Infectious Disease


Questions and Answers about the Seasonal Flu 

    The Flu Ends with You

What is seasonal influenza (flu)?
Seasonal influenza, commonly called “the flu,” is caused by influenza viruses, which infect the respiratory tract (i.e., the nose, throat, lungs). Unlike many other viral respiratory infections, such as the common cold, the flu can cause severe illness and life-threatening complications in many people. In the United States, on average 5% to 20% of the population gets the flu and more than 200,000 people are hospitalized from seasonal flu-related complications. Flu seasons are unpredictable and can be severe. Some people, such as older people, young children, pregnant women, and people with certain health conditions, are at high risk for serious flu complications.

What are the symptoms of the flu?
The flu can cause mild to severe illness, and at times can lead to death. The flu is different from a cold. The flu usually comes on suddenly. For information about flu symptoms, see Flu Symptoms & Severity.

When is the flu season in the United States?
In the United States, flu season occurs in the fall and winter. The peak of flu season has occurred anywhere from late November through March. The overall health impact (e.g., infections, hospitalizations, and deaths) of a flu season varies from year to year. CDC monitors circulating flu viruses and their related disease activity and provides influenza reports (called “FluView”) each week from October through May. See Weekly U.S. Influenza Summary Update. 

When is the flu season in the United States?
In the United States, flu season occurs in the fall and winter. The peak of flu season has occurred anywhere from late November through March. The overall health impact (e.g., infections, hospitalizations, and deaths) of a flu season varies from year to year. CDC monitors circulating flu viruses and their related disease activity and provides influenza reports (called “FluView”) each week from October through May. See Weekly U.S. Influenza Summary Update. 

How does the flu spread?
People with flu can spread it to others up to about 6 feet away. Most experts think that flu viruses are spread mainly by droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth or nose.

How long are people contagious?
Most healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Children may pass the virus for longer than 7 days. Symptoms start 1 to 4 days after the virus enters the body. That means that you may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Some persons can be infected with the flu virus but have no symptoms. During this time, those persons may still spread the virus to others.


How do I avoid catching the flu?
To avoid flu germs, people should wash their hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub. Linens, eating utensils, and dishes belonging to those who are sick should not be shared without washing thoroughly first. Eating utensils can be washed either in a dishwasher or by hand with water and soap and do not need to be cleaned separately.

The seasonal flu vaccine is available from:

  • Private physicians
  • Clinics
  • Local drug stores and pharmacies
  • Local grocery stores


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