What Are Some of the First Symptoms of the Flu

When you get the flu (influenza), it will often start with mild muscle aches, a slight tickle in the throat, or a worn-out feeling you just can't shake. Common wisdom suggests that if you treat flu when symptoms first appear, you may be able to shorten the duration and severity of the illness. In recent years, a number of prescription drugs have been approved for just such a purpose.

Even if you are unable to get these medications, by recognizing the early signs and symptoms of flu, you can act quicker—not only getting the bed rest you need, but to take steps to prevent the spread of infection to others.

Ellen Lindner / Verywell

Symptoms

Spotting the early signs and symptoms of flu can help you seek treatment that can shorten the course of an infection. The most common early symptoms are:

• Sudden high fever (over 100.4 degrees F)
• Chills
• Generalized muscle aches
• Malaise (a general feeling of unwellness)
• Tiredness
• Headache (usually extending across the forehead and behind the eyes)

Once full-fledged acute symptoms develop, there is really nothing you can do other than rest and let the disease run its course.

Causes

The flu is caused by a family of viruses that affect the respiratory system. Unlike colds, which can be caused by any number of different viruses (including rhinoviruses, adenoviruses, and coronaviruses), flu is caused exclusively by influenza viruses (designated as influenza type A, B, C, or D).

When flu symptoms first develop, it may be hard to differentiate them from the early signs of a cold. But, there are a few key ways to tell them apart.

Flu viruses almost invariably have a shorter incubation period, meaning that symptoms tend to develop fast and furiously, usually within a day or so. Because of this, the immune system will respond more aggressively, flooding the body with inflammatory compounds to help neutralize the virus.

This aggressive immune assault will manifest with symptoms that are usually more severe and/or less characteristic than the common cold.

Differences Between Colds and Flu
	Cold Symptoms	Flu Symptoms
Incubation period	2 to 3 days	1 to 2 days
Onset of symptoms	Gradually, between 4 to 7 days of exposure	Rapidly, between 1 to 3 days of exposure
Fever	Uncommon	Common, usually lasts 3 to 4 days
Chills	Uncommon	Common
Headache	Sometimes, usually related to sinus congestion	Common, related more to whole-body inflammation
Sneezing and congestion	Common	Occasionally
Cough	Common, mild to moderate	Common, often severe
Sore throat	Occasionally	Common
Fatigue	Occasionally, mild to moderate	Common, often severe

Stages of Infection

Influenza develops in stages, the early stage of which is referred to as the incubation phase and the latter of which is known as the acute phase.

The incubation phase is the time following exposure before symptoms first appear. It is during this phase that the virus will actively replicate and, by doing so, trigger the release of defensive proteins called cytokines. Cytokines are pro-inflammatory, meaning that they spur the body to generate inflammation so that tissues and blood vessels can swell to accommodate larger immune cells (known as monocytes).

In the latter part of the incubation phase, subtle symptoms will start to develop. These early symptoms are referred to as prodromal and serve as a warning sign of a developing infection.

After the prodromal phase is the acute phase, which lasts for around two to three days with all of the "classic" symptoms of flu. Most flu symptoms will disappear after about a week, but a cough may persist for up to two weeks.

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Diagnosis

The flu can usually be diagnosed by symptoms alone, particularly during flu season. This is especially true with the prodromal flu symptoms, during which treatment will often be dispensed presumptively. Even if a rapid influenza diagnostic test (RIDT) is available, the test is not all that sensitive and can regularly return false-negative results.

To prevent complications and the further spread of infection, certain prescription flu medications can be dispensed over the phone by a doctor or a telehealth physician without a face-to-face meeting.

Treatment

Unlike the common cold, for which there are no drug treatments, the flu can be shortened by a day or two if certain antiviral drugs are taken within 24 to 48 hours of the first appearance of symptoms. The drugs work by slowing the replication of the virus and, by doing so, potentially reduce the length and severity of the illness.

Even so, the drugs don't always work, often because people miss the early signs and get treated too late. If not taken within the first 24 to 48 hours, the drugs will likely be of any benefit.

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

• Rapivab (peramivir), approved for adults and children 2 years and up
• Relenza (zanamivir), approved for adults and children over 7 years
• Tamiflu (oseltamivir), approved for adults and children over 12 months
• Xofluza (baloxavir marboxil), approved for adults and children over 12 years

For people that are at high risk of flu complications (including young children, the elderly, pregnant women, and people with chronic health conditions), taking an antiviral drug can mean the difference between being hospitalized and recovering at home.

A Word From Verywell

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

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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. Truter I. Prodromal symptoms of flu: Malaise, rigors, fever and myalgia: Evidence-based pharmacy practice. SA Pharmaceut J. 2012 Jun;79(5):10.

2. Centers for Disease Control and Prevention. Flu symptoms and complications. Updated September 18, 2019.

3. Lessler J, Reich NG, Brookmeyer R, et al. Incubation periods of acute respiratory viral infections: A systematic review. Lancet Infect Dis. 2009 May;9(5):291-300. doi:10.1016/S1473-3099(09)70069-6

4. Centers for Disease Control and Prevention. Rapid influenza diagnostic tests. Updated October 25, 2016.

5. Shie, J., Fang, J. Development of effective anti-influenza drugs: congeners and conjugates – A review.J Biomed Sci. 2019;26:84. doi:10.1186/s12929-019-0567-0

6. GlaxoSmithKline. Relenza (zanamivir) inhalation powder, for oral inhalation. Updated December 2010.

7. Hoffmann-La Roche. Tamiflu complete product information sheet. Revised March 2011.

8. Genentech, Inc. Genentech: Xofluza TM (baloxavir Marboxil) - Information for healthcare providers. Updated October 2019.

9. Centers for Disease Control and Prevention. Who needs a flu vaccine and when?. Updated October 11, 2019.

What Are Some of the First Symptoms of the Flu

Source: https://www.verywellhealth.com/what-are-the-first-signs-of-the-flu-3894570

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