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Friday, September 12, 2014

How Vaccines Work?

To understand how vaccines work, it is helpful to first look at how the body fights infections. When germs, such as bacteria and viruses infect or invade the body, they multiply and damage body tissues causing illness, which can be fatal. To ward off these germs, the body has an army of cells called lymphocytes that it calls upon. The counter offensive that the lymphocytes mount to eliminate the invading organisms is called immune response. There are two types of lymphocytes, B cells and T cells. Certain T cells, called cytotoxic T cells, destroy germs that are inside cells, while B cells produce antibodies that bind to and help kill the germs that are in tissues outside the cells. The first time the body encounters a particular germ, it mounts what is called a primary immune response. This process takes a long time to evolve because it consists of several steps. As the germ multiplies upon entering the body, body cells called antigen presenting cells capture a few of the germs and show these germs or parts of the germs (called antigens) to certain T cells (helper T cells). The helper T cells that have been shown the antigens then react by producing substances that stimulate: some B cells to produce antibodies; some other T cells to develop into cytotoxic T cells; and, some B and T cells to transform into memory B and T cells, respectively. While the primary immune response is building up, the individual gets and remains sick. Only after enough antibodies and cytotoxic T cells have been produced, which can take several days to weeks, will the infection be eliminated. An unsuccessful primary immune response leads to death but a successful one leads to recovery and immunity to the germ.
A successful immune response leaves behind a host of memory B and T cells that can immediately react and mount a rapid (one to two days) and vigorous response (called secondary immune response) every time the same germ enters the body. Often, the germ gets eliminated without the person even noticing that he/she has been infected that is why the person is said to be immune to the infection.

Vaccines are designed to imitate an infection. This type of infection however, does not cause illness. It simply stimulates the body to undertake a primary immune response and produce memory B and T cells. Vaccines vary in their composition. Some contain relatively harmless substances (antigens) that consist of, or are similar to, whole or parts of live or dead microorganisms; while others (called toxoids) consist of bacterial toxins or poisons that have been modified to render them nontoxic. In general, live vaccines confer life-long immunity after just one vaccination, while dead microorganisms and toxoids require repeated vaccinations and booster doses to maintain life-long protection.
Vaccines definitely work in preventing many potentially fatal diseases, but are they safe? Like any medicine, vaccines are not 100 percent risk free, but scientific studies—the latest of which, published in the July, 2014 issue of the medical journal Pediatrics, reviewed 20,000 scientific titles and 67 papers on vaccine safety—consistently show that side effects from vaccines outside of soreness and redness at the injection site are extremely rare. The British study that linked autism to childhood vaccines that you have been told about has actually been retracted after it was exposed to be an elaborate fraud. But there is evidence that the meningococcal vaccine can lead anaphylaxis (severe allergic reaction) while other studies link MMR vaccine to seizures.
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