What is the flu?
Influenza, commonly called the flu, is a respiratory illness caused by a specific kind of virus. Compared to most viruses that cause upper respiratory illnesses (e.g., the common cold), influenza viruses usually cause a more severe illness that is more likely to lead to serious medical complications, such as pneumonia.
What kinds of viruses cause influenza?
Influenza viruses are divided into three types: A, B and C. Types A and B are responsible for the outbreaks of respiratory illness that occur almost every year and often are associated with increased rates of hospitalization and death. Currently there are three different influenza strains in worldwide circulation: two type A viruses and one type B. (Type C differs because it usually causes either a very mild respiratory illness or no symptoms at all.) However, influenza viruses continually change over time (usually by mutation). This enables a virus to evade a person's immune system, making people susceptible to influenza infection throughout their lives.
Occasionally, type A viruses can change abruptly and a new subtype will suddenly emerge. When this occurs, large numbers of people--sometimes an entire population--have no antibody protection. This results in a worldwide epidemic, or pandemic. There have been three influenza pandemics this century. In 1918-19, the Spanish flu caused approximately 500,000 deaths in the United States and 20 million worldwide. The Asian flu resulted in 70,000 U.S. deaths in 1957-58, and the Hong Kong flu of 1968-69 claimed 34,000 lives in the United States. However, these are rare events.
When is influenza most common?
The influenza season, when the illness is most common, usually occurs during the colder months of the year: late fall, winter and early spring.
What are the symptoms of influenza?
Typical symptoms include fever--often with chills and headache, muscle aches and fatigue. Respiratory symptoms are a cough, sore throat, and a runny or stuffy nose. Although nausea, vomiting and diarrhea can sometimes accompany an influenza infection, especially in children, gastrointestinal symptoms are rarely prominent. The term "stomach flu" is incorrectly used sometimes to describe gastrointestinal illnesses caused by other microorganisms.
How many people are affected by influenza each season?
During most years, between 10 percent and 20 percent of the population are infected with influenza viruses. Children get influenza more often than healthy adults. Older adults and people of any age with chronic illnesses are more apt to suffer from serious medical complications from influenza. In an average year, approximately 36,000 Americans die from influenza and its complications and many more are hospitalized.
What can be done to prevent influenza?
The best prevention is vaccination against flu. Because influenza viruses change frequently and because protection from the vaccine decreases with time, people should get vaccinated every year. The amount of vaccine manufactured in the United States has increased substantially in recent years. During the 2003-2004 influenza season, there were 88 million doses of vaccine available. While most people get shots against influenza, there is a nasal spray vaccine product for healthy persons between the ages for five and 49.
There are several antiviral drugs available that are effective in preventing and treating influenza. These drugs are available by prescription and are prescribed specifically for type A or B infections. However, they must be taken before or within 48 hours of onset of illness.
Who should get an influenza shot?
Anyone who wants to reduce his or her risk of getting influenza should get an annual flu vaccination. Vaccination is particularly important, though, for certain people at risk of complications from influenza:
Are there any good reasons not to get a flu shot?
Persons who have a severe allergy to eggs or who have had a previous allergic reaction to influenza vaccine should not get a flu shot without consulting a physician.
Many people avoid getting vaccinated for the wrong reasons:
When is the best time to get a flu shot?
In the United States, influenza activity is typically very low until December; peak activity most often occurs between January and March. Influenza vaccine should be administered between September and mid-November. It takes about one to two weeks after vaccination for antibodies against influenza to develop and provide protection.
What else can be done to avoid getting the flu?
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