What is influenza?

Influenza is commonly referred to as “the flu.” It is a contagious respiratory illness caused by influenza viruses that affect the nose, throat, and lungs. There are two main types of influenza virus: A and B. Each type includes many different strains that tend to change from year to year.

When does influenza occur?

In the United States, influenza occurs most often in the late fall and winter months.

Who gets influenza?

Anyone can get influenza, but it is more likely to cause serious illness in young children, pregnant women, older persons, people with chronic illnesses (e.g., lung disease, heart disease, cancer, or diabetes) or those with weakened immune systems.

How is influenza spread?

Influenza spreads mainly by droplets from the nose or throat that are released when an infected person coughs or sneezes. Influenza can spread from one person to another beginning about one day before symptoms start through about a week after onset.

What are the symptoms of influenza?

Influenza symptoms can include a sudden onset of fever, headache, chills, cough, sore throat, and body aches. In children, vomiting and diarrhea might occur. Although most people are ill for less than a week, some people have complications and may need to be hospitalized.

How soon after exposure do symptoms appear?

Symptoms usually appear one to three days after exposure.

How is influenza diagnosed?

Doctors usually diagnose influenza based on symptoms and may use laboratory tests for influenza.

What is the treatment for influenza?

Rest, liquids, and over-the-counter medicines for fever and discomfort are the usual treatments. Prescription antiviral drugs are available and may reduce the severity of influenza. Aspirin should not be given to children with fever-causing illnesses because of the possibility of a complication called Reye’s syndrome.

How can influenza be prevented?

You can take three important steps to fight the flu:

  • Get vaccinated.
  • Stop the spread of flu and other germs by covering your mouth and nose with a tissue when coughing or sneezing; washing your hands often to help protect yourself from germs; avoiding touching your eyes, nose or mouth; staying home from work, school, and other activities when you are sick; and avoiding close contact with people who are sick.
  • Use antiviral drugs if your doctor recommends them.

Who should be vaccinated against influenza?

All persons aged six months or older should be vaccinated against influenza each year. Particular effort should be made to immunize people at higher risk for influenza infection or complications, including:

  • Pregnant and postpartum women, or those who will be pregnant during the influenza season
  • Persons over 65 years of age, including residents of nursing homes and long-term care facilities
  • People who have chronic lung or heart problems, including asthma
  • People who have other serious medical conditions, such as diabetes, kidney disease, cystic fibrosis, anemia, cancer, weak immune systems (including those with HIV), or a seizure disorder

To help prevent the spread of influenza to people in high-risk groups, those who live with people in a high-risk group and healthcare workers who provide care to high-risk patients should also receive an annual influenza vaccine. Travelers to countries outside of the U.S. may also need to consider influenza vaccination.

If I was vaccinated last year do I need a new flu vaccine this year?

Yes. It is important to receive a new flu vaccine every year. The formula for the vaccine can change from year to year, based on what strains of influenza virus are circulating. Also, protection offered by the influenza vaccine typically only lasts for several months. It is important that you receive a new vaccine every year.

Should I be worried about contact with animals?

Influenza viruses are not usually transmitted from animals to humans.

Birds, including wild birds and domesticated ducks, chickens and turkeys can become infected with influenza A viruses. Most of the avian (bird) influenza A viruses do not cause infection in humans. However, some avian influenza viruses can be transmitted to humans and can cause severe illness. Additional information on avian influenza is available at .

Some influenza A viruses can cause illness in pigs—these viruses are called “swine flu viruses”. While swine flu viruses do not normally infect humans, a small number of swine influenza virus infections occur in humans each year. Most human cases of swine influenza infections have occurred in people who have had contact with swine on farms or at fairs or other livestock shows. Additional information on swine influenza may be found at:  .

Dogs can become infected with an influenza A (H3N8) virus. This influenza virus can be transmitted from dog to dog, but does not cause illness in humans. More information on canine influenza may be found at: .

How can I get more information about influenza?


September 2013