The flu (also called influenza) is a viral infection that affects the respiratory system. It can cause mild-to-severe illness, and sometimes it can lead to death.
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The influenza virus causes the flu. In temperate climates each winter, the virus spreads around the world. The strains are usually different from one year to the next. While less likely, it is possible to get the flu when it is not flu season (especially in tropical climates).
The 2 main kinds of influenza virus are Type A and Type B. There is also a Type C, but it is less common and not as virulent.
Someone infected with the virus may sneeze or cough. This releases droplets into the air. If you breathe in infected droplets, you can become infected. You can also become infected by touching a contaminated surface. The virus is then transferred from your hand when you touch your mouth or nose.
Factors that increase your chance of getting the flu include:
Certain groups of people are at a higher risk of developing complications from the flu. Risk factors for complications include:
If you have the flu, you might infect others 1 day before symptoms start and up to 5 days (sometimes more) after you become sick. This means you may be infecting others even before you know you are sick.
Symptoms usually start abruptly. They may include:
You will be asked about your symptoms and medical history. Diagnosis of the flu is usually based on symptoms.
In some cases, your doctor may take samples from your nose or throat to confirm the diagnosis.
During recovery, it is important to rest as much as possible and drink plenty of fluids, including water, juice, or caffeine-free tea. The flu generally lasts 7-10 days. A cough or fatigue may last longer.
Other treatment may include:
Most people with the flu do not need antiviral medication. Check with your doctor. You may need the medication if you are in a high-risk group or if you have a severe illness.
Antiviral medications generally may help relieve symptoms and shorten the time you are sick. They must be taken within 48 hours of the first symptoms. Some strains of the seasonal influenza virus are resistant to these medications.
Over-the-counter (OTC) or prescription medications can be used to ease flu symptoms:
Note: OTC cough and cold products should not be used to treat infants or children less than 2 years old. Rare, but serious side effects have been reported. They include death, convulsions, rapid heart rates, and decreased levels of consciousness. Serious side effects have also been reported in children aged 2-11 years. Research is still going on for the safety of OTC products for this age group.
Note: Aspirin is not recommended for children with a current or recent viral infection. Check with your doctor before giving your child aspirin.
The best way to prevent getting the flu is to be vaccinated. You will need to be vaccinated each year since the virus may change every season. Two forms of the vaccine are available:
For the best protection, get vaccinated as soon as the vaccine is available in your area. Vaccinations are offered throughout the flu season, which may begin as early as October.
It takes about 2 weeks for the vaccine to protect you against the flu.
There are people who should not be vaccinated:
Some different types of flu vaccines are okay for people with egg allergies. Talk to your doctor about which flu vaccine is right for you.
There are general measures you can take to reduce your risk of getting the flu:
Sometimes it is beneficial to take antiviral medications to prevent the flu. You may want to talk to your doctor about taking these medications to lower your risk of getting the flu if you:
If you have the flu and live with someone who is at risk for complications (such as elderly, babies, someone with cancer), that person may need to take antiviral medications to prevent getting the flu from you.
Remember that these medications are not a substitute for being vaccinated. Vaccination is still the best way to prevent the flu.
If you have the flu, take these steps to avoid spreading it to others:
Centers for Disease Control and Prevention
World Health Organization
Public Health Agency of Canada
The College of Family Physicians of Canada
Antiviral medications for influenza prophylaxis. EBSCO DynaMed website. Available at: http://www.dynamed.com/topics/dmp~AN~T474389/Antiviral-medications-for-influenza-prophylaxis. Updated October 27, 2016.. Accessed September 26, 2017.
Antiviral medications for the treatment of influenza.. EBSCO DynaMed website. Available at: http://www.dynamed.com/topics/dmp~AN~T911104/Antiviral-medications-for-the-treatment-of-influenza. Updated June 28, 2017. Accessed September 26, 2017.
Immunization schedules. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/vaccines/schedules/index.html. Updated February 6, 2017. Accessed September 26, 2017.
Inactivated influenza VIS. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/vaccines/hcp/vis/vis-statements/flu.html. Updated October 18, 2016. Accessed September 26, 2017.
Influenza. American Lung Association website. Available at:
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Accessed September 26, 2017.
Influenza. National Institute of Allergy and Infectious Disease website. Available at: https://www.niaid.nih.gov/diseases-conditions/influenza. Updated July 21, 2015. Accessed September 26, 2017.
Influenza in adults. EBSCO DynaMed website. Available at: http://www.dynamed.com/topics/dmp~AN~T435301/Influenza-in-adults. Updated September 11, 2017. Accessed September 26, 2017.
Influenza in children. EBSCO DynaMed website. Available at: http://www.dynamed.com/topics/dmp~AN~T435305/Influenza-in-children. Updated September 27, 2016. Accessed September 26, 2017.
Key facts about seasonal influenza (flu). Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/flu/keyfacts.htm. Updated August 25, 2016. Accessed September 26, 2017.
Live, intranasal influenza VIS. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/vaccines/hcp/vis/vis-statements/flulive.html. Updated October 18, 2016. Accessed September 26, 2017.
Preventing seasonal flu. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/flu/prevent/index.html. Updated July 28, 2017. Accessed September 26, 2017.
What you should know about flu antiviral drugs. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/flu/antivirals/whatyoushould.htm. Updated January 5, 2017. Accessed September 26, 2017.
3/1/2007 DynaMed Systematic Literature Surveillance http://www.dynamed.com/topics/dmp~AN~T268332/Seasonal-influenza-vaccines-in-children: Belshe RB, Edwards KM, et al. Live attenuated versus inactivated influenza vaccine in infants and young children. N Engl J Med. 2007;356(7):685-696.
11/9/2009 DynaMed Systematic Literature Surveillance http://www.dynamed.com/topics/dmp~AN~T435301/Influenza-in-adults: Cowling BJ, Chan KH, et al. Facemasks and hand hygiene to prevent influenza transmission in households: a cluster randomized trial. Ann Intern Med. 2009;151(7):437-446.
4/16/2010 DynaMed Systematic Literature Surveillance http://www.dynamed.com/topics/dmp~AN~T435301/Influenza-in-adults: Aiello AE, Murray GF, et al. Mask use, hand hygiene, and seasonal influenza-like illness among young adults: a randomized intervention trial. J Infect Dis. 2010;201(4):491-498.
Last reviewed September 2018 by
EBSCO Medical Review Board
Marcie L. Sidman, MD
Last Updated: 7/28/2020