College of American Pathologists
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  Seasonal Influenza Information




Updated July 31, 2009

What causes “the flu”?
Influenza, commonly called “the flu,” is caused by an influenza virus, which infects the respiratory tract (nose, throat and lungs).

How is it different from a common cold?
Unlike the common cold, the flu may cause severe illness or life-threatening complications.

How common is influenza?
Every year in the United States, five to twenty percent of the population gets the flu, more than 200,000 people are hospitalized from flu complications, and 36,000 people die from flu.

What are the symptoms of Influenza?
SSymptoms of flu include fever, headache, extreme fatigue, dry cough, sore throat, runny or stuffy nose, and muscle aches. Children can have additional gastrointestinal symptoms, such as nausea, vomiting, and diarrhea, but these symptoms are uncommon in adults.

How does Influenza spread?
Flu spreads mainly through person-to-person contact in respiratory droplets from both coughs and sneezes. A person may also become infected by touching something with the virus on it and then touching his or her mouth or nose.

What can I do to prevent from getting influenza?
Washing hands regularly and thoroughly can help prevent flu. But the best way to prevent the flu is to get a flu vaccination each fall. Yet fewer than half of all Americans who most need a flu shot get one. There are two types of vaccines:

  • The “flu shot”–an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm. The flu shot is approved for use in people older than 6 months, including healthy people and people with chronic medical conditions.
  • The nasal-spray flu vaccine–a vaccine made with live, weakened flu viruses that do not cause the flu (sometimes called LAIV for “live attenuated influenza vaccine” or FluMist®). LAIV (FluMist®®) is approved for use in healthy* people 2-49 years of age who are not pregnant.
  • Each vaccine contains three influenza viruses—one A (H3N2) virus, one A (H1N1) virus, and one B virus. The viruses in the vaccine change each year based on international surveillance and scientists' estimations about which types and strains of viruses will circulate in a given year.

How effective is the “flu shot”?
Flu shots prevent the illness in 70 to 90 percent of those vaccinated.

Who should get vaccinated?
The College of American Pathologists agrees with the recommendation that priority “at risk” groups get vaccinated. Those most at risk include:

  • Children aged 6 months up to their 19th birthday
  • Pregnant women
  • People 50 years of age and older
  • People of any age with certain chronic medical conditions
  • People who live with or care for those at high risk for complications from flu, including Health care workers, Household contacts of persons at high risk for complications from the flu, Household contacts and out of home caregivers of children less than 6 months of age (these children are too young to be vaccinated).
  • People who live in nursing homes and other long-term care facilities

How do the vaccines work?
Both vaccines work in the same way—the vaccines cause antibodies to develop in the body, and these new antibodies provide protection against the influenza virus infection.

When is the best time to get vaccinated?
Yearly flu vaccination should begin in September or as soon as vaccine is available and continue throughout the influenza season, into December, January, and beyond. This is because the timing and duration of influenza seasons vary. While influenza outbreaks can happen as early as October, most of the time influenza activity peaks in January or later.

How much is a flu shot?
Prices for shots range from $15 to $20. Medicare and most health plans cover flu shots.

Where can I find out more information about influenza?
To find more information about flu prevention, visit the Centers for Disease Prevention and Controls’ website.