What are the first signs of the flu?


The flu often begins with a mild muscle ache, a mild sore throat, or a feeling of tiredness that you just can't go away. Common sense dictates that treating the flu at the first symptoms can shorten the duration and severity of the illness. In recent years, several prescription drugs have been approved for this same purpose.

Even if you can't take these medications by recognizing the early signs and symptoms of the flu, you can act faster, not only by getting the bed rest you need, but also by taking steps to prevent the spread of infection to others.

Ellen Lindner / Get Medication Information


Finding the early signs and symptoms of the flu can help you seek treatment that shortens the course of the infection. The most common first symptoms are :

  • Sudden high fever (over 100.4 degrees Fahrenheit)
  • Shaking chills
  • Generalized muscle pain
  • Malaise (malaise)
  • Fatigue
  • Headache (usually spreads over the forehead and behind the eyes)

When full- blown acute symptoms develop, there is really nothing you can do but rest and let the disease run its course.


Influenza is caused by a family of viruses that affect the respiratory system . Unlike the common cold, which can be caused by several different viruses (including rhinoviruses, adenoviruses, and coronaviruses), influenza is caused exclusively by influenza viruses (called influenza type A, B, C, or D ).

When the first symptoms of the flu appear, it can be difficult to tell them apart from the first signs of a cold. But there are several key ways to tell them apart.

Influenza viruses almost always have a shorter incubation period , which means that symptoms tend to develop rapidly and violently, usually within a day or so. Because of this, the immune system will react more aggressively, flooding the body with inflammatory compounds to help neutralize the virus.

This aggressive immune attack will present with symptoms that are generally more severe and / or less common than the common cold .

Differences between colds and flu
Cold symptoms Flu symptoms
Incubation period 2-3 days 1-2 days
Onset of symptoms Gradually 4 to 7 days of exposure Quick exposure from 1 to 3 days
Hot Rare Often times, it lasts 3 to 4 days.
Shaking chills Rare general
Headache Sometimes it is usually associated with sinus congestion. Common, more related to inflammation of the whole body.
Sneezing and nasal congestion. general Occasionally
Cough Simple, mild to moderate Normal, often severe
Throat pain Occasionally general
Fatigue Sometimes mild to moderate Normal, often severe

Stages of infection

Influenza develops in stages , the initial stage is called the incubation phase and the last is called the acute phase.

The incubation phase is the time elapsed from infection until the first symptoms appear. It is during this phase that the virus will actively replicate and thus trigger the release of protective proteins called cytokines . Cytokines are pro-inflammatory, which means that they induce the body to induce inflammation so that tissues and blood vessels can swell to accommodate larger immune cells (known as monocytes ) .

In the second half of the incubation phase, subtle symptoms will begin to develop. These early symptoms are called prodromal and serve as a warning sign of an ongoing infection.

After the prodromal phase, the acute phase begins, which lasts between two and three days with all the symptoms of the "classic" flu. Most flu symptoms go away after about a week, but the cough can persist for up to two weeks.

A Guide to Talking to Your Doctor About Colds and Flu

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Flu can usually be diagnosed by symptoms alone, especially during flu season . This is especially true for prodromal flu symptoms, during which treatment is often presumed. Even if a rapid flu test (RIDT) is available, it is not as sensitive and can regularly give false negative results .

To prevent complications and further spread of the infection, a physician or telemedicine physician can prescribe some prescription flu medications over the phone without meeting in person.

Watch out

Unlike the common cold, for which there is no cure, the flu can be shortened by a day or two if certain antiviral medications are taken within 24 to 48 hours of the first symptoms. The drugs work by slowing down the replication of the virus and therefore potentially reducing the duration and severity of the disease .

However, medications do not always work, often because people miss the first signs of illness and appear too late. If not taken within the first 24 to 48 hours, the medications are likely to be of some benefit.

The U.S. Food and Drug Administration (FDA) has approved four antiviral treatment options:

For people at high risk for complications from influenza (including young children, the elderly, pregnant women, and people with chronic illnesses), taking an antiviral medicine can mean the difference between being hospitalized and recovering at home.

Get the word of drug information

The best way to deal with annual flu outbreaks is to avoid getting infected. The most effective strategy for this is to receive an annual flu shot or FluMist (nasal flu shot). The Centers for Disease Control and Prevention (CDC) recommends an annual flu vaccine for everyone 6 months and older, ideally by the end of October.

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