What Is the Flu Incubation Period?

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If you have been exposed to someone with the flu, you are probably 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.

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. Now that you know how long the flu incubation period lasts, you will know what to expect if you are exposed to it.


"Clinical Signs and Symptoms of Influenza." Seasonal Influenza (Flu) 01 Jul 09. US Centers for Disease Control and Prevention. Department of Health and Human Services. 05 Sep 12.

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