Stages of the Flu

Between fatigue, cough, and fever, flu symptoms can affect your whole body, and they often come on suddenly. Fortunately, the worst part of the flu is usually over in a few days.

Here are the common stages of the flu, and how you can take care of yourself at each stage.

Incubation Phase

In the early stages of the flu, you don’t even know you have it. The virus replicates in your body for one to four days after you get infected.

During this time, your immune system hasn’t yet launched a full-blown assault, which is what causes flu symptoms. But because the virus is active and replicating, people are often contagious a day before they develop symptoms.

If you spent time with other people the day before you got sick, you could have spread the virus without knowing it.

You may want to notify your close contacts, such as those you shared a meal or conversation with. That way, they can avoid seeing others who are elderly or at high risk of getting very sick from the flu.

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Days One to Three of Symptoms

Unlike a cold, the flu comes on quickly. On the first day, you may experience a fever, chills, headache, body aches, and cough. Typically, symptoms are the worst in the early stages of flu, which is the first two or three days.

You also may experience a sore throat, sneezing, and a stuffy nose. But these symptoms tend to be less common with a flu and more common with a cold.

If you’re at high-risk of getting very sick from the flu, call your doctor. They can prescribe an antiviral drug that can reduce the chances of pneumonia and other complications. But the drug has a much higher chance of working if you take it within 48 hours of developing symptoms.

How to take care of yourself during the early stages of the flu

In most cases, you can treat the flu at home. If your fever makes you uncomfortable or unable to sleep, you can bring down your fever with acetaminophen or ibuprofen.

However, if your fever rises above 103°F, or doesn’t come down with treatment, call your doctor.

A fever can make you dehydrated, so be sure to drink plenty of fluids. Water is great, but add in other liquids — such as juice, broth, and sports drinks. That way, you’ll get the sodium and sugars your body needs.

Try to avoid caffeine, which can make you dehydrated and disrupt your sleep (which is really important when you’re sick).

“Hydration is very important when you have been diagnosed with the flu,” says Cody Allan Smith, DO, of UPMC Family Medicine South.  “If you do not like the taste of water or all the sugar in sports drinks, you can mix one part water and one part sports drink for some flavor with less sugar.”

The same over-the-counter (OTC) medications that treat fever – acetaminophen and ibuprofen – also relieve headaches, body aches, and a sore throat. If congestion is bothering you, you can try a decongestant or nasal spray to break up the mucus.

You may not feel very hungry, as your body directs energy to fighting the virus rather than digesting food. You might prefer to eat small amounts of easy-to-digest foods, like soup, Jell-O, or apple sauce, rather than a large meal. If you live alone, ask a friend to drop off such food items, as well as any OTC medications you might need.

Days Four to Seven of Symptoms

Many people find their symptoms get better around day four. Those who don’t experience any complications from the flu should recover in about a week.

If you received a flu vaccination, your recovery time will likely be faster and your symptoms milder. While flu vaccination doesn’t always prevent infection, it primes the immune system to recognize and fight the flu more quickly.

During this time, you likely won’t feel feverish, but you may still feel quite tired and weak. This is normal – fighting the flu can deplete your energy.

How to take care of yourself during the later stages of the flu

Your appetite is likely increasing but may not be fully back yet. Take this time to eat nourishing food – fruits, vegetables, protein-rich food, and whole grains.

It’s important not to go back right away to your typical activity level. You’ll still likely need more rest than usual.

So, skip the gym for now and start with a light walk. You can increase your activity over the next days and weeks, as your energy levels increase.

Day 8 and Beyond

Some people have a lingering cough for a few weeks after the flu. Cough is especially common in elderly people and those with lung conditions.

If a lingering cough is keeping you up at night, or if you have difficulty breathing when coughing, call your doctor. You should also call your doctor if your cough improves but then takes a turn for the worst.

When to Seek Medical Attention for a Flu

A flu can worsen underlying diseases, like heart disease, asthma, or diabetes. Some people with the flu also need hospital care because of dehydration. In addition, the flu can infect the lungs, leading to pneumonia.

In extreme cases, the flu can cause organ damage or dangerous swelling in the heart or brain.

If you experience any of the following signs of flu complications, seek medical care right away:

  • Difficulty breathing.
  • Chest pain (including chest pain with coughing or breathing).
  • Seizures.
  • Extreme weakness (an inability to get out of bed, for instance).
  • Signs of dehydration (like a dry mouth and little to no urination).
  • Dizziness or confusion.
  • Signs an underlying health condition is getting worse.

Preventing Flu in the Future

The best way to prevent getting the flu again is to get your flu vaccine. The flu shot is safe and effective in keeping you from catching the flu and spreading it.

The Centers for Disease Control and Prevention (CDC) recommends that everyone older than 6 months should get a flu shot, with rare exceptions. Exceptions include people who have severe, life-threatening allergies and those with a history of Guillain-Barré Syndrome.

Ask your doctor if it’s too late for you to get your flu shot this season; if it is, mark your calendar to get your flu shot next September or October before the next flu season.

Where to get a flu shot

Flu shots are offered at many locations, including your doctor’s office, pharmacies, grocery stores with pharmacies. Many places offer flu shots free of charge. The Pennsylvania Department of Health offers flu vaccines to those who are uninsured and underinsured. For information, call 1-877-PA-HEALTH (1-877-724-3258).

At UPMC, there are many places to get your flu shot.  Find the location closest to you.


Editor's Note: This article was originally published on , and was last reviewed on .

American Lung Association. Flu symptoms, causes, and risk factors. Link

Drs. Sameh Boktor and John Hafner. Influenza. StatPearls. Link

Centers for Disease Control and Prevention. Flu symptoms and complications. Link

Centers for Disease Control and Prevention. Key facts about influenza. Link

Centers for Disease Control and Prevention. Study shows hospitalization rates and risk of death from seasonal flu increase with age among people 65 years and older. Link

Centers for Disease Control and Prevention. Influenza Antiviral Medications: Summary for Clinicians. Link

National Library of Medicine. Fever. Link

National Library of Medicine. Flu. Link

Rachel Rabkin Peachman. A Day-by-Day Guide to Treating a Cold or the Flu. Consumer Reports. Link

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