How Long is the Flu Contagious?

Published June 23rd, 2022 by Chris Riley
Fact Checked by
Jacqueline Hensler
Medically Reviewed:
Dr. Angel Rivera

The flu is a highly contagious respiratory infection that can cause a number of unpleasant symptoms, including fever, body aches, headache, and fatigue, and can also lead to more serious complications like pneumonia.

If you have the flu, it is important to know how long you are contagious so that you can take the necessary precautions to prevent the spread of the virus.

In this article, we will answer some common questions about the flu including how long you are contagious, review the best treatment options available, and provide tips on how to prevent getting and spreading the flu virus.

What is the flu?

The flu, which is short for influenza, is a contagious respiratory illness caused by several influenza viruses with symptoms ranging from mild to severe affecting your nose, throat, and lungs.

Complications from the flu include pneumonia, bronchitis, sinus infections, and ear infections, and it can prove fatal in some circumstances.

Every year 3%-11%, with an average of just over 8%, of Americans contract this viral infection and are symptomatic.

That number can be even more in some years according to a study by the Centers for Disease Control and Prevention (CDC) published in 2018. Another study estimates that 5%-20% of the population can get the flu which counts people who are both symptomatic and asymptomatic.

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Children are the most susceptible to the flu and can have more severe symptoms while adults aged 65 years and older are also at a higher risk for developing complications from the flu although you can contract it at any age.

The flu and the common cold are caused by different viruses and the flu is often more severe than the common cold with the symptoms coming on more suddenly too.

What are the symptoms of the flu?

The most common flu symptoms include the following:

  • Fever
  • Chills
  • Cough
  • Sore throat
  • Runny nose or stuffy nose
  • Body aches or muscle aches
  • Headaches
  • Fatigue
  • Vomiting
  • Diarrhea

Vomiting and diarrhea are more common symptoms in children although they can happen in adults too.

If you are experiencing these symptoms, please seek medical attention from your doctor or health care provider.

Your symptoms are more likely to last for a shorter time the sooner you get treatment.

What are the complications from the flu?

The flu can cause severe illness and sometimes death, especially in those with a high risk of influenza complications such as young children, the elderly, pregnant women, and if you have certain health conditions like asthma or diabetes.

The most common complication from the flu is bacterial pneumonia which is an infection of your lungs that can be very serious and even fatal.

Other complications can include bronchitis, sinus infections, and ear infections.

How is the flu diagnosed?

Your doctor will diagnose you with the flu based on your symptoms and sometimes a rapid test can be done in your doctor's office which will give results within minutes.

The rapid test, however, is not always accurate and your doctor may also recommend a laboratory test that can confirm the diagnosis.

How does the flu spread?

The flu is most commonly spread through person-to-person contact with respiratory droplets from coughing, sneezing, or talking and these droplets can land in the mouths, eyes, or noses of people who are nearby.

It can also be spread if you touch something that has been contaminated with these respiratory droplets, for example, doorknobs or light switches, and then touch your own mouth, eyes, or nose.

Sometimes the flu can also be spread through food that has been contaminated with respiratory secretions from an infected person although this is not very common.

How long is the flu contagious?

There is a rapid onset of symptoms when you have the flu and you are contagious for a day before they start.

You are most contagious with the flu during the first three to four days after your symptoms start but you can still spread the flu to others for up to a week after the first sign of symptoms.

If you have a weakened immune system, you may be able to spread the virus for even longer because it will take your body longer to fight it off.

How do I know if I am not contagious anymore?

If you have been diagnosed with the flu, you are no longer contagious if you do not have a fever for 24 hours without the aid of medication.

What are the treatment options for the flu and do they prevent the flu?

There are currently four antiviral drug treatment options recommended by the CDC but none of them prevent you from spreading the flu.

They can, however, help lessen the severity and duration of your symptoms. The four antiviral medications recommended by the CDC include:

  • Oseltamivir (Tamiflu)
  • Zanamivir (Relenza)
  • Peramivir (Rapivab)
  • Baloxavir marboxil (Xofluza)

These medications work best when they are started within 48 hours of your symptoms starting. Oseltamivir (Tamiflu) is also available in a generic form too.

How do you prevent the flu?

The best way to prevent the flu is by getting a yearly flu vaccine, preferably before flu season starts (October- May) or by the end of October although you can receive them at any time.

The CDC recommends that everyone six months of age and older need to get a flu shot every year with few exceptions. The vaccines available are quadrivalent vaccines that protect against four different influenza strains.

The quadrivalent vaccines are available as a shot (injected) or as a nasal spray. The three different vaccines available are as follows:

  • Quadrivalent vaccine (IIV4)
  • Recombinant vaccine (RIV4), which does not use egg products if you are allergic to eggs
  • Live attenuated influenza vaccine (LAIV4), which is a nasal spray that delivers weakened forms of the viruses so your immune system can build a response to them

Besides receiving your annual influenza vaccine, you can also help prevent the spread of the flu by:

  • Washing your hands often with soap and water for at least 20 seconds or using an alcohol-based hand sanitizer
  • Avoiding touching your eyes, nose, or mouth with unwashed hands
  • Avoiding close contact with sick people
  • Staying home when you are sick until you are no longer contagious to avoid the spread of germs
  • Cover your coughs and sneezes with a tissue and then throw the tissue in the trash, if you do not have a tissue, cough or sneeze into your upper sleeve or elbow rather than your hands
  • Clean and disinfect surfaces and objects that may be contaminated with germs like the flu

Doing these simple steps can help prevent the spread of the flu virus and other respiratory illnesses to you and other people.


The flu is a contagious respiratory illness caused by the influenza virus and it can cause mild to severe symptoms and sometimes lead to complications like pneumonia, bronchitis, or ear infections.

You can catch the flu by coming into contact with respiratory secretions from an infected person or touching contaminated surfaces and then touching your mouth, nose, eyes, or face.

You are contagious the day before your symptoms start and the flu is most contagious during the first few days of symptoms but you can still spread the flu to others for up to a week after you show initial symptoms.

Treatment options for the flu include antiviral medications which can help lessen the severity and duration of your symptoms but they will not prevent you from spreading the flu.

The best way to prevent the flu is by getting a yearly flu vaccine and by following the flu prevention listed above.

If you have any more questions about the flu and how long you are contagious, please talk to your doctor or health care provider.

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