by Cynthia Wall

Created on: February 07, 2009

In order to understand how the flu shot works, it is first necessary to understand what the flu is and what it does once inside your body. The flu (short for influenza) is a virus that causes a respiratory illness in its host. While people refer to the stomach flu, which also is a virus-caused illness, it is not technically the flu.

A virus is a tiny particle (about one-millionth of an inch long). The flu virus has three parts: Nucleic acid which is its set of genetic instructions; Protein coat which protects the genetic material; and a Lipid membrane which surrounds the protein coat. Not all viruses are protected by a membrane but flu viruses are making them especially long-lived outside of the body.

While flu viruses are hardy creatures, they do not contain the enzymes necessary to carry out the chemical reactions for life. For that, they need you a warm, inviting host, the perfect chemistry lab bed and breakfast for their wicked deeds. Once a person has inhaled the flu virus, it goes to work by attaching itself to a host cell. Once inside the cell, the viral enzymes take over the necessary enzymes of the host cell and begin making copies of the virus. Then the multitude of new viruses break open the host cell. The new viruses start attacking other cells. The viruses spread into your bloodstream and your lungs. Because you lose cells lining your sinuses in the process, fluid flows into your nasal passages and gives you a runny nose. Viruses in the fluid dripping down your throat attack the cells lining your throat making it sore. Viruses in your bloodstream attack muscle cells making you ache all over. In short, you are SICK.

As your immune system responds to the viruses, it produces chemicals called pyrogens

which make your temperature rise. The fever slows down the rate of viral reproduction. All of your immune responses continue until the virus is eliminated from your body. Of course, if your immune system isn't totally healthy, you may develop a secondary bacterial infection along the way such as pneumonia. Then you are REALLY SICK.

Your body's immune system has a good memory. It remembers the DNA or RNA of the flu virus you just had and has antibodies ready to fight it should you become infected again. The problem is that there are so many flu viruses in the world. They constantly mutate and create new ones. So it is highly unlikely that the immune response you have ready to fight last year's flu will serve you well for what may be coming next year. Flu

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