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The flu is an infection of the nose, throat, and lungs. It spreads easily.

This article discusses influenza types A and B. Another type of the flu is the swine flu (H1N1).

Video: Flu

Alternative Names

Influenza A; Influenza B; Oseltamivir (Tamiflu) - flu; Zanamivir (Relenza) - flu; Vaccine - flu


The flu is caused by an influenza virus.

Most people get the flu when they breathe in tiny airborne droplets from the coughs or sneezes of someone who has the flu. You can also catch the flu if you touch something with the virus on it, and then touch your mouth, nose, or eyes.

People often confuse colds and flu. They are different, but you might have some of the same symptoms. Most people get a cold several times a year. On the contrary, people generally get the flu only once every few years.

Video: The difference between a cold and the flu

Sometimes, you can get a virus that makes you throw up or have diarrhea. Some people call this the "stomach flu." This is a misleading name because this virus is not the actual flu. The flu mostly affects your nose, throat, and lungs.

Test Your Flu Prevention Knowledge

Which are common ways to catch the flu?

The correct answer is B and C. The best lifestyle change you can make to help prevent the flu is to wash your hands often.

Which of the following helps protect you from the flu?

The correct answer is all of the above. Washing your hands often helps stop the spread of germs. Eating a healthy diet and getting enough sleep help boost your immune system so you’re less likely to get sick.

Which of the following is NOT a symptom of the flu:

The correct answer is diarrhea. The flu causes symptoms in the nose, throat, and lungs. If you are experiencing flu symptoms, you should avoid contact with other people.

How long do flu symptoms last?

The correct answer is longer than 1 week. Fever and aches begin to go away between 2 and 4 days after getting the flu. Sneezing, dry cough, runny nose, and sore throat may continue for several days. You may feel tired for weeks. Get plenty of rest and drink a lot of fluids while you’re recovering from the flu.

Which of the following is NOT a treatment for the flu?

The correct answer is antibiotics. Antibiotics kill bacteria. They do not help fight viruses, and the flu is caused by a virus. Taking antibiotics when they are not needed increases your risk of getting an infection later that can't be treated with antibiotics. Don't ask your doctor for antibiotics when you have the flu.

How can you prevent spreading the flu when you’re sick?

The correct answer is all of the above. If you get the flu, do all you can to prevent the virus from spreading to friends, loved ones, and strangers.

You can get vaccinated for the flu with a nasal spray.

The correct answer is true. There are two types of flu vaccines: a flu shot and a nasal spray. The nasal spray is called FluMist. It uses a live, weakened virus instead of a dead one. If you are 2 to 49 years old, and are not pregnant, you may use this vaccine. Talk to your doctor about whether FluMist is right for you.

When is the best time to get the flu vaccine?

The correct answer is in October. The CDC recommends everyone 6 months and older receive the flu vaccine. You should get the vaccine at the start of flu season (around October in the U.S.). Getting the vaccine as late as March may still help.

Which of the following are side effects of the flu vaccine?

The correct answer is both A and B. Most people have no side effects from the flu shot. Others may notice soreness at the injection site, minor aches, and low-grade fever for a few days after the shot. Talk to your doctor if you have concerns about getting a flu shot.

Who should NOT receive a flu vaccine?

The correct answer is people who are sick and have a fever. If you have a fever or other illness, you should talk to your doctor before getting vaccinated. The CDC and most doctors recommend waiting until you are healthy to get the vaccine.

Washing your hands thoroughly is the best lifestyle change you can make to help prevent the flu.

The correct answer is true. Washing your hands often and carefully is the best lifestyle change you can make to help prevent the flu. You should wash your hands with soap and warm water for 15 to 20 seconds, about the time it takes to sing the Happy Birthday song twice.


Flu symptoms will often start quickly. You can start to feel sick about 1 to 7 days after you come in contact with the virus. Most of the time, symptoms appear within 2 to 3 days.

The flu spreads easily. It can affect a large group of people in a very short amount of time. For example, students and co-workers often get sick within 2 or 3 weeks of the flu's arrival in a school or workplace.

The first symptom is a fever between 102°F (39°C) and 106°F (41°C). An adult often has a lower fever than a child.

Other common symptoms include:

  • Body aches
  • Chills
  • Dizziness
  • Flushed face
  • Headache
  • Lack of energy
  • Nausea and vomiting

The fever, aches, and pains begin to go away on days 2 through 4. But new symptoms occur, including:

  • Dry cough
  • Increased symptoms that affect breathing
  • Runny nose (clear and watery)
  • Sneezing
  • Sore throat

Most symptoms go away in 4 to 7 days. The cough and tired feeling may last for weeks. Sometimes, the fever comes back.

Some people may not feel like eating.

