasionally a person will not respond to a vaccine. Very rarely, a person may have a serious adverse reaction to a vaccine, such as an allergic reaction that causes hives or difficulty breathing. But serious reactions are reported so infrequently-on the order of 1 in 100,000 vaccinations-that they can be difficult to detect and confirm. More commonly, people will experience temporary side effects such as fever, soreness, or redness at the injection site. These side effects are, of course, much preferable to coming down with the illness.

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Information obtained from National Institute of Health
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