Influenza (Flu)

What is influenza?

Influenza is commonly referred to as “the flu.” It is a contagious respiratory illness caused by influenza viruses. Flu can cause mild to severe illness, and at times can lead to death. There are two main types of flu viruses: Type A and B. Each type includes many different strains that tend to change from year to year. Flu viruses can be detected year-round in the United States, but they are most common during the fall and winter.

Who gets flu?

Anyone can get flu, but it is more likely to cause serious illness in young children, pregnant women, people aged 65 years and older, residents of nursing homes and other long-term care facilities, and people with chronic illnesses (e.g., lung disease, heart disease, cancer, or diabetes) or weakened immune systems.

How is flu spread?

Flu spreads mainly by droplets from the nose or throat that are released when an infected person coughs, sneezes or talks. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might get flu by touching a surface or object that has the flu virus on it and then touching his or her mouth, nose, or eyes. Flu can spread from one person to another beginning about one day before symptoms start and up to five to seven days after becoming sick.

What are the symptoms of flu?

Flu symptoms can include a sudden onset of fever or feeling feverish/chills, cough, sore throat, runny or stuffy nose, headache, fatigue, and muscle or body aches. In children, vomiting and diarrhea might occur. Most people with flu recover within a few days to less than two weeks. Some people might develop severe or even life-threatening complications, such as pneumonia.

How soon after exposure do symptoms appear?

Symptoms usually appear 1–4 days after exposure.

How is flu diagnosed?

Doctors usually diagnose flu based on symptoms and they might use laboratory tests for influenza. Many doctors might not test for flu because the test results usually do not change how you are treated.

What is the treatment for flu?

Rest, liquids, and over-the-counter medicines for fever and discomfort are the usual treatments. Prescription antiviral drugs are available and can 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. Antibiotics are not used to treat flu.

How can flu be prevented?

You can take three important steps to fight the flu:

  1. Get vaccinated every year.
  2. Stop the spread of flu and other germs.
    • Cover your mouth and nose with a tissue when coughing or sneezing.
    • Wash your hands often to help protect yourself from germs.
    • Avoid touching your eyes, nose or mouth.
    • Stay home from work, school, and other activities when you are sick.
    • Avoid close contact with people who are sick.
    • Clean surfaces and objects that might be contaminated with germs.
  3. Take flu antiviral drugs if your doctor prescribes them.

Who should be vaccinated against flu?

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

  • Pregnant and people up to 2 weeks after the end of pregnancy, or those who plan to be pregnant during the flu 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, COPD, anemia, cancer, weak immune systems (including those with HIV), or a seizure disorder.

To help prevent the spread of flu 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 be vaccinated. Travelers to countries outside the United States might also need to consider flu 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 flu virus are circulating. Also, protection offered by the flu vaccine typically only lasts for several months.

Should I be worried about contact with animals?

Flu viruses are not usually transmitted from animals to humans.

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

Some type A flu viruses can cause illness in pigs. These viruses are called “swine flu viruses.” Although swine flu viruses do not normally infect humans, a small number of swine flu virus infections occur in humans each year. Most human cases of swine flu infections have occurred in people who have had contact with swine on farms or at fairs or other livestock shows. Additional information on swine flu is available at

Dogs can become infected with canine (dog) flu A viruses (H3N8 and H3N2). These dog flu viruses can be transmitted from dog to dog, but they do not cause illness in humans. More information on canine flu is available at

How can I get more information about flu?

September 2018