What Is the Flu Incubation Period?

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If you have been exposed to someone with the flu, you may be concerned about catching it. So how long is the typical flu incubation period -- meaning, how long after exposure until you get sick?

What To Expect

The typical flu incubation period is between 24 hours and 4 days, with the average being 2 days.

What this means is that if you are exposed to the influenza virus and become infected, you will start to experience flu symptoms anywhere between 24 hours and 4 days after the exposure.

Flu symptoms generally don't come on gradually. More often, people describe the onset of 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.

When Is the Flu 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 a day before you get sick -- 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 work anyway, and it's easy to see why the flu affects so many people each year.

After symptoms start, adults can still spread the virus for 5 to 10 days. However, the amount of virus spread decreases significantly after 3-5 days.

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.

How Does the Flu Spread?

During the cold winter months, the flu (influenza) 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? Do you know how the flu is 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 six 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.

Spreading the Virus

If that person's immune system isn't able to kill off the virus, they will develop symptoms within 1 to 4 days of being infected. They are also now spreading the virus themselves - even before symptoms start.

If you have the flu, you can spread it up to one day before your symptoms develop and 5 to 7 days after you get sick. Children who have the flu can spread the virus for longer than 7 days.

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.

Can I Prevent 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% 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 health care provider about taking antiviral medications. They can help prevent influenza in some people and will reduce the severity of the symptoms in those who do get it.

Of course, you want to do your best to avoid getting the flu at all. So be sure to get your flu vaccine, wash your hands often, and avoid people who are sick with the flu. 


How Flu Spreads| Seasonal Influenza (Flu) | CDC. https://www.cdc.gov/flu/about/disease/spread.htm. 

Key Facts about Influenza (Flu) | Seasonal Influenza (Flu) | CDC. http://www.cdc.gov/flu/keyfacts.htm.  

Prevention and Control of Seasonal Influenza with Vaccines | Health Professionals | Seasonal Influenza (Flu). http://www.cdc.gov/flu/professionals/acip/index.htm. 


The Flu: What To Do If You Get Sick. Centers for Disease Control and Prevention. http://www.cdc.gov/flu/takingcare.htm. Published May 26, 2016. 

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