The flu, or influenza, is a viral disease of the respiratory tract—the nose, throat, bronchial tubes and lungs—and is highly contagious. It is spread though airborne droplets of moisture produced by coughs or sneezes. When you breathe these germs in through your nose or mouth, you may come down with the flu, generally within one to four days of exposure.

The flu is a potentially serious disease that can lead to hospitalization, or, in severe cases, death. Even healthy people can become very sick from the flu. Death rates from the flu vary from season to season. Flu-related deaths have ranged from a low of 3,000 to a high of 49,000 between 1976 and 2007, according to the U.S. Centers for Disease Control and Prevention (CDC). Outbreaks frequently start in school-age children, who carry the virus home and spread it to other groups.

And, beginning with the 2009-2010 flu season, there was a new flu to contend with—H1N1 flu (“swine flu”), which caused the first flu pandemic in more than 40 years. Since this outbreak, the seasonal flu vaccines have included coverage for the 2009 H1N1 flu. The seasonal trivalent flu vaccine usually contains one of each of the three kinds of influenza viruses that most commonly circulate among people today: influenza A (H1N1), influenza A (H3N2) and influenza B viruses. For the 2016-17 season, there are more flu vaccine options available than ever before. See the Prevention section for more information.

Flu seasons are unpredictable. There are some flu outbreaks every season, but it’s impossible to predict the timing, severity and length of the flu season from year to year. The flu season in the United States commonly peaks in January or February, but it can begin as early as October and continue into May.

Because flu can be so serious and can spread so rapidly, the CDC recommends that everyone age 6 months and older get vaccinated every year. Starting in 2016, the CDC recommends the flu shot, either trivalent or quadrivalent, for everyone. The nasal spray flu vaccine is no longer recommended for anyone. A yearly flu vaccine is the first and most important step in protecting against flu, according to the CDC.


Many people confuse the terms “cold” and “flu” because the illnesses share some of the same features. Both are caused by viruses that infect the respiratory tract, mainly during the winter, and both can cause symptoms such as coughing and sore throat. A cold is a minor viral infection of the nose and throat and can occur in any season. More than 200 viruses are known to cause the common cold.

It’s important to know the difference between the cold and flu because each illness is treated differently. You know you have the flu when you feel as though you’ve been hit by a truck and experience symptoms such as high fever, severe headache, muscle and body aches and extreme tiredness, along with coughing and nasal symptoms. A cold is less severe and often includes a runny nose, sneezing and coughing. Unlike flu, colds typically don’t cause fever.

Flu Symptoms

The flu causes muscle and joint pain, high fever, a deep cough, chills, fatigue and weakness that usually send you straight to bed for three to five days or longer. Afterward, cough and tiredness may persist for days or even weeks. Other symptoms include headache, eye pain and sometimes a stuffy nose and sore throat. Some strains of the flu also produce vomiting and diarrhea. Symptoms usually come on suddenly once you’ve been exposed to the virus.

While there is such a thing as “stomach flu,” it is not caused by the influenza virus. Most people with stomach flu are infected with one of the many gastroenteritis viruses that cause temporary nausea and vomiting.

If you’ve been in contact with someone who has the flu and you begin to experience flu-like symptoms, chances are you have the virus. Only your health care professional can diagnose your symptoms accurately, so it’s important to call for an appointment as soon as your symptoms develop to see if you’re a candidate for prescription antiviral medication.

If you think you’ve been exposed to someone who has the flu and you begin to experience symptoms, the CDC currently recommends you stay home and keep away from others as much as possible and avoid travel, work, school or public places for at least 24 hours after your fever is gone (without the use of fever-reducing medication) except to get medical care or for other necessities.

If you become severely ill or you are in one of the groups at high risk for complications, (children younger than five, pregnant women, people of any age with certain chronic medical conditions like asthma, COPD, diabetes or heart disease, people who are immunosuppressed due to HIV infection or because they are taking immunosuppressive medications, and people over age 65), call your health care professional or seek medical treatment.

In children, warning signs necessitating emergency medical care include fast breathing or trouble breathing; bluish or gray skin color; not drinking enough fluids; severe or persistent vomiting; not waking up or not interacting; being so irritable that the child does not want to be held; and flu-like symptoms that improve but then return with fever and worsening cough.

In adults, warning signs necessitating emergency medical care include difficulty breathing or shortness of breath; pain or pressure in the chest or abdomen; sudden dizziness; confusion; severe or persistent vomiting; and flu-like symptoms that improve but then return with fever and worsening cough.

Antiviral medications can be used to treat people who are severely ill with flu. To be effective, antiviral medications should be taken within 12 to 48 hours of the onset of symptoms.

Flu Complications

Flu often develops into acute bronchitis—an inflammation of the bronchi, the air passages or tubes to the lungs. Symptoms include:

  • A fever, 100 to 102 degrees Fahrenheit.
  • An irritating, dry, painful cough that starts to produce small amounts of white or light yellow sputum after two or three days; at this stage the fever often recedes, and the pain from coughing diminishes. If your sputum is yellow-green or green in color, you may have a bacterial infection.

Even after the condition improves, a slight cough commonly remains for another week or two. Most cases of acute bronchitis simply represent continued inflammation from viral infection, rather than a bacterial complication. Many people benefit from short-term use of an inhaled bronchodilator such as albuterol (Accuneb, Proventil, Ventolin or ProAir).

You usually don’t need antibiotics, regardless of how long your cough has lasted. However, if you have a cough for three weeks or more, you should be carefully evaluated to rule out pneumonia or bacterial bronchitis. If you are producing green secretions when you cough, you may have a bacterial infection and need antibiotics.

