If you get sick with flu, antiviral drugs may be a treatment option.

Check with your doctor promptly if you are at higher risk of serious flu complications and you get flu symptoms.  People at higher risk of flu complications include young children, adults 65 years of age and older, pregnant people, and people with certain medical conditions, such as asthma, diabetes and heart disease.

When used for treatment, antiviral drugs can lessen symptoms and shorten the time you are sick by 1 or 2 days. They also can prevent serious flu complications, like pneumonia. For people at higher risk of serious flu complications, treatment with antiviral drugs can mean the difference between milder or more serious illness possibly resulting in a hospital stay. CDC recommends prompt treatment for people who have flu or suspected flu and who are at higher risk of serious flu complications.

How to prevent Flu?

Take time to get a flu vaccine.

• CDC recommends a yearly flu vaccine as the first and most important step in protecting against flu viruses.
• Flu vaccines help to reduce the burden of flu illnesses, hospitalizations and deaths on the health care system each year. (Read more about flu vaccine benefits.
• This season, all flu vaccines will be designed to protect against the four flu viruses that research indicates will be most common. (Visit Vaccine Virus Selection for this season’s vaccine composition.)
• Everyone 6 months and older should get an annual flu vaccine, ideally by the end of October. Learn more about vaccine timing.
• Vaccination of people at higher risk of developing serious flu complications is especially important to decrease their risk of severe flu illness.
• People at higher risk of serious flu complications include young children, pregnant people, people with certain chronic health conditions like asthma, diabetes or heart and lung disease, and people 65 years and older.
• Vaccination also is important for health care workers, and other people who live with or care for people at higher risk to keep from spreading flu to them. This is especially true for people who work in long-term care facilities, which are home to many of the people most vulnerable to flu.
• Children younger than 6 months are at higher risk of serious flu illness but are too young to be vaccinated. People who care for infants should be vaccinated instead.

Take everyday preventive actions to stop the spread of germs.

• Take everyday preventive actions that are recommended to reduce the spread of flu.
  • Avoid close contact with people who are sick.
  • If you are sick, limit contact with others as much as possible to keep from infecting them.
• Cover coughs and sneezes.
  • Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it.
• Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub.
• Avoid touching your eyes, nose, and mouth. Germs spread this way.
• Clean and disinfect surfaces and objects that may be contaminated with viruses that cause flu.
• For flu, CDC recommends that people stay home for at least 24 hours after their fever is gone except to get medical care or other necessities. Fever should be gone without the need to use a fever-reducing medicine. Note that the stay-at-home guidance for COVID-19 may be different. Learn about some of the similarities and differences between flu and COVID-19.

Take flu antiviral drugs if your doctor prescribes them.

• If you are sick with flu, antiviral drugs can be used to treat your illness.
• Antiviral drugs are different from antibiotics. They are prescription medicines (pills, liquid or an inhaled powder) and are not available over-the-counter.
• Flu antiviral drugs can make flu illness milder and shorten the time you are sick. They may also prevent serious flu complications. For people with higher risk factors
  [308 KB, 2 Pages], treatment with an antiviral drug can mean the difference between having a milder illness versus a very serious illness that could result in a hospital stay.
• Studies show that flu antiviral drugs work best for treatment when they are started within 2 days of getting sick, but starting them later can still be helpful, especially if the sick person has a higher risk factor or is very sick from flu.
• If you are at higher risk from flu and get flu symptoms, call your health care provider early so you can be treated with flu antivirals if needed. Follow your doctor’s instructions for taking this drug.

Flu symptoms include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and fatigue. Some people also may have vomiting and diarrhea. People may be infected with flu and have respiratory symptoms without a fever. Visit CDC’s website to find out what to do if you get sick with flu. Learn about some of the similarities and differences between flu and COVID-19, and the difference between flu and the common cold.

The best way to reduce the risk of flu and its potentially serious complications is by getting vaccinated each year.

Flu Symptoms

Influenza (flu) can cause mild to severe illness, and at times can lead to death. Flu symptoms usually come on suddenly. People who have flu often feel some or all of these symptoms:

• fever* or feeling feverish/chills
• cough
• sore throat
• runny or stuffy nose
• muscle or body aches
• headaches
• fatigue (tiredness)
• some people may have vomiting and diarrhea, though this is more common in children than adults.

*It’s important to note that not everyone with flu will have a fever.

More information is available at  Flu and COVID-19 symptoms.

On This Page

• What is Influenza (also called Flu)?
• How Flu Spreads
• How Many People Get Sick with Flu Every Year?
• Period of Contagiousness
• Onset of Symptoms
• Complications of Flu
• People at High Risk from Flu
• Preventing Seasonal Flu
• Diagnosing Flu
• Treating Flu

How Flu Spreads

Most experts believe that flu viruses spread mainly by tiny droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose or possibly their eyes.

