Influenza (Flu)

Last Updated 08/08/2022

Authors:Janet R Maurer, MD, MBA, FCCP; De De Gardner, RRT, DrPh, FCCP; Bryan D Kraft, MD, FCCP; Corinne Young, NP-C, MSN, FCCP

About Influenza (Flu)

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The flu is a contagious respiratory illness caused by the influenza virus. It infects the upper respiratory tract and causes symptoms such as cough, fever, headache, body aches, sore throat, and runny nose. The flu is usually self-treatable and self-diagnosable, but rapid diagnostic tests for it are available at health-care facilities. If you’re otherwise healthy, then you can expect your flu-related symptoms to resolve within several days.

What you need to know

Although the flu may seem commonplace, it can be quite dangerous. Getting the flu, especially if you have a compromised immune system, can lead to pneumonia, and, in extreme cases, death. In fact, nearly 50,000 US deaths are caused by the flu every year.

How it spreads

Influenza is spread through tiny droplets made when people with the flu cough, sneeze, or talk. Once a person has become infected with the virus, they will be contagious for 1 day before and 7 days after symptoms appear. In other words, most people are infecting others before they even know they’re sick.

Person getting a flu shot

Preventing the Flu

Fortunately, receiving the flu vaccine every year reduces your risk of getting the flu by 40% to 60%. That’s why it’s so important to visit your health-care professional (HCP) and receive the vaccination every year at the beginning of September. However, because flu season can circulate as late as May, it’s really never too late to get your shot.

Even though you may never get sick, it’s important to remember that you can still be a carrier of influenza and can pass it to your family, friends, or close contacts. Receiving the influenza vaccine protects you, your loved ones, and the rest of your community.

Protect yourself and family from the Flu

Getting the flu shot reduces your risk of getting the flu by 40%-60% and reduces the risk of spreading it to others.

  • Catching the flu could lead to pneumonia and/or death.
  • ~50,000 people die of the flu each year.

Flu shot

Get vaccinated

Getting the flu shot reduces your risk of getting the flu by 40%-60% and reduces the risk of spreading it to others.

  • Catching the flu could lead to pneumonia and/or death.
  • ~50,000 people die of the flu each year.


Stop the spread

Limit spreading the flu by getting vaccinated, avoiding contact with others, practicing cough etiquette, and washing your hands frequently.

  • You could spread the flu for 2-7 days before feeling sick.

Lower your risk of getting the flu

Reduce risk

If you get the flu, the flu shot reduces your risk of developing complications.

Who is at risk for developing a severe complication from the flu?

  • Anyone with a chronic health condition
  • Adults 65 and older
  • Pregnant women
  • Children


Save Children

50% of children are less likely to die of flu if vaccinated.

  • Children have a higher mortality rate than healthy adults.
  • Children are more likely to have vomiting and diarrhea than adults with the flu.
  • Babies < 6 months cannot get the flu shot, so they depend on moms and adults to get the flu shot to protect them.

Did you know that influenza and pneumonia are the eighth-leading causes of death in the United States?

Flu Infographic

Flu Shot Mythbuster

Who’s at risk for developing a severe case of the Flu?

  • Children aged 6 months to 5 years and those not old enough to receive the vaccine (children aged <6 months)
  • Pregnant women
  • Adults aged at least 65 years
  • Anyone with a chronic health condition, especially those with asthma or chronic obstructive pulmonary disease
  • Adults who cannot receive vaccinations

How does the Flu affect children vs adults?

  • Children have a higher mortality rate from the flu than healthy adults
  • Children with the flu more commonly experience vomiting and diarrhea than adults
  • Children younger than 6 months are too young to receive the influenza vaccine, so they depend on adults to be vaccinated to protect them

Symptoms of the Flu

  • Fever or feeling feverish/chills (but not everyone with the flu will have a fever)
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle or body aches
  • Headache
  • Fatigue (tiredness)
  • Vomiting and diarrhea (more common in children than adults)

Examples of Flu-related complications

  • Bacterial pneumonia
  • Ear infections
  • Sinus infections
  • Worsening of chronic medical conditions like asthma

Ways to protect yourself during Flu season

  • Frequently wash your hands
  • Use hand sanitizer when in public areas
  • Avoid touching your eyes, nose, and mouth
  • Practice good cough etiquette (cough into your sleeve, not your hand)

Treating the Flu

  • Get plenty of rest
  • Drink lots of clear fluids
  • Take over-the-counter medications to control symptoms

I think I have the Flu. Now what?

If you think you have the flu, then it’s important to visit an HCP. Several influenza tests are available (called “rapid influenza diagnostic tests”). The tests involve swiping the inside of your nose or the back of your throat with a swab. The results are usually available within 1 hour. If your test result is positive, then your HCP may prescribe influenza antiviral drugs to help treat—but not cure—the flu.

Get the facts about Flu shots: Myths BUSTED


The flu shot will give me the flu.


The flu shot contains inactivated flu virus and can not give you the flu.


I had the flu last year, even though I got the flu shot.


Getting a flu shot is not a guarantee you will not get the flu, but it likely will reduce the severity of your illness.


I never get sick, so I don’t need a flu shot.


You can still be a carrier of the flu and pass it to your family and friends. Getting the flu shot protects you as well as your loved ones and the community.


I got the flu shot last year, so I don’t need one this year.


Everyone 6 months or older should get a flu shot once a year since the flu strains can change each year. The best time to get the shot is in the fall, but it is not too late to get the shot throughout the flu season.


I have a severe allergy to eggs, so I can’t get the flu shot.


There are flu shots without egg products. Your doctor can help you find the right one for you.


I have COPD and will get sicker with the flu shot.


The opposite is true. Patients with COPD or asthma who get the flu are more likely to have severe flare-ups of their COPD, be hospitalized, get pneumonia, or even die. These patients are at the highest risk and should get the flu shot.


I have my asthma under control, so I don’t need the flu shot.


Patients with mild or moderate asthma are at risk for serious flu complications. Because the airways are sensitive, the flu can cause inflammation leading to an asthma attack. Patients with asthma are more likely to develop pneumonia if infected with the flu.

Flu Shot Mythbuster

Where can I get more facts?

Patient video resources

The Importance of Herd Immunity
Influenza: Know the Facts

Am I or My Loved Ones Having Flu Complications?

Resources for clinicians

Clinician Infographic

Video resources

Herd Immunity
Complications of the Flu
Will This Give Me the Flu?
I Never Get the Flu
What Do You Do if Your Patient is Against Vaccinations?

Flu Symptoms, Complications, and Comorbidities
Treatment of Influenza
Influenza Vaccinations: Recommendations and Precautions
Don’t Take “No” for an Answer to the Flu Shot