Pneumonia symptoms typically appear after you feel like you’ve just about recovered from the flu. Symptoms include:

  • high fever
  • shaking chills
  • chest pain with each breath
  • continuous hacking cough that produces thick, yellow-greenish-colored phlegm, or sputum, or sputum with blood in it
  • extreme weakness and fatigue

The Flu in Children

Children are both highly likely to get the flu and the most likely to transmit it to others. In fact, studies find that:

  • Children are more likely than adults to get the flu and to have complications with the illness. The flu is most serious in children under age 2.
  • Families with school-age children experience more flu infections than those without because schools are ideal locations for viruses to attack and spread. On average, about one-third of family members of school-aged children are infected with the flu each year.
  • Children do not have as much natural immunity to influenza as adults because they have had less lifetime exposure. Also, close contact with other children in school, home and day-care settings increases a child’s risk of getting and spreading the virus.


When you have the flu, the most important thing is rest. Plus, if you stay home, there’s less risk that you’ll spread the flu to other people. Flu can continue to be contagious for up to five to seven days after symptoms appear.

The following may help with flu symptoms:

  • Ask your health care professional about the prescription antiviral drugs oseltamivir (Tamiflu) or zanamivir (Relenza). Antivirals attack the virus at the source and should be started within 12 to 48 hours from the time the first symptoms appear to be effective. If taken within the proper timeframe, antivirals can help you feel better faster. Tamiflu, an oral medication available in capsule or liquid form, is approved for people one year and older. Relenza, an inhaled medication, is approved for people seven years and older. Side effects are mild and may include nausea and, less commonly, vomiting. Relenza may cause some nasal irritation.
  • Drink plenty of fluids. Hot liquids may relieve the feeling of congestion and loosen phlegm.
  • Take a pain reliever like acetaminophen for aches and fever. However, don’t use aspirin or products containing aspirin on anyone under 19 years of age, because there is a strong link between aspirin and Reye’s Syndrome, a disease that affects all body organs, particularly the brain and liver, in children.
  • Take a cough suppressant for relief from a dry, hacking cough when trying to sleep. A cough that produces mucus or phlegm is not necessarily a symptom of flu, but it can be a symptom of a cold or other illness. If you are coughing up phlegm, you may have developed a secondary bacterial infection that needs to be treated by a health care professional. Don’t use a suppressant if you are coughing up mucus; it’s important that you get those substances out of your lungs.
  • Use a humidifier, respirator or steamer in the bedroom to help ease congestion.

Because the flu is a viral infection, it cannot be treated with antibiotics. Antibiotics only kill bacteria and thus are useless against the flu. Taking antibiotics when you don’t need them contributes to an important public health problem—antibiotic resistance. Some diseases that were once easily cured by antibiotics have become resistant to treatment. For example, earlier this century, antibiotics nearly eliminated dreaded bacterial diseases like tuberculosis and gonorrhea. However, years of widespread misuse have allowed “antibiotic-resistant” forms of these illnesses to become more common.

However, if your health care professional finds that you’ve developed a bacterial infection such as pneumonia, you will likely need antibiotics. Take the full amount of medication as prescribed, even if you start feeling better. Otherwise, the infection may return. Never stockpile antibiotics or share them with other people.

Facts to Know

1. Influenza, or the flu, is a viral disease of the respiratory tract—the nose, throat, bronchial tubes and lungs. It’s similar to a cold in that both are caused by viruses that infect the respiratory tract, mainly in the winter season, and both can cause symptoms such as coughing and sore throat. A cold is a minor viral infection of the nose and throat, and its primary symptoms are nasal stuffiness, sneezing, runny nose, sore throat and cough. Influenza is more serious, and its major symptoms are high fever, severe aches and pains, cough with mucus production, tiredness and weakness.

2. The flu is highly contagious and is spread though airborne droplets of moisture produced when someone with the flu coughs or sneezes. When you breathe in these germs, you may come down with the flu, generally within one to four days of being exposed.

3. Rates of influenza infection vary among age groups and from one season to another, according to the U.S. Centers for Disease Control and Prevention (CDC).

4. Flu seasons are unpredictable, and in some years, flu outbreaks are severe. The CDC estimates that over a period of 31 years, the number of flu-related deaths has ranged from a low of about 3,000 to a high of about 49,000 Americans.

5. Smoking can increase your risk for the flu and complications from the flu, because smoking injures your airways and damages the cilia, tiny hair-like structures that help keep the airways clear.

6. The most serious, often life-threatening complication of the flu is pneumonia. Other complications include ear infection, bronchitis, dehydration and worsening of chronic conditions, such as congestive heart failure, asthma or diabetes. Croup and a lung disease called bronchiolitis can develop as complications in infants and young children.

7. The influenza virus changes its genetic makeup from year to year, which means that each year you’re likely exposed to a new virus. That’s why you can get the flu every year, and why a flu vaccine is recommended annually. Vaccines, which are made with killed or inactivated virus or viral fragments of those strains, work by forcing the immune system to make antibodies that fight circulating strains of influenza.

8. A flu vaccination is your best chance to protect yourself against the flu. You should get a seasonal flu vaccine every year because the flu vaccine is formulated to keep up with constantly changing flu viruses.

9. Prescription antiviral medications, such as oseltamivir (Tamiflu) and zanamivir (Relenza), can be used to treat and prevent the flu if used within 12 to 48 hours of symptom onset or exposure to the virus.