How Many People Get Sick with Flu Every Year?

A 2018 CDC study published in Clinical Infectious Diseases

looked at the percentage of the U.S. population who were sickened by flu using two different methods and compared the findings. Both methods had similar findings, which suggested that on average, about 8% of the U.S. population gets sick from flu each season, with a range of between 3% and 11%, depending on the season.

Why is the 3% to 11% estimate different from the previously cited 5% to 20% range?

The commonly cited 5% to 20% estimate was based on a study that examined both symptomatic and asymptomatic influenza illness, which means it also looked at people who may have had the flu but never knew it because they didn’t have any symptoms. The 3% to 11% range is an estimate of the proportion of people who have symptomatic flu illness.

Who is most likely to be infected with influenza?

The same CID study

found that children are most likely to get sick from flu and that people 65 and older are least likely to get sick from influenza. Median incidence values (or attack rate) by age group were 9.3% for children 0-17 years, 8.8% for adults 18-64 years, and 3.9% for adults 65 years and older. This means that children younger than 18 are more than twice as likely to develop a symptomatic flu infection than adults 65 and older.

How is seasonal incidence of influenza estimated?

Influenza virus infection is so common that the number of people infected each season can only be estimated. These statistical estimations are based on CDC-measured flu hospitalization rates that are adjusted to produce an estimate of the total number of influenza infections in the United States for a given flu season.

The estimates for the number of infections are then divided by the census population to estimate the seasonal incidence (or attack rate) of influenza.

Does seasonal incidence of influenza change based on the severity of flu season?

Yes. The proportion of people who get sick from flu varies. A paper published in CID

found that between 3% and 11% of the U.S. population gets infected and develops flu symptoms each year. The 3% estimate is from the 2011-2012 season, which was an H1N1-predominant season classified as being of low severity. The estimated incidence of flu illness during two seasons was around 11%; 2012-2013 was an H3N2-predominant season classified as being of moderate severity, while 2014-2015 was an H3N2 predominant season classified as being of high severity.

Table 1. Estimates of the Incidence of Symptomatic Influenza by Season and Age-Group, United States, 2010–2016

Season	Predominant Virus(es)	Season Severity	Incidence, %, by Age Group
			0-4 yrs		5-17 yrs		18-49 yrs		50-64 yrs		≥65 yrs		All Ages
2010-11	A/H3N2, A/H1N1pdm09	Moderate	14.1		8.4		5.3		8.1		4.3		6.8
2011-12	A/H3N2	Low	4.8		3.6		2.5		3.1		2.3		3.0
2012-13	A/H3N2	Moderate	18.6		12.7		8.9		14.3		9.9		11.3
2013-14	A/H1N1pdm09	Moderate	12.4		7.2		9.2		13.0		3.4		9.0
2014-15	A/H3N2	High	15.0		12.7		7.8		12.9		12.4		10.8
2015-16	A/H1N1pdm09	Moderate	11.1		7.4		7.1		11.0		3.5		7.6
Median			13.2		7.9		7.4		12.0		3.9		8.3

Period of Contagiousness

You may be able to spread flu to someone else before you know you are sick, as well as while you are sick.

• People with flu are most contagious in the first 3-4 days after their illness begins.
• Some otherwise healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick.
• Some people, especially young children and people with weakened immune systems, might be able to infect others for an even longer time.

Onset of Symptoms

The time from when a person is exposed and infected with flu to when symptoms begin is about 2 days, but can range from about 1 to 4 days.

Complications of Flu

Complications of flu can include bacterial pneumonia, ear infections, sinus infections and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes.

People at High Risk from Flu

Anyone can get flu (even healthy people), and serious problems related to flu can happen at any age, but some people are at high risk of developing serious flu-related complications if they get sick. This includes people 65 years and older, people of any age with certain chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women, and children younger than 5 years.

Preventing Seasonal Flu

The first and most important step in preventing flu is to get a flu vaccine each year. Flu vaccine has been shown to reduce flu related illnesses and the risk of serious flu complications that can result in hospitalization or even death. CDC also recommends everyday preventive actions (like staying away from people who are sick, covering coughs and sneezes and frequent handwashing) to help slow the spread of germs that cause respiratory (nose, throat, and lungs) illnesses, like flu.

Diagnosing Flu

It is very difficult to distinguish flu from other viral or bacterial respiratory illnesses based on symptoms alone. There are tests available to diagnose flu. More information is available: Diagnosing Flu.

Treating Flu

There are influenza antiviral drugs that can be used to treat flu illness.