How Long Is the Flu Contagious?

A Deeper Look Into How the Flu Spreads

If you have been exposed to someone with the flu, you may be concerned about catching it. You may also wonder how long it takes to get sick after you have been exposed and how long you are contagious when you have it.

Flu Incubation Period
Verywell / Joshua Seong

Flu Incubation Period

The typical flu incubation period—the time between exposure and the start of symptoms—is between 24 hours and four days, with the average being two days. This means that if you are exposed to the influenza virus and become infected, you will start to experience flu symptoms, such as fever and body aches, anywhere between 24 hours and four days after the exposure.

When Are You Contagious?

Another factor that contributes to how the flu spreads is when exactly you may be contagious. Unlike many common illnesses that are only contagious when you're experiencing symptoms, the flu can be contagious 24 hours before your symptoms appear, so you're likely out there spreading the virus before you ever know that you have it. Add that to the number of people who try to push through their symptoms and expose others to their germs when they are sick, and it's easy to see why the flu affects so many people each year.

After symptoms start, adults can spread the virus for five to 10 days. However, the amount of virus spread decreases significantly after three to five days. Adults are most contagious with the flu from 24 hours before symptoms start to three to five days afterward.

Children can spread the virus for longer—up to 10 days, and sometimes even beyond that. People who have serious immune system problems can spread influenza for weeks, or even months, after they get it.

Flu symptoms generally don't come on gradually. More often, people describe the onset of the flu as if they were "hit by a truck." You feel fine, and then suddenly, an hour later, you feel like you can hardly move. The flu is definitely not just a bad cold—it is something else entirely.

How Does the Flu Spread?

During the cold winter months, the flu spreads rapidly. We know that it is highly contagious and can be spread before you even have symptoms. But do you know how it is spread and passed from person to person so easily?

Contrary to popular belief, it's not due to cold weather. Although the cold, dry air may mean the virus moves and infects people more easily, it does not actually cause the illness. It's also not really spread through the air the way many people think it is.

Droplet Transmission

Influenza is spread through droplets, which means if you cough, sneeze, or get any droplet matter from your respiratory system onto anything, it can be spread to someone else. This can happen in two ways.

First, if you sneeze, cough, or talk, microscopic droplets are released into the air as far as 6 feet away from you. Anyone around you can breathe in those droplets that contain the influenza virus.

Another possibility is that those droplets you sneezed, coughed, or breathed out land on objects and the next person that touches that object and then touches their eyes, mouth, or nose can be infected. If that person's immune system isn't able to kill off the virus, he or she will develop symptoms within one to four days of being infected. They are also now spreading the virus themselves, even before symptoms start.

Protecting Yourself and Others

Most people know they should stay home when they are sick with something like the flu (although many people don't). However, it's pretty difficult to avoid passing the virus if you don't even know you have it yet.

This is one of the reasons flu vaccines are so important. If you are vaccinated against the flu, your body will have a chance to fight it off before it spreads in your body and you are less likely to pass it on to other people or get sick yourself.

If you do get sick, stay home.

Know when to call in sick to work, wash your hands frequently, and make sure those that come into contact with you do the same. Cover your cough and do everything you can to avoid being around people that are at high risk for serious complications from the flu.

Preventing the spread of the flu virus is up to all of us. Even if you think it won't be serious for you if you get it, it might be for someone you pass it to.

Preventing the Flu After Exposure

Although there are various products and remedies that may claim to help prevent illness once you've been exposed to the flu, none of them have proven to be effective. Your best bet to prevent the flu is to get your annual flu vaccine. Although it's not 100 percent effective at preventing the flu, it gives you a much better chance of avoiding the illness than anything else.

If you are exposed to someone with the flu, avoid close contact with the person and wash your hands frequently.

  • Vitamin C: Although vitamin C is widely used and has many benefits, there is no scientific proof that it will help you avoid an illness such as the flu or a cold.
  • Humidifiers: Evidence suggests that viruses such as the cold and flu spread more easily in cold, dry air. This is one of the reasons that they're more common during the winter. Running a humidifier in your home during the winter can help keep your nasal passages moist. And while there's no guarantee that this will prevent you from getting sick, it can't hurt (as long as you keep it properly cleaned).
  • Antiviral medications: If you're at high risk for complications from the flu and you know you were exposed to it, talk to your healthcare provider about taking antiviral medications. It can help prevent influenza in some people and will reduce the severity of the symptoms in those who do get it.

A Word From Verywell

Of course, do your best to avoid getting the flu at all. Be sure to get your flu vaccine, wash your hands often, and avoid people who are sick with the flu. The flu is not something to take lightly and if you do get it, stay away from other people when you are sick.

Frequently Asked Questions

  • How long does it take to develop the flu after exposure?

    The incubation period for the flu ranges from one to four days. If you were exposed to the flu and contracted it, you would experience symptoms within four days.

  • When is the flu contagious?

    The influenza virus is contagious from about 24 hours before symptoms appear for up to 10 days after. The virus is most contagious before symptoms and during the first three to five days.

    Influenza commonly circulates in the United States between October and April.

  • Can you be around someone with the flu and not catch it?

    Yes, being exposed to the flu does not automatically mean you will catch it. If you have gotten your annual flu shot, you are significantly less likely to contract the flu. Practicing good hand hygiene can help to prevent catching the flu. Wash your hands frequently and avoid touching your mouth, nose, or eyes.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. US Centers for Disease Control & Prevention, "Key Facts About Influenza (Flu)"

  2. National Health Service (UK), "How long is someone infectious after a viral infection?"

  3. US Centers for Disease Control & Prevention, "How Flu Spreads"

  4. US Centers for Disease Control & Prevention, "Flu: What To Do If You Get Sick"