Influenza (Flu) Fact Sheet

What Everyone Should Know About Flu and the Flu Vaccine

What is the flu?

The flu is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and at times can lead to death. The best way to prevent this illness is by getting a flu vaccination.

Every year in the United States , on average:

  • 5% to 20% of the population gets the flu;
  • more than 200,000 people are hospitalized from flu complications, and;
  • about 36,000 people die from flu.

Some people, such as older people, young children, and people with certain health conditions, are at high risk for serious flu complications.

What are the symptoms of the flu?

The flu usually starts suddenly and may include these symptoms:

  • fever (usually high)
  • headache
  • extreme tiredness
  • dry cough
  • sore throat
  • runny or stuffy nose
  • muscle aches
  • stomach symptoms, such as nausea, vomiting, and diarrhea, may occur in children but are rare in adults

Are some people at higher risk for complications than others from getting the flu?

People at high risk for serious flu complications include older people, young children and people with certain health conditions.

What are the complications associated with the flu?

Some of the complications caused by flu include bacterial pneumonia, dehydration and worsening of chronic medical conditions, such as congestive heart failure, asthma or diabetes. Children may get sinus problems and ear infections.

How is the flu spread?

The flu spreads in respiratory droplets caused by coughing and sneezing. It usually spreads from person to person, though occasionally a person may be infected by touching something with virus on it and then touching their mouth or nose.

When and for how long is a person able to spread the flu?

Adults may be able to infect others beginning one day before getting symptoms and up to seven days after getting sick. That means that you can give someone the flu before you know you're sick as well as when you are sick.

Who should get the flu vaccine?

When there is an adequate supply of vaccine, everyone should get the flu vaccine. Those people at greatest risk for complications of the flu and those most likely to get or spread the flu should be immunized as soon as vaccine is available. These include:

  • All children aged 6-59 months;
  • Adults aged ≥65 years of age;
  • Adults aged 50-64 years of age;
  • Persons aged 2-64 years with underlying chronic medical conditions;
  • Persons ≥ 2 years old with conditions that can cause breathing problems ;
  • All women who will be pregnant during the influenza season;
  • Residents of nursing homes and long-term care facilities;
  • Children aged 6 months to 18 years on chronic aspirin therapy;
  • All health care workers; and
  • Out-of-home caregivers and household contacts of persons in the high-risk groups.

Who should not be vaccinated?

There are some people who should not be vaccinated. They include:

  • People who have a severe allergy to chicken eggs.
  • People who have had a severe reaction to an influenza vaccination in the past.
  • People who developed Guillain-Barre syndrome (GBS) within six weeks of getting an influenza vaccine previously.
  • Children less than six months of age.
  • People who are sick with a fever. (These people can get vaccinated once their symptoms lessen. People with a mild illness can usually get the vaccine.)

Cold Versus Flu

What is the difference between a cold and the flu?

The flu and the common cold are both respiratory illnesses but they are caused by different viruses. Because colds and flu share many symptoms, it can be difficult (or even impossible) to tell the difference between them based on symptoms alone. Special tests that usually must be done within the first few days of illness can be carried out, when needed, to tell if a person has the flu.

What are the symptoms of the flu versus the symptoms of a cold?

In general, the flu is worse than the common cold, and symptoms such as fever, body aches, extreme tiredness and dry cough are more common and intense. Colds are usually milder than the flu. People with colds are more likely to have a runny or stuffy nose. Colds generally do not result in serious health problems, such as pneumonia, bacterial infections, or hospitalizations.

Preventing the Flu

What can I do to protect myself against the flu?

The single best way to prevent the flu is to get a flu vaccination each fall. There are two types of vaccines:

  • The "flu shot" -- an inactivated vaccine (containing killed virus) that is given with a needle. 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"). LAIV is approved for use in healthy people 5 years to 49 years of age who are not pregnant.

About two weeks after vaccination, antibodies develop that protect against influenza virus infection. Flu vaccines will not protect against influenza-like illnesses caused by other viruses.

Can antiviral medications prevent the flu?

Four antiviral drugs (amantadine, rimantadine, oseltamivir, and zanamivir) are approved for treatment and prevention of the flu. These drugs are not, however, a substitute for influenza vaccination. All of these drugs are prescription drugs and a doctor should be consulted before the drugs are used for treating or preventing the flu.