How Does the Flu Spread?

Published June 21st, 2022 by Chris Riley
Fact Checked by
Jacqueline Hensler
Medically Reviewed:
Dr. Angel Rivera

The flu is a highly contagious virus that can cause severe illness. It spreads most often through contact with respiratory secretions, such as saliva droplets, mucus, or blood, from an infected person.

The virus can also be spread through contact with objects or surfaces that have been contaminated with the flu virus.

Symptoms of the flu include fever, cough, sore throat, body aches, headache, and fatigue as well as others that we will highlight below.

The flu is most commonly spread during the winter months, which is known as "flu season," although you can get it any time of year.

In this article, we will discuss how the flu spreads and how to protect yourself from it.

What is the flu?

The influenza virus, also called the flu, is a respiratory illness caused by viruses that affect your nose, throat, and lungs.

The flu can cause mild to severe illness in people of all ages although it occurs the most in children and the least in adults over 65.

woman with the flu

It is usually seasonal, occurring in the fall and winter months although you can get it any time of the year.

According to a Centers for Disease Control and Prevention (CDC) study published in Clinical Infectious Diseases (CID), approximately 8% of the population gets the flu every year although it can range from 3%-11% depending on the year based on an estimation of hospitalization rates.

What are the symptoms of the flu?

Flu symptoms can range from mild to severe and can even lead to death in the worst-case scenarios.

The symptoms of the flu usually have a rapid symptom onset time and can leave you feeling very sick within hours.

The most common symptoms of the flu include:

  • Fever
  • Chills
  • Muscle aches and pain
  • Headache
  • Fatigue or tiredness
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Nausea
  • Vomiting
  • Diarrhea

If you have these symptoms, you need to seek medical attention from your doctor as soon as possible as early diagnosis and treatment of the flu can help prevent serious complications.

How does the flu spread?

The flu is a highly contagious respiratory illness and the most common way it is spread is through person-to-person contact via respiratory droplets in the air when an infected person coughs, sneezes, or talks.

You can spread it to people up to six feet away from you and they get it by inhaling the droplets through their mouth or nose or if it lands in their eyes.

Other ways of getting the flu are by touching something that has the flu virus on it and then touching your eyes, nose, or mouth.

The virus can live on these surfaces for up to 48 hours after contact unless they get disinfected.

The flu virus can also be spread through contact with infected respiratory secretions like saliva, mucus, or blood.

How long am I contagious?

You are usually contagious from the day before symptoms start until about a week after you get sick.

It is believed the most contagious period when you have the flu is the first three to four days from when you had symptoms due to the fact that this is when you will cough the most which is the main way the flu spreads.

Children or adults with a weakened immune system may be able to infect others for even longer than the normal week of being contagious as their bodies take longer to fight off the virus.

Your symptoms will usually begin to show anywhere from one to four days after you become infected which means you can be contagious before you show any symptoms.

It is also possible that you can have the flu and be asymptomatic, meaning you show no symptoms of the flu yet still have the virus and can infect other people.

How do I tell when I am no longer contagious anymore?

The best way to tell is by how long your symptoms last. When you have the flu you will be contagious for at least a week or as long as your symptoms persist.

Once your symptoms have resolved and you are feeling better, it is safe to say that you are no longer contagious. Your fever can also be an indicator of whether you are contagious anymore.

If your fever goes down and your body temperature stays in the normal range for over 24 hours without the aid of medicines then you are no longer contagious.

What are the complications caused by the flu?

The flu can cause a number of different complications depending on how severe it is and your age, health status, and underlying medical conditions.

The most common complication from the flu is pneumonia which is an infection of the lungs that can be very serious and even lead to death. Other risks of complications caused by the flu include:

  • Ear infections
  • Sinus infections
  • Bronchitis
  • Worsening of asthma symptoms

If you have underlying chronic medical conditions such as congestive heart failure or diabetes, the flu can also exacerbate these conditions.

What do flu medicines do?

According to the CDC, there are four flu medicines approved by the Food and Drug Administration (FDA) that they recommend for treating the flu. The four flu medications are as follows:

  • Oseltamivir phosphate (available as a generic version and as the brand name Tamiflu)
  • Zanamivir (Relenza)
  • Peramivir (Rapivab)
  • Baloxavir marboxil (Xofluza)

These medications will help treat the flu and possibly shorten the amount of time you have it; however, you will still be contagious until you no longer show symptoms.

How do I prevent the flu?

The best way to prevent the transmission of influenza is by getting a yearly flu vaccine.

The CDC and experts recommend that everyone over the age of six months get a yearly flu vaccine with rare exceptions which has been their policy for over a decade now.

There are three types of vaccines available: the quadrivalent inactivated influenza vaccine (IIV4) which protects against four different flu viruses, recombinant influenza vaccine (RIV4), which does not use chicken eggs in the process of making it for those who are allergic to them, or live attenuated influenza vaccine (LAIV4), which distributes a weakened form of the virus via a nasal spray.

Another way to prevent getting the flu is by practicing healthy habits that stop the spread of germs such as washing your hands regularly, avoiding close contact with infected individuals, and covering your mouth and nose when you sneeze or cough.

What are the differences between COVID-19 and the flu?

There are a number of different ways to distinguish between COVID-19 and the flu.

For one, the coronavirus pandemic is caused by a novel coronavirus while the flu is caused by influenza viruses.

Additionally, COVID-19 symptoms tend to be more severe with a higher chance of developing complications such as pneumonia whereas the flu is typically less severe.

Finally, COVID-19 has a longer incubation period which means you can be infected with the virus and not show any symptoms for up to 14 days.


The flu is a virus that primarily affects the respiratory system and is highly contagious.

It is mainly spread through coughing, sneezing, or close contact with someone who has it or by touching a surface that contains the virus.

The incubation period for the flu is typically one to four days and the symptoms of the flu include fever, cough, sore throat, runny nose, body aches, and fatigue.

The flu can also lead to complications such as pneumonia.

You are normally contagious for about a week and you are no longer contagious once your symptoms have resolved and you have been fever-free for over 24 hours without the aid of medication.

The best ways to prevent the flu are to get your yearly flu vaccine and by practicing healthy habits such as washing your hands, covering your mouth and nose when you cough or sneeze, and by avoiding direct contact with sick people who already have it.

If you have any more questions regarding the flu, please talk to your doctor or health care provider.

Reference, Studies, and Sources:

Clinical Infectious Diseases



Mayo Clinic