W
hat is Biology Good For?
Keeping Us Healthy During Flu Season: Flu Vaccines

(This assignment is optional. Read this essay and answer the questions at the bottom for 3 extra credit points. You may only turn in one per six weeks. The assignment is due one week before the end of the six weeks. It is not necessary to visit the links in the text unless you are interested in more information.)


Every year, the influenza virus causes the death of about 20,000 Americans and over 1 million people worldwide! People get the flu when the virus enters their body on a water droplet (perhaps from someone nearby sneezing) and invades their cells. A healthy immune system can kill the virus, but the whole process takes about a week. However, the virus replicates so rapidly that a person (especially with a weakened or developing immune system) may die or suffer complications such as pneumonia from the virus before the body can inactivate it. [Image: Los Alamos National Labs]

One way to prevent the flu is by getting a flu shot, or vaccine. Vaccination provides a 'training exercise' for the immune system. The weakened virus injected during a flu shot is carried to the lymph nodes, where the immune system kicks in. B-cells (with some assistance from Helper T-cells) turn on genes to produce antibodies to the virus. These antibodies coat the flu virus and signal it to be digested by macrophage cells in the immune system. If a person then inhales a live virus, the body is already prepared with antibodies to fight off that virus.

The flu vaccine is 70 - 90% effective in preventing the flu, but is good for that year only. The influenza virus mutates (changes) its DNA rapidly, and each year, many new strains of influenza develop. Two main proteins, hemagglutnin and neuraminidase, are changed every year as a result of these genetic mutations. That is why a new flu vaccine must be prepared every year, and why people get a flu shot every year.

In the U.S., new vaccines start to be mixed every fall for distribution in October and November. The new flu vaccine made every year includes the virus strains that are most common during that particular flu season. The Centers for Disease Control in Atlanta, GA has determined that the 2002-2003 flu vaccine would consist of proteins of three influenza strains: the A/Moscow, A/New Caledonia, and B/Hong Kong-like viruses. A new strain of flu virus (known as H1N2) is already causing the flu this in other parts of the world this January, like India, Egypt, and England, but fortunately, this year's vaccine should provide protection against the new H1N2 strain.

How different is this year’s flu shot from the ones of the last few years? As a comparison, the 2001-2002 flu shots contained the 3 influenza strains A/Moscow, A/New Caledonia, and B/Sichuan, and the 2000-2001 flu shot contained the 3 flu strains A/Panama, A/New Caladonia, and B/Yamanashi. Each flu season usually includes a combination of 'old' and 'new' viral strains.

How is the Flu Vaccine made? The influenza strains chosen are sent to pharmaceutical companies, and injected into millions of chicken eggs, where the viruses replicate in the egg albumin (egg white). Virus particles isolated from the egg white are then purified, inactivated, and dispensed into vials. According to the Centers for Disease Control , in October and November 2002, Aventis-Pasteur and other companies together produced 93 million doses of the flu vaccine in the Fall of 2002 - a record number!- at a cost of $2 - $3 per vaccine. [Image of antibodies]

How do you know whether you have a cold, caused by a bacteria, or the flu, caused by an influenza virus? Grab a box of Kleenex and see the comparison chart here!

Alternatives to a flu shot – a flu nasal spray?: Medimmune (formerly Aviron), a biotechnology company in Mountain View, CA, has just completed clinical trials on a flu vaccine, FluMist, that is delivered as a nasal spray. Once it receives clearance from the Food and Drug Administration , this nasal spray should be available, possibly for the 2003-2004 flu season. In clinical trials, FluMist provided up to 93% protection against influenza virus.

What if you already have the flu? Tamiflu, developed by Hoffman-LaRoche, lessens flu symptoms in adults and may even prevent a person from getting the flu.

Information, images, and quotes from this Good For, and more information on this topic can be found in the February 2001 issue of Scientific American, p. 82-83

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Extra Credit Questions: Please answer the following questions on a piece of paper and turn it into me.


1. List 2 famous flu epidemics, and the approximate number of deaths from each. (See the section "Natural History of Human Influenza").
2. Why do you think a nasal spray would be a good way to deliver a flu vaccine?
3. How does
Tamiflu work ? (ie: what are you taking when you take this medicine?)

 

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