The flu can make asthma, breathing problems, and other long-term (chronic) illnesses and conditions worse.

Exams and Tests

Most people do not need to see a health care provider when they have flu symptoms. This is because most people are not at risk for a severe case of the flu.

If you are very sick with the flu, you may want to see your provider. People who are at high risk for flu complications may also want to see a provider if they get the flu.

When many people in an area have flu, a provider can make a diagnosis after hearing about your symptoms. No further testing is needed.

There is a test to detect the flu. It is done by swabbing the nose or throat. Most of the time, test results are available very fast. The test can help your provider prescribe the best treatment.



Acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) help lower fever. Providers sometimes suggest that you use both types of medicine. DO NOT use aspirin.

Video: Tips on buying cold and flu medicines

A fever does not need to come all the way down to a normal temperature. Most people feel better when the temperature drops by 1 degree.

Over-the-counter cold medicines may make some of your symptoms better. Cough drops or throat sprays will help with your sore throat.

You will need a lot of rest. Drink plenty of liquids. DO NOT smoke or drink alcohol.


Most people with milder symptoms feel better in 3 to 4 days. They do not need to see a provider or take antiviral medicines.

Providers may give antiviral medicines to people who get very sick with the flu. You may need these medicines if you are more likely to have flu complications The health problems below may increase your risk of getting sicker with the flu:

  • Lung disease (including asthma)
  • Heart conditions (except high blood pressure)
  • Kidney, liver, nerve, and muscle conditions
  • Blood disorders (including sickle cell disease)
  • Diabetes
  • A weakened immune system due to diseases (such as AIDS), radiation therapy, or certain medicines, including chemotherapy and corticosteroids
  • Other long-term medical problems

These medicines may shorten the time you have symptoms by about 1 day. They work better if you start taking them within 2 days of your first symptoms.

Children at risk for a severe case of the flu may also need these medicines.

Outlook (Prognosis)

Millions of people in the United States get the flu each year. Most people get better within a week or two, but thousands of people with the flu develop pneumonia or a brain infection. They need to stay in the hospital. About 36,000 people in the United States die each year of problems from the flu.

Anyone at any age can have serious complications from the flu. Those at highest risk include:

  • People over the age of 65
  • Children younger than 2 years old
  • Women who are more than 3 months pregnant
  • Anyone living in a long-term care facility
  • Anyone with chronic heart, lung, or kidney conditions, diabetes, or a weakened immune system

Possible Complications

Complications may include:

When to Contact a Medical Professional

Call your provider if you get the flu and think you are at risk for having complications.

Also, call your provider if your flu symptoms are very bad and self-treatment is not working.


You can take steps to avoid catching or spreading the flu. The best step is to get a flu vaccine.

Nasal spray flu vaccine

Nasal spray flu vaccine

If you have the flu:

  • Stay in your apartment, dorm room, or home for at least 24 hours after your fever has gone.
  • Wear a mask if you leave your room.
  • Avoid sharing food, utensils, cups, or bottles.
  • Use hand sanitizer often during the day and always after touching your face.
  • Cover your mouth with a tissue when coughing and throw it away after use.
  • Cough into your sleeve if a tissue is not available. Avoid touching your eyes, nose, and mouth.

The Centers for Disease Control and Prevention (CDC) recommends that everyone 6 months and older should receive the influenza vaccine. Children 6 months through 8 years of age may need 2 doses during a single flu season. Everyone else needs only 1 dose each flu season. For the 2019-2020 season, the CDC recommends use of the flu shot (inactivated influenza vaccine or IIV) and the recombinant influenza vaccine (RIV). The nasal spray flu vaccine (live attenuated influenza vaccine, or LAIV) may be given to healthy, non-pregnant people 2 through 49 years of age.


Normal lung anatomy
Nasal spray flu vaccine


Aoki FY. Antiviral drugs for influenza and other respiratory virus infections. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 45.

Centers for Disease Control and Prevention website. Inactivated influenza VIS. www.cdc.gov/vaccines/hcp/vis/vis-statements/flu.html. Updated August 15, 2019. Accessed October 19, 2020.

Centers for Disease Control and Prevention website. Live, intranasal influenza VIS. www.cdc.gov/vaccines/hcp/vis/vis-statements/flulive.html. Updated August 15, 2019. Accessed October 19, 2020.

Centers for Disease Control and Prevention website. What you should know about flu antiviral drugs. www.cdc.gov/flu/antivirals/whatyoushould.htm. Updated January 25, 2021. Accessed February 17, 2021.

Havers FP, Campbell AJP. Influenza viruses. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 285.

Ison MG, Hayden FG. Influenza. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 340.

Treanor JJ. Influenza viruses, including avian influenza and swine influenza. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 165.

Review Date: 
Reviewed By: 
Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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