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 two 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 transferred from your hand when you touch your mouth or nose.

Risk Factors

Factors that increase your chance of getting the flu include:

  • Living or working in crowded conditions, such as nursing homes, schools, military forces, and daycare centers
  • Being physically or mentally disabled—people with disabilities may not be able to easily communicate their symptoms or may have trouble practicing preventive measures against the flu, putting them more at risk.

Certain groups of people are at a higher risk of developing complications from the flu. Risk factors for complications include:

  • Children younger than 5 years old
  • Adults aged 65 years and older
  • Being American Indian/Alaska Native
  • Certain health conditions, such as asthma, diabetes, or heart disease
  • A suppressed immune system
  • Pregnancy during the flu season
  • Age younger than 18 years old and receiving long-term aspirin therapy—may be at risk for Reyes syndrome
  • Living in nursing homes or other long-term care facilities
  • Obesity


If you have the flu, you might infect others one 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:

  • High fever and chills
  • Severe muscle aches
  • Severe fatigue
  • Headache
  • Decreased appetite or other gastrointestinal symptoms like nausea, vomiting, and diarrhea (more common in children than adults)
  • Runny nose, nasal congestion
  • Sneezing
  • Watery eyes or conjunctivitis
  • Sore throat
  • Cough
  • Swollen lymph nodes in the neck


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:

  • Pain relievers and fever reducers for adults, such as acetaminophen or ibuprofen
  • Cough remedies—to make a cough more productive or to suppress a cough
  • Decongestants—Do not use nasal spray longer than 3-5 days. You may experience an increase in congestion when you stop using the spray. This is called rebound effect.
  • Antihistimines

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:

  • Flu shot (injection)—all people aged 6 months and older should get the vaccine. Note: Children 8 years and younger may need 2 shots.
  • Nasal spray—the spray is approved for healthy, nonpregnant people aged 2-49 years old. Certain people, like those with weakened immune systems, should get the flu shot instead of the nasal spray. Talk to your doctor about which one is right for you. Note: The Centers for Disease Control and Prevention concluded that the nasal spray flu vaccine should not be used for the 2017-2018 flu season.

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:

  • Children less than 6 months old
  • Those who had a severe reaction to vaccination in the past
  • Those who have a history of Guillain-Barré syndrome
  • Those who are very sick and have a fever—talk to your doctor before being 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:

  • Wash your hands frequently, especially when you come in contact with someone who is sick. Wash your hands for 15-20 seconds with soap and water. Rubbing alcohol-based cleaners on your hands is also helpful.
  • Avoid close contact with people who have respiratory infections. The flu can spread starting one day before and ending 7 days after symptoms appear. If you have to be in close contact with a sick person, wear a face mask or a disposable respirator.
  • Cover your mouth and nose with a tissue when you cough or sneeze. Throw away the tissue after you use it. Coughing or sneezing into your elbow or upper sleeve is also helpful.
  • Do not share drinks or personal items.
  • Do not bite your nails or put your hands near your eyes, mouth, or nose.
  • Keep surfaces clean by wiping them with a household disinfectant.

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:

  • Are exposed to the flu
  • Are at high risk for complications
  • Are a healthcare worker, public health worker, or first responder

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:

  • Avoid close contact with people. Before you can return to school or work, your fever should be gone for at least 24 hours without the help of fever-reducing medication. This could take up to 7 days after symptoms first appear. It is important to stay home if you have the flu, leaving your house only to see your doctor.
  • If you cannot avoid close contact, cover your mouth and nose with a face mask.
  • Wash your hands for 15-20 seconds with soap and water. Even if someone in your house has the flu, you may be able to avoid getting sick by washing your hands. Using a hand sanitizer is also helpful.
  • Cover your mouth and nose with a tissue when you cough or sneeze. Throw away the tissue after you use it. Coughing or sneezing into your elbow or upper sleeve will also keep you from spreading the flu with your hands. Do not spit.
  • Do not share drinks or personal items.
  • Wash eating utensils with hot water and soap.
  • Do not bite your nails or put your hands near your eyes, mouth, or nose.
  • Keep surfaces clean by wiping them with a household disinfectant.
  • Use the hot setting on your washing machine when washing infected laundry.