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What is the Flu Incubation Period?

By J.M. Densing
Updated May 17, 2024
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The term "flu incubation period" refers to the time it takes from exposure to the influenza virus until the beginning of observable symptoms. This time frame can vary depending on the strain of flu virus, and typically is from one to four days. During the incubation period, the exposed person is usually able to transmit the virus to others. It's a good idea to use basic infection prevention strategies during flu season just in case.

The flu illness is caused by the influenza virus. There are two main types, known as A and B. These viruses are constantly mutating, or changing, which adds to the risk of infection; the H1N1 flu virus is thought to be a mutation of influenza A. The time from exposure to the virus until the initial flu symptoms is the incubation period.

The flu incubation period is usually one to four days; for H1N1, it may be about four to seven days. It can vary depending on the strain and the health of the exposed person, but the average time is two days. The incubation period is often shorter for a person in poor health since his or her body is already in a weakened state and less able to fight the virus. During this period, the person may show no symptoms.

It is possible for a person to spread the influenza virus to others during the flu incubation period,. The most common way is when an infected person coughs or sneezes, thereby releasing tiny droplets of moisture containing the virus into the air that a healthy individual breathes it in. Since this can happen during the incubation period while a person is unaware of an infection, it's important to remember to cover sneezes and coughs. The best way to do this is to cough or sneeze into the bend of an elbow rather than the hand, since this can help to prevent spreading the virus through touch.

At the end of the flu incubation period, a person will usually start to develop symptoms including sudden fever, coughing, body aches, and sore throat. The ill person is also able to continue infecting others for at least another five to seven days and may even spread the flu virus for longer periods. As a result, it's a good idea to practice basic prevention strategies such as getting a seasonal flu shot, frequent hand washing, minimizing contact with those who are sick, and covering coughs and sneezes.

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Discussion Comments
By burcidi — On Jan 29, 2014

@SarahGen-- I just read a news article about this. It said that the average flu incubation period is two days. That's not a lot of time at all. And most people are contagious even before they have symptoms. I guess that's how flu spreads so easily.

The incubation period of flu can go up to seven days depending on the strain. There are actually lots of different flu strains and they change from year to year. (That's why we get a new flu shot every year). The new strain that was in the news a lot in 2013, swine flu also has an incubation period of two to four days. But this type of flu tends to be more severe and can be life threatening.

Although there is no treatment for flu, it's a good idea to see a doctor if the symptoms are severe. Complications can be prevented by using fever reducers and staying hydrated..

By bear78 — On Jan 28, 2014

@SarahGen-- Yes, it can.

Like the article said, the incubation period is between one and four days. It's more likely for it to be three or four days, but it's not impossible to develop flu symptoms in just one day.

I suggest staying home and resting and drinking lots of water. Avoid contact with people, especially kids, because you are contagious right now.

By SarahGen — On Jan 27, 2014

I spent time at a kindergarten yesterday and today I feel kind of sick. I'm tired, I have a headache and my body hurts. Can flu develop so quickly though?

By Talentryto — On Jan 26, 2014

During this time of year when the flu is prevalent in many regions around the world, it is important to pay close attention to the onslaught of symptoms. If you catch flu symptoms early, there are medications available that may possibly shorten the duration of the flu if you indeed have the virus. Knowing the incubation period for the flu will help you know what and when to expect, especially if you have been around people with full-blown flu symptoms.

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