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Flu information from the Centers for Disease Control and Prevention

►2009 H1N1 Flu
►2009 H1N1 Flu in Humans
►Prevention & Treatment
►Contamination & Cleaning
►Exposures Not Thought to Spread 2009 H1N1 Flu

What are vaccines and how do they work?

Vaccines are given to protect you from infections by bacteria or viruses. In other words, vaccines give you immunity to diseases. Vaccines work by exposing you to a harmless form of bacteria or virus so that your body's immune system is ready to fight the real thing in the future.

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What is the flu?

Colorized electron micrograph image of H1N1 virus.
-- CDC

"Flu" is short for influenza. It's an infection from a virus and mostly affects the nose, throat, and lungs. You might hear people say they have the "flu" when they are a little sick with a cold or an upset stomach, but the real flu usually makes you a lot sicker.

Slightly different types, or strains, of flu virus appear every year. Because people mostly get sick from these viruses in the fall and winter seasons, they are called seasonal flu.

Sometimes, a new strain of flu virus shows up that's very different from seasonal flu, like the H1N1 virus (also called swine flu) that's around now.

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►View a graphic explaining antigenic shift.

Influenza is caused by three species of viruses called Influenzavirus A, Influenzavirus B, and Influenzavirus C. These viruses infect people, birds, and other mammals such as seals, horses, and pigs.

Type A flu viruses cause the most severe disease. They have been to blame each time flu has traveled worldwide and infected many people.

Flu viruses are always slowly changing, so the viruses causing this year's seasonal flu are not exactly the same as last year's. This constant, gradual change is called antigenic drift.

Sometimes, two or more different kinds of virus combine with each other to form a dramatically different virus. This type of sudden, big change is called antigenic shift.

The 2009 H1N1 virus is a result of antigenic shift.

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If I've already had vaccines, why do I need vaccines for H1N1 and seasonal flu?

You have probably been given a bunch of different vaccines--for measles, mumps, polio, and tetanus...to name a few. Each vaccine contains antigens--generally, weakened forms or small pieces of bacteria or viruses that cause certain diseases. Each vaccine protects you against just the diseases it contains antigens for. That's why you get so many different shots.

To your body, the different strains of flu virus that appear each season are like different diseases, so each year you need a new seasonal flu vaccine that contains antigens for the "new" disease. This year, people also need a vaccine that contains antigens for the 2009 H1N1 strain.

Kids under 10 will need two vaccinations for seasonal flu and two vaccinations for H1N1 flu because young immune systems need a little more exposure to the antigens to form protective amounts of antibody.

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What do cows and chickens have to do with it?

Jenner

We can thank cows for one of the first vaccines.

The British doctor Edward Jenner (1749-1823) protected people from a deadly disease called smallpox by injecting them with cowpox, a weaker but similar disease found in cows. He invented the word vaccine based on the Latin word vaccinus, which means "from cows." We can thank chickens for providing the eggs in which flu viruses are grown for use in today's flu vaccine.

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Pasteur

Edward Jenner's vaccine used a weakened form of cowpox found in nature. The French scientist Louis Pasteur (1822-1895) later developed artificially weakened forms of cholera, rabies, and anthrax that could be injected in people to prevent these diseases.

Pasteur called these weakened diseases vaccines to honor Jenner's discovery.

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What else can I do to prevent flu?

Flu is passed from person to person by the tiny droplets that come out of your mouth and nose when you sneeze or cough. A very important way to prevent the spread of flu is to cough or sneeze into a tissue or your sleeve.

Don't forget to also wash your hands frequently and keep your hands away from your eyes, nose, and mouth. Plus, you can support your immune system by getting plenty of fruits and vegetables, exercise, and sleep.

For more tips, see www.flu.gov.

Visit www.terrificscience.org/flu.html for a fun paper and pencil activity called "Vaccinate Me!" to go with this reading.

Developed by the Center for Chemistry Education at Miami University, Ohio, with funding by a Science Education Partnership Award (SEPA) grant from the National Center for Research Resources of the National Institutes of Health.

Visit http://www.terrificscience.org/healthrich/activities.html for free activities on hand hygiene and other timely health topics.