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Flu

Sources: FLU.gov and the CDC's Seasonal Flu Page.

What is Flu? | How does Flu spread? | Flu vaccines | Fact Sheets | More Flu resources

About the Flu:

Seasonal flu is a contagious respiratory illness caused by flu viruses. Approximately 5-20% of U.S. residents get the flu each year.  The best way to prevent the flu is by getting a flu vaccine each year.

  • Flu season typically peaks in January or February.
  • Getting the flu vaccine is your best protection against the flu.
  • Flu-related complications include pneumonia and dehydration.
  • Illness from seasonal flu usually lasts one to two weeks.

What is the seasonal flu?

Seasonal flu is a contagious respiratory illness caused by flu viruses. It spreads between people and can cause mild to severe illness. In some cases, the flu can lead to death.

When is flu season?

In the United States, flu season occurs in the fall and winter. Seasonal flu activity usually peaks in January or February, but it can occur as early as October and as late as May.

 How does seasonal flu spread?

Most experts believe that you get the flu when a person with the flu coughs, sneezes, or talks and droplets containing their germs land in your mouth or nose. You can also get the flu by touching a surface or object that has the flu virus on it and then touching your mouth, eyes, or nose.

Signs and symptoms of flu

People who have the flu often feel some or all of these signs and symptoms:

  • Fever* or feeling feverish/chills
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle or body aches
  • Headaches
  • Fatigue (very tired)
  • Some people may have vomiting and diarrhea, though this is more common in children than adults.

*It’s important to note that not everyone with flu will have a fever.

Who is at risk?

Some groups are more likely to experience complications from the seasonal flu, including:

How can I protect myself from seasonal flu?

Get the flu vaccine as soon as it is available in your area. The 2012-2013 vaccine is now available.

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

  • “Flu shots” — inactivated vaccines (containing killed virus) that are given with a needle. There are three flu shots being produced for the United States market now.
    • The regular seasonal flu shot is “intramuscular” which means it is injected into muscle (usually in the upper arm). It has been used for decades and is approved for use in people 6 months of age and older, including healthy people, people with chronic medical conditions and pregnant women. Regular flu shots make up the bulk of the vaccine supply produced for the United States.
    • A hi-dose vaccine for people 65 and older which also is intramuscular. This vaccine was first made available during the 2010-2011 season.
    • An intradermal vaccine for people 18 to 64 years of age which is injected with a needle into the “dermis” or skin. This vaccine is being made available for the first time for the 2011-2012 season.
  • The nasal-spray flu vaccine — a vaccine made with live, weakened flu viruses that is given as a nasal spray (sometimes called LAIV for “Live Attenuated Influenza Vaccine”). The viruses in the nasal spray vaccine do not cause the flu. LAIV is approved for use in healthy* people 2 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 flu-like illnesses caused by non-influenza viruses.

The seasonal flu vaccine protects against the three influenza viruses that research suggests will be most common.

You should also follow our everyday steps to keep yourself healthy.

What are common complications from the seasonal flu?

Complications from the flu include:

Each year approximately 5-20% of U.S. residents get the flu and more than 200,000 people are hospitalized for flu-related complications.

How long does the illness last?

Most people who get the flu feel much better within one or two weeks.

How long am I contagious?

Most healthy adults can infect others one day before symptoms develop and five to seven days after symptoms appear. Some people, especially young children and people with weakened immune systems, might be contagious for a longer period.

How many times can a person become infected with the seasonal flu?

You are unlikely to get infected with the same exact strain of flu more than once. It is possible to be infected with flu virus more than once in a season, though, because several different strains of flu virus circulate each year. Exposure to a particular strain of flu virus may help protect you against that strain in the future. But it will not protect you from infection with other flu virus strains.

Is the stomach flu really the flu?

Many people use “stomach flu” to describe illness with nausea, vomiting or diarrhea. Many different viruses, bacteria, or parasites can cause these symptoms. While the flu can sometimes cause vomiting, diarrhea, and nausea—more commonly in children than adults — these problems are rarely the main symptoms of the flu. The flu is a respiratory disease and not a stomach or intestinal disease.

Who monitors seasonal flu activity?

The Centers for Disease Control and Prevention (CDC) tracks flu activity in the United States year round and produces a weekly report of flu activity from October through mid-May.

Fact sheets:

For more information: