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Flu Facts

What is the flu?

The flu (short for "influenza") is an illness caused by viruses. Flu viruses can infect a person's nose, throat, and lungs.

When is flu season?

In New England, flu season usually begins in December and lasts through March.

Is the flu dangerous?

The flu can be a serious illness. Every year, 12,000 to 79,000 people living in the United States die from flu-related complications.

Anyone can get the flu, but some people can become very sick. According to the CDC, people at highest risk for becoming very sick from the flu include:

  • Children younger than 5, but especially children younger than 2.

  • Adults age 65 and older.

  • Pregnant women and women up to two weeks postpartum.

  • People with certain medical conditions, such as asthma, diabetes, or chronic lung disease.

  • Residents of nursing homes and other long-term care facilities.
  • American Indians and Alaska Natives
Most people recover from the flu within 1 to 2 weeks. To learn more, see People at High Risk of Developing Flu-Related Complications from the CDC.

How is flu spread?

Flu viruses live in the nose and throat of an infected person. When an infected person coughs, sneezes, or talks, flu viruses are spread into the air. People nearby can breathe in the viruses and become sick. An infected person can spread the flu a day before symptoms appear and can remain contagious for up to a week later. A child with flu can be contagious longer than a week.

What are flu symptoms?

Flu symptoms appear 1 to 5 days after exposure, and may include:

  • Fever (102° to 104°), lasting 3 to 5 days

  • Chills

  • Headaches

  • Sore throat

  • Severe muscle aches

  • Tiredness, which can be extreme and can last two weeks or more

  • Dry cough

  • Runny or stuffy nose

Serious complications from flu include dehydration, pneumonia, bronchitis, and sinus and ear infections. Flu infection can also make chronic health problems worse.

Who should get vaccinated?

Anyone who wants to reduce their risk of getting the flu should get vaccinated. However, during flu seasons when vaccine supplies are limited or delayed, priority should be given to people at high risk for becoming very sick from the flu and their caregivers.

To learn more, see Who Needs a Flu Vaccine or When from the CDC.

If you get a flu shot can you still get the flu?

The flu shot is 40% to 60% effective in preventing flu or at least reducing symptoms. It usually takes two weeks after the shot to develop maximum protection, which then gradually wears off.  The flu shot does not cause the flu. To learn more, see How Well Does the Flu Vaccine Work from the CDC.


Sources: Centers for Disease Control and Prevention, Cambridge Public Health Department (Public Health Nursing Program), Massachusetts Department of Public Health, and Boston Public Health Commission.

Updated September 16, 2020


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